NIMP| Valentin TEODORESCU, Author at NIMP

Publications

1. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al₂O₃/Ge/Al₂O₃ Memory Structures

Authors: Stavarache, I; Palade, C; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: 2024 JAN 17 2024, ACS APPLIED ELECTRONIC MATERIALS, DOI: 10.1021/acsaelm.3c01454

For the development of memory devices for the continuous advancement of IT engineering, a good understanding of the charging-discharging mechanisms in nanocrystalline floating gate memories is crucial to overcoming the current limitations. The charging-discharging mechanism in Al2O3/Ge/Al2O3 trilayer memory structures obtained by magnetron sputtering deposition is investigated as a function of the postdeposition annealing temperature, up to 900 degrees C. The change by annealing of C-V hysteresis curves from a clockwise type at low temperatures to counterclockwise one in a sample annealed within the intermediary temperature range of 550 to 650 degrees C, and then, a return to a clockwise type for annealing within the higher temperature range of 800-900 degrees C was observed. Up to 700 degrees C, memory performances are constantly improved reaching for 600 degrees C annealed samples, a memory window of 5.6 V for voltage sweep in the range -1 to +15 V, and good retention characteristics for 650 degrees C annealed structures, in which the charge loss is only similar to 2% after 10(8) s. When the annealing temperature was increased above 700 degrees C, a rapid decrease in the memory performance takes place. The annealing-induced changes are explained based on the Ge fast diffusion and nanocrystallization process, in correlation with morphological and structural high-resolution transmission electron microscopy results.

2. Enhancing SiGeSn nanocrystals SWIR photosensing by high passivation in nanocrystalline HfO₂ matrix

Authors: Dascalescu, I; Palade, C; Slav, A; Stavarache, I; Cojocaru, O; Teodorescu, VS; Maraloiu, VA; Lepadatu, AM; Ciurea, ML; Stoica, T

Published: FEB 12 2024, SCIENTIFIC REPORTS, 14, 3532, DOI: 10.1038/s41598-024-53845-z

SiGeSn nanocrystals (NCs) in oxides are of considerable interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in NCs. We present a detailed study regarding the silicon germanium tin (SiGeSn) NCs embedded in a nanocrystalline hafnium oxide (HfO2) matrix fabricated by using magnetron co-sputtering deposition at room temperature and rapid thermal annealing (RTA). The NCs were formed at temperatures in the range of 500-800 degrees C. RTA was performed to obtain SiGeSn NCs with surfaces passivated by the embedding HfO2 matrix. The formation of NCs and beta-Sn segregation were discussed in relation to the deposition and processing conditions by employing HRTEM, XRD and Raman spectroscopy studies. The spectral photosensitivity exhibited up to 2000 nm in short-wavelength infrared (SWIR) depending on the Sn composition was obtained. Comparing to similar results on GeSn NCs in SiO2 matrix, the addition of Si offers a better thermal stability of SiGeSn NCs, while the use of HfO2 matrix results in better passivation of NCs increasing the SWIR photosensitivity at room temperature. These results suggest that SiGeSn NCs embedded in an HfO2 matrix are a promising material for SWIR optoelectronic devices.

3. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al₂O₃/Ge/Al₂O₃ Memory Structures

Authors: Stavarache, I; Palade, C; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: JAN 17 2024, ACS APPLIED ELECTRONIC MATERIALS, 6, DOI: 10.1021/acsaelm.3c01454

4. Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization

Authors: Lepadatu, AM; Stavarache, I; Palade, C; Slav, A; Dascalescu, I; Cojocaru, O; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: 2024 MAR 4 2024, JOURNAL OF PHYSICAL CHEMISTRY C, DOI: 10.1021/acs.jpcc.3c06996

The development of new materials for short-wavelength infrared (SWIR) optical sensors is of high importance for the fast development of different applications, as, for example, Internet of Things, road safety, and pollution monitoring. Group IV SiGe provides more sustainable As-, Cd-, and Pb-free nanomaterials that are cheaper and ecologic and offer easy integration with CMOS technology. This Review is on Ge and SiGe quantum dots/nanocrystals (QDs/NCs) embedded in dielectrics for VIS-SWIR photodetection, in which we highlight and discuss photocurrent mechanisms, correlation of photodetection parameters and characteristics with crystalline structure, morphology and energy bandgap, and applications as photodetectors, optical sensors, phototransistors, and solar cells. The embedding matrix induces NC surface passivation, stress field, and nanocrystallization effects and brings specific advantages depending on the matrix material. SiGe NCs in oxides for VIS-SWIR sensing represents a niche domain, showing high photosensitivity (photocurrent) in SWIR up to 1.8 mu m at room temperature and 2 mu m at 100 K, deeper in SWIR than Ge. By alloying Ge with a small content of Si, NC thermal stability is much improved as the detrimental Ge fast diffusion in oxides is hindered and SWIR photosensing is enhanced due to light absorption in Ge-rich SiGe NCs.

5. Up-conversion emission in transition metal and lanthanide co-doped systems: dimer sensitization revisited

Authors: Avram, D; Colbea, C; Patrascu, AA; Istrate, MC; Teodorescu, V; Tiseanu, C

Published: FEB 7 2023, SCIENTIFIC REPORTS, 13, 2165, DOI: 10.1038/s41598-023-28583-3

Lanthanide (Ln) co-doped transition metal (TM) upconversion (UC) co-doped systems are being intensively investigated for their exciting applications in photonics, bioimaging, and luminescence thermometry. The presence of TM, such as Mo6 + /W6 +, Mn2 +, or Fe3 + determines significant changes in Ln UC emission, such as intensity enhancement, colour modulation, and even the alteration of the photon order. The current mechanism assumes a ground-state absorption/excited-state absorption (ESA/GSA) in TM-Yb dimer followed by direct energy transfer to Er/Tm excited states. We revisit this mechanism by addressing two issues that remain ignored: a dynamical approach to the investigation of the upconversion mechanism and the intrinsic chemical complexity of co-doped TM, Ln systems. To this aim, we employ a pulsed, excitation variable laser across a complete set of UC measurements, such as the emission and excitation spectra and emission decays and analyze multiple grains with transmission electron microscopy (TEM). In the Mo co-doped garnet, the results sustain the co-existence of Mo-free garnet and Mo oxide impurity. In this Mo oxide, the Er upconversion emission properties are fully explained by a relatively efficient sequential Yb to Er upconversion process, with no contribution from Yb-Mo dimer sensitization.

6. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAY 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202207390

A new approach for the stabilization of the ferroelectric orthorhombic ZrO2 films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiOx/W(14 nm)/ZrO2(8 nm)/W(22 nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8 mu C cm(-2), remnant polarization of 12.7 mu C cm(-2) and coercive field of 1.2 MV cm(-1). The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0 x 10(5) cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.

7. Titania nanoparticles for photocatalytic degradation of ethanol under simulated solar light

Authors: Goncearenco, E; Morjan, IP; Fleaca, CT; Dumitrache, F; Dutu, E; Scarisoreanu, M; Teodorescu, VS; Sandulescu, A; Anastasescu, C; Balint, I

Published: MAY 22 2023, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 14, DOI: 10.3762/bjnano.14.51

TiO2 nanoparticles were synthesized by laser pyrolysis from TiCl4 vapor in air in the presence of ethylene as sensitizer at different working pressures (250-850 mbar) with and without further calcination at 450 degrees C. The obtained powders were analyzed by energydispersive X-ray spectroscopy, X- ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy. Also, specific surface area and photoluminescence with optical absorbance were evaluated. By varying the synthesis parameters (especially the working pressure), different TiO2 nanopowders were obtained, whose photodegradation properties were tested compared to a commercial Degussa P25 sample. Two series of samples were obtained. Series "a" includes thermally treated TiO2 nanoparticles (to remove impurities) that have different proportions of the anatase phase (41.12-90.74%) mixed with rutile and small crystallite sizes of 11-22 nm. Series "b" series represents nanoparticles with high purity, which did not require thermal treatment after synthesis (ca. 1 atom % of impurities). These nanoparticles show an increased anatase phase content (77.33-87.42%) and crystallite sizes of 23-45 nm. The TEM images showed that in both series small crystallites form spheroidal nanoparticles with dimensions of 40-80 nm, whose number increases with increasing the working pressure. The photocatalytic properties have been investigated regarding the photodegradation of ethanol vapors in Ar with 0.3% O2 using P25 powder as reference under simulated solar light. During the irradiation H-2 gas production has been detected for the samples from series "b", whereas the CO2 evolution was observed for all samples from series "a".

8. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAR 2023, ADVANCED SCIENCE, DOI: 10.1002/advs.202207390

9. Ferroelectric Orthorhombic ZrO₂ Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAY 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202207390

10. Lead-Free Perovskite Thin Films with Tailored Pockels-Kerr Effects for Photonics

Authors: Ion, V; Teodorescu, V; Birjega, R; Dinescu, M; Mitterbauer, C; Alexandrou, I; Ghitiu, I; Craciun, F; Scarisoreanu, ND

Published: JUL 27 2023, ACS APPLIED MATERIALS & INTERFACES, 15, DOI: 10.1021/acsami.3c06499

Pockels and Kerr effects are linear and nonlinear electro-opticaleffects, respectively, used in many applications. The modulation ofthe refractive index is employed in different photonic circuits. However,the greatest challenge is in photonic elements for quantum computingat room temperature. For this aim, materials with strong Pockels/Kerreffects and & chi;((2))/& chi;((3)) nonlinearsusceptibilities are necessary. Here, we demonstrate composition-modulatedstrong electro-optical response in epitaxial films of (Ba,Ca)(Ti,Zr)O-3 perovskite titanate. These films are grown by pulsed laserdeposition on SrTiO3. Depending on the ratios of Ca/Baand Ti/Zr, films show high Pockels or Kerr optical nonlinearities.We relate the variable electro-optic response to the occurrence ofnanopolar domains with different symmetries in a selected compositionrange. These findings open the route to easily implement nonlinearoptical elements in integrated photonic circuits.

11. Multifunctional Zn-Doped ITO Sol-Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material

Authors: Gartner, M; Anastasescu, M; Calderon-Moreno, JM; Nicolescu, M; Stroescu, H; Hornoiu, C; Preda, S; Predoana, L; Mitrea, D; Covei, M; Maraloiu, VA; Teodorescu, VS; Moldovan, C; Petrik, P; Zaharescu, M

Published: SEP 2022, NANOMATERIALS, 12, 3244, DOI: 10.3390/nano12183244

Undoped and Zn-doped ITO (ITO:Zn) multifunctional thin films were successfully synthesized using the sol-gel and dipping method on three different types of substrates (glass, SiO2/glass, and Si). The effect of Zn doping on the optoelectronic, microstructural, and gas-sensing properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), Raman spectroscopy, Hall effect measurements (HE), and gas testing. The results showed that the optical constants, the transmission, and the carrier numbers were correlated with the substrate type and with the microstructure and the thickness of the films. The Raman study showed the formation of ITO films and the incorporation of Zn in the doped film (ITO:Zn), which was confirmed by EDX analysis. The potential use of the multifunctional sol-gel ITO and ITO:Zn thin films was proven for TCO applications or gas-sensing experiments toward CO2. The Nyquist plots and equivalent circuit for fitting the experimental data were provided. The best electrical response of the sensor in CO2 atmosphere was found at 150 degrees C, with activation energy of around 0.31 eV.

12. The effect of noble metal addition on the properties of oxide semiconductors nanoparticles

Authors: Goncearenco, E; Morjan, IP; Dutu, E; Scarisoreanu, M; Fleaca, C; Gavrila-Florescu, L; Dumitrache, F; Banici, AM; Teodorescu, VS; Anastasescu, C; Sandulescu, A; Balint, I

Published: MAR 2022, JOURNAL OF SOLID STATE CHEMISTRY, 307, DOI: 10.1016/j.jssc.2021.122817

This work presents the preparation of W and V co-doped TiO2 nanoparticles (W:TiO2 and W:V:TiO2) using laser pyrolysis technique subsequently modified with noble metals Pt or Pd using chemical impregnation method. By using well defined TiO2 nanoparticles, the enhancement of catalytic activity is expected mainly due to their higher surface area and density defects relative to bulk material. Structural, morphological and optical properties of the as-obtained nanopowders have been characterized by transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV-VIS diffuse reflectance spectroscopy and photoluminescence techniques. The phase composition analysis reveals the preponderance of anatase (95%) in addition to ruffle phase, its particle average size ranging from 25 to 30 nm. The TiO 2 based nanomaterials were supplementary modified by noble metals deposition (Pt particles with dimensions of 3-4 nm and spherical Pd crystallites with a diameter between 3 and 9 nm) and their photocatalytic activity was tested in oxidative photo degradation of CH3OH, under simulated solar light. The metal modified samples displayed higher specific surface areas (3-6 times) and improved photocatalytic properties, the W:V:TiO2@Pt material showing better conversion efficiency of CH3OH to CH2O than the reference Degussa P25 sample (1.54 versus 0.90%).

13. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites

Authors: Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V

Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139

Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.

14. Effect of annealing on the structural, optical and electrical properties of (F, Zn) double doped SnO2 nanoparticles obtained by the laser pyrolysis method

Authors: Morjan, IP; Dutu, E; Fleaca, CT; Dumitrache, F; Morjan, I; Mihailescu, N; Demian, M; Teodorescu, VS; Scarisoreanu, M

Published: MAY 2022, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 142, 106511, DOI: 10.1016/j.mssp.2022.106511

SnO2 nanoparticles have a great potential in photocatalytic and optoelectronic applications by extending their absorbtion and emission from UV to the visible domain. The effect of annealing at 750 degrees C and 1000 degrees C for 3 h in ambient conditions on structural, optical and electrical properties of F&Zn double doped SnO2 nanoparticles synthesized by continuous wave CO2 laser pyrolysis method were investigated for the first time. X-Ray diffraction studies confirmed the expected crystallite size increasing and also the vanishing of divalent tin phases (SnF2, SnO) upon air annealing. Detailed X ray photoelectron spectroscopy (XPS) analysis confirmed that fluorine disappears completely from SnO2 structure at 1000 degrees C. The annealing also induced a reduction in oxygen vacancies as confirmed by Raman spectroscopy and XPS. Transmission FTIR spectroscopy was used for revealing the existence of Sn-O, O-Sn-O, O-H and H-O-H vibrational modes. The optical band gap energies of all annealed samples are in the visible region, decreasing for those that were initially doped with F, and increasing for the only Zn doped sample. Photoluminescence (PL) measurements showed a broad dominant peak in green visible region, around 530 nm. For the sample with the highest content of Zn, PL spectrum shifted to higher wavelengths, respectively to the orange and red regions. The oxygen vacancies concentrations after annealing are correlated with the electrical conductivity of F, F&Zn, and Zn doped SnO2 samples.

15. SiGeSn Quantum Dots in HfO2 for Floating Gate Memory Capacitors

Authors: Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Stoica, T; Ciurea, ML; Lepadatu, AM

Published: MAR 2022, COATINGS, 12, 348, DOI: 10.3390/coatings12030348

Group IV quantum dots (QDs) in HfO2 are attractive for non-volatile memories (NVMs) due to complementary metal-oxide semiconductor (CMOS) compatibility. Besides the role of charge storage centers, SiGeSn QDs have the advantage of a low thermal budget for formation, because Sn presence decreases crystallization temperature, while Si ensures higher thermal stability. In this paper, we prepare MOS capacitors based on 3-layer stacks of gate HfO2/floating gate of SiGeSn QDs in HfO2/tunnel HfO2/p-Si obtained by magnetron sputtering deposition followed by rapid thermal annealing (RTA) for nanocrystallization. Crystalline structure, morphology, and composition studies by cross-section transmission electron microscopy and X-ray diffraction correlated with Raman spectroscopy and C-V measurements are carried out for understanding RTA temperature effects on charge storage behavior. 3-layer morphology and Sn content trends with RTA temperature are explained by the strongly temperature-dependent Sn segregation and diffusion processes. We show that the memory properties measured on Al/3-layer stack/p-Si/Al capacitors are controlled by SiGeSn-related trapping states (deep electronic levels) and low-ordering clusters for RTA at 325-450 degrees C, and by crystalline SiGeSn QDs for 520 and 530 degrees C RTA. Specific to the structures annealed at 520 and 530 degrees C is the formation of two kinds of crystalline SiGeSn QDs, i.e., QDs with low Sn content (2 at.%) that are positioned inside the floating gate, and QDs with high Sn content (up to 12.5 at.%) located at the interface of floating gate with adjacent HfO2 layers. The presence of Sn in the SiGe intermediate layer decreases the SiGe crystallization temperature and induces the easier crystallization of the diamond structure in comparison with 3-layer stacks with Ge-HfO2 intermediate layer. High frequency-independent memory windows of 3-4 V and stored electron densities of 1-2 x 10(13) electrons/cm(2) are achieved.

16. Graphene/Ferroelectric (Ge-Doped HfO2) Adaptable Transistors Acting as Reconfigurable Logic Gates

Authors: Dragoman, M; Dinescu, A; Dragoman, D; Palade, C; Teodorescu, VS; Ciurea, ML

Published: JAN 2022, NANOMATERIALS, 12, 279, DOI: 10.3390/nano12020279

We present an array of 225 field-effect transistors (FETs), where each of them has a graphene monolayer channel grown on a 3-layer deposited stack of 22 nm control HfO2/5 nm Ge-HfO2 intermediate layer/8 nm tunnel HfO2/p-Si substrate. The intermediate layer is ferroelectric and acts as a floating gate. All transistors have two top gates, while the p-Si substrate is acting as a back gate. We show that these FETs are acting memtransistors, working as two-input reconfigurable logic gates with memory, the type of the logic gate depending only on the values of the applied gate voltages and the choice of a threshold current.

17. Optical, microstructural and vibrational properties of sol-gel ITO films

Authors: Nicolescu, M; Anastasescu, M; Calderon-Moreno, JM; Maraloiu, AV; Teodorescu, VS; Preda, S; Predoana, L; Zaharescu, M; Gartner, M

Published: APR 2021, OPTICAL MATERIALS, 114, DOI: 10.1016/j.optmat.2021.110999

The aim of this paper is to prepare multi-layered ITO thin films by a low cost and environmental-friendly method for different applications (optoelectronics, sensors, etc.). ITO films with 15 layers were obtained by successive depositions using the sol-gel & dip-coating method on three different substrates: glass, SiO2/glass and SiO2/Si. Comparative structural, morphological and optical characterization were performed by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Cross Section Transmission Electron Microscopy (XTEM) coupled with Selected Area Electron Diffraction (SAED), Infrared Spectroscopic Ellipsometry (IRSE) and Raman spectroscopy analyses. The optical constants (refractive index n and extinction coefficient k) were determined in a large spectral range (300-27500 cm-1) by spectroscopic ellipsometry (SE). The thicknesses determined by SE were confirmed by HRTEM (High Resolution TEM) measurements which also presents in detail the textural properties of the ITO films at nanometric level. A comparison between IRSE and Raman analysis in the infrared active region was presented.

18. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping

Authors: Palade, C; Lepadatu, AM; Slav, A; Cojocaru, O; Iuga, A; Maraloiu, VA; Moldovan, A; Dinescu, M; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: SEP 28 2021, JOURNAL OF MATERIALS CHEMISTRY C, 9, 12366, DOI: 10.1039/d1tc02921e

Orthorhombic HfO2 exhibits nanoscale ferroelectricity that opens the perspective of ultra-scalable CMOS integration of ferroelectric memories. However, many aspects of the metastable orthorhombic crystallization mechanisms still need to be elucidated and new fabrication methods are of high interest. In this paper, the atomically resolved crystal structure of HfO2 is a 3-layer structure with a Ge-rich HfO2 intermediate layer capped by a top (cap) HfO2 layer and cladded by a bottom HfO2 layer. There is a continuity of crystal growth from the top and bottom HfO2 layers into the intermediate layer. A spatial transition from a monoclinic phase to an orthorhombic phase was revealed within a region of a few atomic layers at the interface between capped and intermediate HfO2 layers. This result suggests the mechanism of orthorhombic and monoclinic phase formation by a martensitic-like transformation of the initially grown tetragonal phase. The sample fabrication method we used involved magnetron sputtering deposition of the 3-layer structures, i.e. a stack of top HfO2/Ge-rich HfO2 intermediate/bottom HfO2 layers, followed by rapid thermal annealing. It results in self-optimized orthorhombic crystallization of HfO2 by Ge nanoparticle segregation in the intermediate layer. The ferroelectric effects are revealed by polarization-voltage hysteresis loops and piezoresponse force microscopy measurements. The atomistic computations performed by using the density functional theory support the experimental results by showing that the Ge doping of HfO2 leads to orthorhombic phase stabilization and increased Berry phase polarization.

19. THERMAL BEHAVIOR OF Cu-DOPED TiO2 GELS SYNTHESIZED BY THE SOL-GEL METHOD

Authors: Pandele-Cusu, J; Atkinson, I; Rusu, A; Apostol, N; Teodorescu, V; Predoana, L; Szilagyi, IM; Pokol, G; Zaharescu, M

Published: MAR 2021, REVUE ROUMAINE DE CHIMIE, 66, 229, DOI: 10.33224/rrch.2021.66.3.01

The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by thermogravimetric and differential thermal analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) measurements. The comparative investigation of the structure and morphology of the as-prepared gels and of the nanopowders obtained by annealing them was realized by transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Significant differences were noticed depending on the amount of dopant (0.5 or 2.0 mol % CuO). A higher dopant concentration resulted in a more complex decomposition of the sample. This behavior was associated with the formation of various molecular species in the sol-gel solutions before gelation, determined by the different amount of the dopant used.

20. Advancements on Basic Working Principles of Photo-Driven Oxidative Degradation of Organic Substrates over Pristine and Noble Metal-Modified TiO2. Model Case of Phenol Photo Oxidation

Authors: Sandulescu, A; Anastasescu, C; Papa, F; Raciulete, M; Vasile, A; Spataru, T; Scarisoreanu, M; Fleaca, C; Mihailescu, CN; Teodorescu, VS; Spataru, N; Zaharescu, M; Balint, I

Published: APR 2021, CATALYSTS, 11, DOI: 10.3390/catal11040487

The specific roles played by both support and noble metals in light absorption, charge separation, and the formation of center dot OH and O-2(-) (ROS) are analyzed for light-triggered oxidation of phenol (Ph) over pristine and over noble metal (Ag, Au, Pt) -loaded TiO2. Experiments show that the supported noble metals act as a light visible absorber, assist the separation of photo-charges and reduction of O-2 to O-2(-). The O-2(-) oxidizes mildly Ph to oxygenated products (hydroquinone, benzoquinone, and 1,2-dihydroxibenzene). In a parallel process, center dot OH radicals, yielded by TiO2, mineralize Ph to CO2 by fast reaction sequences. Radical quenching and photo electrochemical measurements (surface photovoltage) confirm independently that the production of center dot OH and O-2(-) scale with oxidative conversion of Ph. The selectivity to CO2 and mild oxidation products is the result of the interplay between catalyst activity for center dot OH and for O-2(-) production.

21. Morpho-structural properties of ZnSe, TiO2-ZnSe materials and enzymatic activity of their bioinorganic hybrids with lysozyme

Authors: Anastasescu, C; Gifu, IC; Negrila, C; Socoteanu, R; Atkinson, I; Calderon-Moreno, JM; Munteanu, C; Plavan, G; Strungaru, SA; Cheatham, B; Malaroiu, AV; Teodorescu, VS; Anastasescu, M; Zaharescu, M; Balint, I; Lazarescu, V

Published: OCT 2021, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 272, DOI: 10.1016/j.mseb.2021.115350

Structural and functional changes induced by TiO2 addition to spherical zinc selenide together with lysozyme adsorption lead to valuable bioinorganic catalysts with enhanced activity. Spherical zinc selenide and its composite with TiO2 were obtained by hydrothermal method and subsequently modified by lysozyme adsorption. Morphological, structural and functional characteristics of zinc selenide based materials (ZnSe, TiO2-ZnSe) and their hybrids with lysozyme (Lys/ZnSe, Lys/TiO2-ZnSe) were investigated. TiO2 addition to ZnSe results in significant changes of surface composition, electrochemical behavior and lysozyme retention capacity. The lysozyme modified ZnSe and TiO2-ZnSe surfaces doubles the biocatalysts efficiency for 4-Methylumbelliferyl p-D-N,N',N ''-triacetylchitotrioside hydrolysis reaction compared to free lysozyme.

22. Effects of Ge-related storage centers formation in Al2O3 enhancing the performance of floating gate memories

Authors: Stavarache, I; Cojocaru, O; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: MAR 15 2021, APPLIED SURFACE SCIENCE, 542, DOI: 10.1016/j.apsusc.2020.148702

In this paper, we report studies on Al2O3/Ge/Al2O3 trilayer memory structures deposited by magnetron sputtering at room temperature on p-Si substrates coated with 3 nm SiO2. The changes of the structure, morphology and memory properties induced by rapid thermal annealing (RTA) in a broad temperature range 550-900 degrees C have been carefully investigated. High resolution transmission electron microscopy (HRTEM) revealed the existence of distinct RTA effects for different temperature ranges, in correlation with memory properties measured on Al/Al2O3/Ge/Al2O3/SiO2/p-Si/Al devices. Thus, at temperatures smaller than 650 degrees C, Ge diffuses into adjacent Al2O3, the layers remaining amorphous. The memory window increases from as-deposited samples to those annealed at 600 degrees C reaching the maximum of 5.4 V. After RTA at 700 degrees C, Ge nanocrystals (NCs) in intermediate Ge layer and Ge-rich amorphous nanoparticles in Al2O3 tunnel oxide are formed. Increasing RTA temperature to 800 and 900 degrees C, Ge NCs are no longer formed due to Ge strong diffusion. Instead, Ge-rich mixed GeAl oxide NCs of unknown crystalline structure are evidenced by HRTEM. The memory window continuously decreases with annealing temperature in the range 650-900 degrees C. The ON (OFF) charge loss of only 11% (9.8%) was found by extrapolation to 10 years.

23. Nanocrystallized Ge-Rich SiGe-HfO2 Highly Photosensitive in Short-Wave Infrared

Authors: Palade, C; Lepadatu, AM; Slav, A; Teodorescu, VS; Stoica, T; Ciurea, ML; Ursutiu, D; Samoila, C

Published: NOV 2021, MATERIALS, 14, DOI: 10.3390/ma14227040

Group IV nanocrystals (NCs), in particular from the Si-Ge system, are of high interest for Si photonics applications. Ge-rich SiGe NCs embedded in nanocrystallized HfO2 were obtained by magnetron sputtering deposition followed by rapid thermal annealing at 600 & DEG;C for nanostructuring. The complex characterization of morphology and crystalline structure by X-ray diffraction, mu-Raman spectroscopy, and cross-section transmission electron microscopy evidenced the formation of Ge-rich SiGe NCs (3-7 nm diameter) in a matrix of nanocrystallized HfO2. For avoiding the fast diffusion of Ge, the layer containing SiGe NCs was cladded by very thin top and bottom pure HfO2 layers. Nanocrystallized HfO2 with tetragonal/orthorhombic structure was revealed beside the monoclinic phase in both buffer HfO2 and SiGe NCs-HfO2 layers. In the top part, the film is mainly crystallized in the monoclinic phase. High efficiency of the photocurrent was obtained in a broad spectral range of curves of 600-2000 nm at low temperatures. The high-quality SiGe NC/HfO2 matrix interface together with the strain induced in SiGe NCs by nanocrystallization of both HfO2 matrix and SiGe nanoparticles explain the unexpectedly extended photoelectric sensitivity in short-wave infrared up to about 2000 nm that is more than the sensitivity limit for Ge, in spite of the increase of bandgap by well-known quantum confinement effect in SiGe NCs.

24. Thickness-Dependent Photoelectrochemical Water Splitting Properties of Self-Assembled Nanostructured LaFeO3 Perovskite Thin Films

Authors: Andrei, F; Ion, V; Birjega, R; Dinescu, M; Enea, N; Pantelica, D; Mihai, MD; Maraloiu, VA; Teodorescu, VS; Marcu, IC; Scarisoreanu, ND

Published: JUN 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11061371

Tuning the intrinsic structural and stoichiometric properties by different means is used for increasing the green energy production efficiency of complex oxide materials. Here, we report on the formation of self-assembled nanodomains and their effects on the photoelectrochemical (PEC) properties of LaFeO3 (LFO) epitaxial thin films as a function of layer's thickness. The variation with the film's thickness of the structural parameters such as in-plane and out-of-plane crystalline coherence length and the coexistence of different epitaxial orientation-SrTiO3// LFO, SrTiO3// LFO and [110] LFO//[10] STO, as well as the appearance of self-assembled nanodomains for film's thicknesses higher than 14 nm, is presented. LFO thin films exhibit different epitaxial orientations depending on their thickness, and the appearance of self-assembled nanopyramids-like domains after a thickness threshold value has proven to have a detrimental effect on the PEC functional properties. Using Nb:SrTiO3 as conductive substrate and 0.5 M NaOH aqueous solution for PEC measurements, the dependence of the photocurrent density and the onset potential vs. RHE on the structural and stoichiometric features exhibited by the LFO photoelectrodes are unveiled by the X-ray diffraction, high-resolution transmission electron microscopy, ellipsometry, and Rutherford backscattering spectroscopy results. The potentiodynamic PEC analysis has revealed the highest photocurrent density J(photocurrent) values (up to 1.2 mA/cm(2)) with excellent stability over time, for the thinnest LFO/Nb:SrTiO3 sample, both cathodic and anodic behavior being noticed. Noticeably, the LFO thin film shows unbiased hydrogen evolution from water, as determined by gas chromatography in aqueous 0.5 M NaOH solution under constant illumination.

25. The Influence of the Structural and Morphological Properties of WO3 Thin Films Obtained by PLD on the Photoelectrochemical Water-Splitting Reaction Efficiency

Authors: Andrei, F; Andrei, A; Birjega, R; Sirjita, EN; Radu, AI; Dinescu, M; Ion, V; Maraloiu, VA; Teodorescu, VS; Scarisoreanu, ND

Published: JAN 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11010110

Due to its physical and chemical properties, the n-type tungsten oxide (WO3) semiconductor is a suitable photoanode for water decomposition reaction. The responses of the photoelectrochemical PEC water-splitting properties as an effect of structural and optical changes of WO3 thin films, as well as the nature of electrolyte solutions, were studied in this work. The WO3 thins films have been obtained by pulsed laser deposition (PLD) on silicon (Si(001)) covered with platinum substrates using three different laser wavelengths. As the XRD (X-ray diffraction) and XTEM (cross-section transmission electron microscopy) analysis shows, the formation of highly crystalline monocline WO3 phase is formed for the film deposited at 1064 nm wavelength and poor crystalline phases with a large ordering anisotropy, characteristic of 2D structures for the films deposited at 355 nm and 193 nm wavelengths, respectively. The photogenerated current densities J(ph) depend on the laser wavelength, in both alkaline and acidic electrolyte. The maximum values of the photocurrent density have been obtained for the sample prepared with laser emitting at 355 nm. This behavior can be correlated with the coherent crystallized atomic ordering that appear for long distances (10-15 nm) in the (001) plane of the monoclinic WO3 phase structure films obtained at 355 nm laser wavelength. All the samples show poor current density in dark conditions and they are very stable in both acidic and alkaline solutions. The highest photocurrent density value is obtained in acidic solution for the WO3 thin film prepared by 355 nm laser (29 mA/cm(2) at 1.6 V vs. RHE (1.35 V vs. Ag/AgCl)).

26. GeSn/SiO2 Multilayers by Magnetron Sputtering Deposition for Short-Wave Infrared Photonics

Authors: Slav, A; Dascalescu, I; Lepadatu, AM; Palade, C; Zoita, NC; Stroescu, H; Iftimie, S; Lazanu, S; Gartner, M; Buca, D; Teodorescu, VS; Ciurea, ML; Braic, M; Stoica, T

Published: DEC 16 2020, ACS APPLIED MATERIALS & INTERFACES, 12, 56171, DOI: 10.1021/acsami.0c15887

The development of short-wave infrared (SWIR) photonics based on GeSn alloys is of high technological interest for many application fields, such as the Internet of things or pollution monitoring. The manufacture of crystalline GeSn is a major challenge, mainly because of the low miscibility of Ge and Sn. The use of embedded GeSn nanocrystals (NCs) by magnetron sputtering is a cost-effective and efficient method to relax the growth conditions. We report on the use of GeSn/SiO2 multilayer deposition as a way to control the NC size and their insulation. The in situ prenucleation of NCs during deposition was followed by ex situ rapid thermal annealing. The nanocrystallization of 20X(11nm_Ge0.865S0.135/1.5nm_SiO2) multilayers leads to formation of GeSn NCs with similar to 16% Sn concentration and similar to 9 nm size. Formation of GeSn domes that are vertically correlated contributes to the nanocrystallization process. The absorption limit of similar to 0.4 eV in SWIR found by ellipsometry is in agreement with the spectral photosensitivity. The ITO/20x(GeSn NC/SiO2)/p-Si/Al diodes show a maximum value of the SWIR photosensitivity at a reverse voltage of 0.5 V, with extended sensitivity to wavelengths longer than 2200 nm. The multilayer diodes have higher photocurrent efficiency compared to diodes based on a thick monolayer of GeSn NCs.

27. Obtaining SiGe nanocrystallites between crystalline TiO2 layers by HiPIMS without annealing

Authors: Sultan, MT; Gudmundsson, JT; Manolescu, A; Teodorescu, VS; Ciurea, ML; Svavarsson, HG

Published: MAY 1 2020, APPLIED SURFACE SCIENCE, 511, DOI: 10.1016/j.apsusc.2020.145552

Formation of SiGe nanocrystals in an oxide matrix via deposition and subsequent annealing is a widely applied approach as it gives good control over optical properties by varying the Ge atomic fraction, the size, shape and crystallinity of the nanocrystals. A common drawback of annealing is a strain relaxation in the structure creating dislocations, point defects, dangling bonds, Ge clustering and altered interface morphology. All these phenomena are well-known to degrade the optoelectronic and electrical properties of the structure. As a proof of concept, in this study we have utilized a modern technique of high impulse power magnetron sputtering (HiPIMS) to obtain a crystalline TiO2/SiGe/TiO2 structure without any pre-/post-annealing. It is furthermore demonstrated how a control of the nano-crystallite size is obtained by altering the HiPIMS discharge power alone. Grazing incidence X-ray diffraction analysis was carried out for the structural characterization, while photocurrent measurements were utilized to access the role of TiO2 structural morphology over interface integrity in determining spectral feature and sensitivity. An increase of 1 - 2 orders magnitude in spectral intensity was achieved for as-grown structures fabricated via HiPIMS in comparison to annealed structure, sputtered with conventional direct current magnetron sputtering.

28. Epitaxial GeSn Obtained by High Power Impulse Magnetron Sputtering and the Heterojunction with Embedded GeSn Nanocrystals for Shortwave Infrared Detection

Authors: Dascalescu, I; Zoita, NC; Slav, A; Matei, E; Iftimie, S; Comanescu, F; Lepadatu, AM; Palade, C; Lazanu, S; Buca, D; Teodorescu, VS; Ciurea, ML; Braic, M; Stoica, T

Published: JUL 29 2020, ACS APPLIED MATERIALS & INTERFACES, 12, 33886, DOI: 10.1021/acsami.0c06212

GeSn alloys have the potential of extending the Si photonics functionality in shortwave infrared (SWIR) light emission and detection. Epitaxial GeSn layers were deposited on a relaxed Ge buffer on Si(100) wafer by using high power impulse magnetron sputtering (HiPI-MS). Detailed X-ray reciprocal space mapping and HRTEM investigations indicate higher crystalline quality of GeSn epitaxial layers deposited by Ge HiPI-MS compared to commonly used radio frequency magnetron sputtering (RF-MS). To obtain a rectifying heterostructure for SWIR light detection, a layer of GeSn nanocrystals (NCs) embedded in oxide was deposited on the epitaxial GeSn one. Embedded GeSn NCs are obtained by cosputtering deposition of (Ge1-xSnx)(1-y)(SiO2)(y) layers and subsequent rapid thermal annealing at a low temperature of 400 degrees C. Intrinsic GeSn structural defects give p-type behavior, while the presence of oxygen leads to the n-character of the embedded GeSn NCs. Such an embedded NCs/epitaxial GeSn p-n heterostructure shows superior photoelectrical response up to 3 orders of magnitude increase in the 1.2-2.5 mu m range, as compared to performances of diode based only on embedded NCs.

29. Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe-TiO2 Films and Multilayers

Authors: Lepadatu, AM; Palade, C; Slav, A; Cojocaru, O; Maraloiu, VA; Iftimie, S; Comanescu, F; Dinescu, A; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: NOV 12 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 25053, DOI: 10.1021/acs.jpcc.0c06290

Continuous development of Si photonics requires ecological and cost-effective materials. In this work, SiGe nanocrystals (NCs) embedded in TiO2 are investigated as a photosensitive material for visible (VIS) to short-wave infrared (SWIR) broad-range detection. The TiO2 matrix has the advantage of a lower band gap than SiO2, facilitating transport of photogenerated carriers in NCs. The advantage of SiGe NCs over Ge NCs is emphasized by elucidating the mechanisms involved in rapid thermal annealing (RTA)-induced nanocrystallization. An efficiently increased NC stabilization is achieved by avoiding the detrimental fast Ge diffusion. For this, the structure, morphology, and composition were carefully characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. Two types of structures were investigated, a film of SiGe-TiO2 alloy and a multilayer of a stack of six SiGe/TiO2 pairs. The layers have been deposited on Si wafers using magnetron sputtering of Si, Ge, and TiO2 followed by RTA in an inert atmosphere. The stabilization of SiGe NCs is achieved by the formation during RTA of protective SiO2 thin layers through Si oxidation at the SiGe NC surface, acting as a barrier for Ge diffusion. Thus, embedded Ge-rich SiGe NCs are obtained, resulting in the SWIR extension of the spectral photocurrent up to 1700 nm for films and 1600 nm for multilayers. This study has shown that in multilayers, the local anisotropy of crystallization is compensated by the stress field developed in the SiGe lattice, highly visible in the bottom part. Also, SiGe crystallizes faster than TiO2 in the rutile phase, and therefore, TiO2 remains mainly amorphous.

30. SiGe nanocrystals in SiO2 with high photosensitivity from visible to short-wave infrared

Authors: Stavarache, I; Logofatu, C; Sultan, MT; Manolescu, A; Svavarsson, HG; Teodorescu, VS; Ciurea, ML

Published: FEB 24 2020, SCIENTIFIC REPORTS, 10, DOI: 10.1038/s41598-020-60000-x

Films of SiGe nanocrystals (NCs) in oxide have the advantage of tuning the energy band gap by adjusting SiGe NC s composition and size. In this study, SiGe-SiO2 amorphous films were deposited by magnetron sputtering on Si substrate followed by rapid thermal annealing at 700, 800 and 1000 degrees C. We investigated films with Si:Ge:SiO2 compositions of 25:25:50 vol.% and 5:45:50 vol.%. TEM investigations reveal the major changes in films morphology (SiGe NCs with different sizes and densities) produced by Si:Ge ratio and annealing temperature. XPS also show that the film depth profile of SiGe content is dependent on the annealing temperature. These changes strongly influence electrical and photoconduction properties. Depending on annealing temperature and Si:Ge ratio, photocurrents can be 10(3) times higher than dark currents. The photocurrent cutoff wavelength obtained on samples with 25:25 vol% SiGe ratio decreases with annealing temperature increase from 1260 nm in SWIR for 700 degrees C annealed films to 1210 nm for those at 1000 degrees C. By increasing Ge content in SiGe (5:45 vol%) the cutoff wavelength significantly shifts to 1345 nm (800 degrees C annealing). By performing measurements at 100 K, the cutoff wavelength extends in SWIR to 1630 nm having high photoresponsivity of 9.35 AW(-1).

31. Wafer-scale graphene-ferroelectric HfO2/Ge-HfO2/HfO(2)transistors acting as three-terminal memristors

Authors: Dragoman, M; Dinescu, A; Dragoman, D; Palade, C; Moldovan, A; Dinescu, M; Teodorescu, VS; Ciurea, ML

Published: DEC 4 2020, NANOTECHNOLOGY, 31, DOI: 10.1088/1361-6528/abb2bf

In this paper we report a set of experiments at the wafer level regarding field-effect transistors with a graphene monolayer channel transferred on the ferroelectric HfO2/Ge-HfO2/HfO(2)three-layer structure. This kind of transistor has a switching ratio of 10(3)between on and off states due to the bandgap in graphene induced by the ferroelectric structure. Both top and back gates effectively control the carriers' charge flow in graphene. The transistor acts as a three-terminal memristor, termed a memtransistor, with applications in neuromorphic computation.

32. SWIR photoresponse of SiGe/TiO2 multilayers with Ge-rich SiGe nanocrystals

Authors: Lepadatu, AM; Palade, C; Slav, A; Dascalescu, I; Cojocaru, O; Iftimie, S; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: 2020, CAS 2020 PROCEEDINGS: 2020 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 238, DOI:

The 1600 nm-extended SWIR photoresponse of SiGe/TiO2 multilayers with Ge-rich SiGe nanocrystals (NCs) is demonstrated. The SiGe NCs based multilayers are obtained by magnetron sputtering deposition of TiO2/ 6x(Ge/SiGe/Ge/TiO2) layers on heated p-Si substrate followed by rapid thermal annealing (RTA). Grazing incidence X-ray diffraction and Raman spectroscopy evidence the formation of cubic Ge-rich SiGe NCs and anatase TiO2. ITO/Ge-rich SiGe NCs based multilayer /p-Si heterostructure diodes, fabricated by depositing top ITO and bottom Al contacts, show n-p behavior. Photocurrent-voltage characteristics measured at 100 K under integral light illumination of reverse biased diode present a photocurrent higher with up to 2 orders of magnitude than the dark current. Spectral photocurrent increases with bias voltage increase and presents a bandgap-related cutoff wavelength of similar to 1600 nm due to the high Ge content of SiGe NCs.

33. Efficacy of annealing and fabrication parameters on photo-response of SiGe in TiO2 matrix

Authors: Sultan, MT; Gudmundsson, JT; Manolescu, A; Teodorescu, VS; Ciurea, ML; Svavarsson, HG

Published: SEP 6 2019, NANOTECHNOLOGY, 30, DOI: 10.1088/1361-6528/ab260e

SiGe nanoparticles dispersed in a dielectric matrix exhibit properties different from those of bulk and have shown great potential in devices for application in advanced optoelectronics. Annealing is a common fabrication step used to increase crystallinity and to form nanoparticles in such a system. A frequent downside of such annealing treatment is the formation of insulating SiO2 layer at the matrix/SiGe interface, degrading the optical properties of the structure. An annealing process that could bypass this downside would therefore be of great interest. In this work, a short-time furnace annealing of a SiGe/TiO2 system is applied to obtain SiGe nanoparticles without formation of the undesired SiO2 layer between the dielectric matrix (TiO2) and SiGe. The structures were prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A wide range spectral response with a response-threshold up to similar to 1300 nm was obtained, accompanied with an increase in photo-response of more than two-orders of magnitude. Scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy and grazing incidence x-ray diffraction were used to analyze the morphological changes in respective structures. Photoconductive properties were studied by measuring photocurrent spectra using applied dc-voltages at various temperatures.

34. GeSn Nanocrystals in GeSnSiO2 by Magnetron Sputtering for Short-Wave Infrared Detection

Authors: Slav, A; Palade, C; Logofatu, C; Dascalescu, I; Lepadatu, AM; Stavarache, I; Comanescu, F; Iftimie, S; Antohe, S; Lazanu, S; Teodorescu, VS; Buca, D; Ciurea, ML; Braic, M; Stoica, T

Published: JUN 2019, ACS APPLIED NANO MATERIALS, 2, +, DOI: 10.1021/acsanm.9b00571

Detection in short-wave infrared (SWIR) has become a very stringent technology requirement for developing fields like hyperspectral imaging or climate changes. In a market dominated by III-V materials, GeSn, a Si compatible semiconductor, has the advantage of cost efficiency and inerrability by using the mature Si technology. Despite the recent progress in material growth, the easy fabrication of crystalline GeSn still remains a major challenge, and different methods are under investigation. We present the formation of GeSn nanocrystals (NCs) embedded in oxide matrix and their SWIR characterization. The simple and cost-effective fabrication method is based on thermal treatment of amorphous (Ge1-xSnx)(y)(SiO2)(1-y) layers deposited by magnetron sputtering. The nanocrystallization for Ge1-xSnx with 9-22 at. % Sn composition in SiO2 matrix with 9% to 15% mole percent was studied under low thermal budget annealing in the 350-450 degrees C temperature range. While the Sn at.% content is the main parameter influencing the band-structure of the NCs, the SWIR sensitivity can be optimized by SiO2 content and H-2 gas component in the deposition atmosphere. Their role is not only changing the crystallization parameters but also to reduce the carrier recombination by passivation of NCs defects. The experiments indicate a limited composition dependent temperature range for GeSn NCs formation before beta-Sn phase segregation occurs. NCs with an average size of 6 nm are uniformly distributed in the film, except the surface region where larger GeSn NCs are formed. Spectral photovoltaic current measured on SiO2 embedded GeSn NCs deposited on p-Si substrate shows extended SWIR sensitivity up to 2.4 mu m for 15 at. % Sn in GeSn NCs. The large extension of the SWIR detection is a result of many factors related to the growth parameters and also to the in situ or ex situ annealing procedures that influence the uniformity and size distribution of NCs.

35. High performance NIR photosensitive films of Ge nanoparticles in Si3N4

Authors: Stavarache, I; Prepelita, P; Lalau, I; Cojocaru, O; Teodorescu, VS; Ciurea, ML

Published: 2019, 2019 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2019), 42ND EDITION, 228, DOI:

Films of amorphous Ge nanoparticles in Si3N4 on heated Si and quartz substrates at 300 degrees C were obtained by co-sputtering Ge, and Si3N4. The films structure and photo-electrical behaviour were studied through transmission electron microscopy and, current voltage and spectral photo-current investigations, respectively. The spectral photo-current were correlated with results obtained from transmission electron microscopy. Under illumination the current present a high increase with about one order of magnitude compared with the dark one. The photo-current spectra show a widening in near infrared to 0.97eV. Internal quantum efficiency values for -1V and 0V were determined.

36. Fabrication and characterization of Si1-xGex nanocrystals in as-grown and annealed structures: a comparative study

Authors: Sultan, MT; Maraloiu, AV; Stavarache, I; Gudmundsson, JT; Manolescu, A; Teodorescu, VS; Ciurea, ML; Svavarsson, HG

Published: SEP 17 2019, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 10, 1882, DOI: 10.3762/bjnano.10.182

Multilayer structures comprising of SiO2/SiGe/SiO2 and containing SiGe nanoparticles were obtained by depositing SiO2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high-power impulse magnetron sputtering (HiPIMS). The as-grown structures subsequently underwent rapid thermal annealing (550-900 degrees C for 1 min) in N-2 ambient atmosphere. The structures were investigated using X-ray diffraction, high-resolution transmission electron microscopy together with spectral photocurrent measurements, to explore structural changes and corresponding properties. It is observed that the employment of HiPIMS facilitates the formation of SiGe nanoparticles (2.1 +/- 0.8 nm) in the as-grown structure, and that presence of such nanoparticles acts as a seed for heterogeneous nucleation, which upon annealing results in the periodically arranged columnar self-assembly of SiGe core-shell nanocrystals. An increase in photocurrent intensity by more than an order of magnitude was achieved by annealing. Furthermore, a detailed discussion is provided on strain development within the structures, the consequential interface characteristics and its effect on the photocurrent spectra.

37. Tryptophan/Dextran70 Based-Fluorescent Silver Nanoparticles: Synthesis and Physicochemical Properties

Authors: Voicescu, M; Ionescu, S; Calderon-Moreno, JM; Teodorescu, VS; Anastasescu, M; Culita, DC

Published: JUL 2019, JOURNAL OF FLUORESCENCE, 29, 992, DOI: 10.1007/s10895-019-02411-2

Nano-size and shape of fluorescent silver nanostructures are important for a wide range of bio-applications, especially as drug delivery systems, imaging and sensing. The aim of the work is to develop a fluorescent silver nano-structured system, synthesized by chemical reduction of aqueous AgNO3 solution by Tryptophan using Dextran 70 as stabilizing agent (SNPs(FL)). The formed fluorescent nano-system was analyzed by UV-Vis absorption, DLS, SEM, TEM, AFM, steady-state and time resolved fluorescence spectroscopy. TEM analysis showed multi-twined nanoparticle, with the size within 15-40 nm. SNPs(FL) shows the fluorescence emission at 346 nm, the fluorescence quantum yield, phi = 0.034 and the integrated fluorescence lifetime, = 1.82 ns. Riboflavin fluorescence behaviour in the RF/SNPs(FL) system, has been also studied. The results have relevance in using SNPs(FL) as a potential marker/emissive system to solve various biological barriers in humans, like drug release and protein structure.

38. Ge nanoparticles in SiO2 for near infrared photodetectors with high performance

Authors: Stavarache, I; Teodorescu, VS; Prepelita, P; Logofatu, C; Ciurea, ML

Published: JUL 16 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-46711-w

In this work we prepared films of amorphous germanium nanoparticles embedded in SiO2 deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 degrees C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly dependent on the deposition temperature. In the films deposited at 300 degrees C, the Ge content is constant in the depth, while films deposited at 500 degrees C show a significant decrease of Ge content from interface of the film with substrate towards the film free surface. From the absorption curves we obtained the Ge band gap of 1.39 eV for 300 degrees C deposited films and 1.44 eV for the films deposited at 500 degrees C. The photocurrents are higher with more than one order of magnitude than the dark ones. The photocurrent spectra present different cutoff wavelengths depending on the deposition temperature, i.e. 1325 nm for 300 degrees C and 1267 nm for 500 degrees C. These films present good responsivities of 2.42 AW(-1) (52 mu W incident power) at 300 degrees C and 0.69 AW(-1) (57 mW) at 500 degrees C and high internal quantum efficiency of similar to 445% for 300 degrees C and similar to 118% for 500 degrees C.

39. Orthorhombic HfO2 with embedded Ge nanoparticles in nonvolatile memories used for the detection of ionizing radiation

Authors: Palade, C; Slav, A; Lepadatu, AM; Stavarache, I; Dascalescu, I; Maraloiu, AV; Negrila, C; Logofatu, C; Stoica, T; Teodorescu, VS; Ciurea, ML; Lazanu, S

Published: NOV 1 2019, NANOTECHNOLOGY, 30, DOI: 10.1088/1361-6528/ab352b

Trilayer memory capacitors of control HfO2/floating gate of Ge nanoparticles in HfO2/tunnel HfO2/Si substrate deposited by magnetron sputtering and subsequently annealed are investigated for the first time for applications in radiation dosimetry. In the floating gate (FG), amorphous Ge nanoparticles (NPs) are arranged in two rows inside the HfO2 matrix. The HfO2 matrix is formed of orthorhombic/tetragonal nanocrystals (NCs). The adjacent thin films to the FG are also formed of orthorhombic/tetragonal HfO2 NCs. This phase is formed during annealing, in samples with thick control HfO2, in the presence of Ge, being induced by the stress. In the rest of the control oxide, HfO2 NCs are monoclinic. Orthorhombic HfO2 has ferroelectric properties and therefore enhances the memory window produced by charge storage in Ge NPs to above 6 V. The high sensitivity of 0.8 mV Gy(-1) to a particle irradiation from a Am-241 source was measured by monitoring the flatband potential during radiation exposure after electrical writing of the memory.

40. Enhanced photoconductivity of SiGe nanocrystals in SiO2 driven by mild annealing

Authors: Sultan, MT; Manolescu, A; Gudmundsson, JT; Torfason, K; Nemnes, GA; Stavarache, I; Logofatu, C; Teodorescu, VS; Ciurea, ML; Svavarsson, HG

Published: MAR 1 2019, APPLIED SURFACE SCIENCE, 469, 878, DOI: 10.1016/j.apsusc.2018.11.061

Photosensitive films based on finely dispersed semiconductor nanocrystals (NCs) in dielectric films have great potential for sensor applications. Here we report on preparation and characterization of photosensitive Si1-xGex NCs sandwiched between SiO2 matrix. A radio-frequency magnetron sputtering was applied to obtain a multilayer-structures (MLs) by depositing SiO2/SiGe/SiO2 films on Si (0 0 1) substrate. The Si1-xGex NCs were formed by a post-deposition annealing at 100-700 degrees C for 1-5 min. The effect of annealing temperature and time on MLs morphology and NCs size and density was studied using grazing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and measurements of spectral distribution of photocurrent. It is demonstrated how the photoconductive properties of the MLs can be enhanced and tailored by controlling the NCs formation conditions and the presence of stress field in MLs and defects acting as traps and recombination centers. All these features can be adjusted/controlled by altering the annealing conditions (temperature and time). The MLs photosensitivity was increased of more than an order of magnitude by the annealing process. A mechanism, where a competition between crystallization process (NCs formation and evolution i.e. size and shapes) and stress field appearance determines the peak position in the photocurrent spectra, was identified.

41. Spherical cobalt/cobalt oxide - Carbon composite anodes for enhanced lithium-ion storage

Authors: Patrinoiu, G; Etacheri, V; Somacescu, S; Teodorescu, VS; Birjega, R; Culita, DC; Hong, CN; Calderon-Moreno, JM; Pol, VG; Carp, O

Published: FEB 20 2018, ELECTROCHIMICA ACTA, 264, 202, DOI: 10.1016/j.electacta.2018.01.098

Herein we report a simple and scalable route to synthesize porous cobalt/cobalt oxide - carbon sphere composites as anode material for rechargeable lithium-ion batteries. It involves the impregnation of starch-derived hydrochar spheres with a cobalt salt, followed by a heat treatment (700 degrees C) under inert atmosphere. The obtained high surface area (similar to 670 m(2) g(-1)), submicron spheres (similar to 300 nm diameter) with high-degree of microporosity (81%) consist of an amorphous carbon matrix with embedded Co/CoO nanoparticles (similar to 6 nm sized), having a total cobalt content of 6.2 wt%. The hybrid sphere anodes demonstrated superior specific capacity, rate performance and cycling stability. Discharge capacities of 520 and 310 mA h g(-1) are observed at charge-discharge rates of 0.1 and 1C respectively. No significant capacity fading is identified on prolonged cycling at various current densities. The electrode also demonstrated excellent structural stability during extended charge-discharge processes. (c) 2018 Elsevier Ltd. All rights reserved.

42. Enhanced photocurrent in GeSi NCs/TiO2 multilayers

Authors: Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Lazanu, S; Stoica, T; Sultan, MT; Svavarsson, HG; Ciurea, ML

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 76, DOI:

GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).

43. H2S sensing mechanism of SnO2-CuWO4 operated under pulsed temperature modulation

Authors: Simion, CE; Somacescu, S; Teodorescu, VS; Osiceanu, P; Stanoiu, A

Published: APR 15 2018, SENSORS AND ACTUATORS B-CHEMICAL, 259, 268, DOI: 10.1016/j.snb.2017.12.027

This paper reports the sensing mechanism of SnO2-CuWO4 mixed oxides towards H2S detection revealed through Pulsed Temperature Mode (PTM). After thick film deposition onto commercial substrates, the final annealing temperature enhances the material reliability through the changes occurred during the experimental conditions. PTM approach represents a tradeoff in terms of sensing mechanism versus sensing performance, in order to get insights about the fundamental aspects. The measurements have been done under dynamic gas flow conditions, in the presence of 50% relative humidity (RH). The gas sensors based on SnO2-CuWO4 exhibit sensor signals higher than 100 to 10 ppm H2S, low cross-sensitivity to common gaseous interfering agents (CO, CH4, NH3, SO2), average selective sensitivity of 8.64 towards the main interfering NO2 gas, moderate response (4 min)/recovery (5 min) transients and power consumption. In order to emphasize the role of moisture towards H2S detection mechanism, the photoacoustic spectroscopic insights were correlated with Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy results. Such approach has shown promising aspects towards further operational sensitive devices. (c) 2017 Elsevier B.V. All rights reserved.

44. Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

Authors: Mihailescu, CN; Symeou, E; Svoukis, E; Negrea, RF; Ghica, C; Teodorescu, V; Tanase, LC; Negrila, C; Giapintzakis, J

Published: APR 25 2018, ACS APPLIED MATERIALS & INTERFACES, 10, 14144, DOI: 10.1021/acsami.8b01436

Controlling the semiconductor-to-metal transition temperature in epitaxial VO2 thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO2 epitaxial thin films grown on TiO2 substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V4+-V4+ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO2/TiO2 multilayer structures.

45. Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting

Authors: Haydous, F; Scarisoreanu, ND; Birjega, R; Ion, V; Lippert, T; Dumitrescu, N; Moldovan, A; Andrei, A; Teodorescu, VS; Ghica, C; Negrea, R; Dinescu, M

Published: OCT 25 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-34010-9

We report significant photoelectrochemical activity of Y-doped BiFeO3 (Y-BFO) epitaxial thin films deposited on Nb: SrTiO3 substrates. The Y-BFO photoanodes exhibit a strong dependence of the photocurrent values on the thickness of the films, and implicitly on the induced epitaxial strain. The peculiar crystalline structure of the Y-BFO thin films and the structural changes after the PEC experiments have been revealed by high resolution X-ray diffraction and transmission electron microscopy investigations. The crystalline coherence breaking due to the small ionic radius Y-addition was analyzed using Willliamson-Hall approach on the 2 theta-omega scans of the symmetric (00l) reflections and confirmed by high resolution TEM (HR-TEM) analysis. In the thinnest sample the lateral coherence length (L-parallel to) is preserved on larger nanoregions/ nanodomains. For higher thickness values L-parallel to is decreasing while domains tilt angles (alpha(tilt)) is increasing. The photocurrent value obtained for the thinnest sample was as high as J(ph) = 0.72 mA/cm(2), at 1.4 V(vs. RHE). The potentiostatic scans of the Y-BFO photoanodes show the stability of photoresponse, irrespective of the film's thickness. There is no clear cathodic photocurrent observation for the Y-BFO thin films confirming the n-type semiconductor behavior of the Y-BFO photoelectrodes.

46. Enhanced photocurrent in GeSi NCs / TiO2 multilayers

Authors: Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Lazanu, S; Stoica, T; Sultan, MT; Svavarsson, HG; Ciurea, ML

Published: 2018, , DOI:

47. Networked mesoporous SnO2 nanostructures templated by Brij (R) 35 with enhanced H2S selective performance

Authors: Stanoiu, A; Simion, CE; Sackmann, A; Baibarac, M; Florea, OG; Osiceanu, P; Teodorescu, VS; Somacescu, S

Published: NOV 1 2018, MICROPOROUS AND MESOPOROUS MATERIALS, 270, 101, DOI: 10.1016/j.micromeso.2018.05.008

Sensors based networked mesoporous SnO2 nanostructures templated by non-ionic surfactant - Brij (R) 35 were prepared via hydrothermal chemistry route. Specific patterns of the structure, morphology, surface chemistry and sensing properties were obtained by pH and autogenous pressure tuning. Consequently, the as-obtained SnO2 powders were subjected to extensive BET, Raman, TEM, HRTEM and XPS complementary investigations. The sensitive films were obtained by screen printing deposition of the powders onto commercial Al2O3 substrates. The gas sensing properties were assessed towards different hazardous gas species: CO, CH4, NH3, NO2, SO2 and H2S over a wide range of operating temperatures. Our particular SnO2 HP sensor synthesized at high autogenous pressure showed the highest selective-sensitivity to H2S (< 5 ppm) under 50% relative humidity (RH). The enhancement in the H2S sensitivity at low operating temperature under infield conditions was found to be closely connected to the morphological aspects and surface chemistry, peculiarities that can be assessed as consequences of the chemical tuning.

48. Material parameters from frequency dispersion simulation of floating gate memory with Ge nanocrystals in HfO2

Authors: Palade, C; Lepadatu, AM; Slav, A; Lazanu, S; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: JAN 15 2018, APPLIED SURFACE SCIENCE, 428, 702, DOI: 10.1016/j.apsusc.2017.09.038

Trilayer memory capacitors with Ge nanocrystals (NCs) floating gate in HfO2 were obtained by magnetron sputtering deposition on p-type Si substrate followed by rapid thermal annealing at relatively low temperature of 600 degrees C. The frequency dispersion of capacitance and resistance was measured in accumulation regime of Al/HfO2 gate oxide/Ge NCs in HfO2 floating gate/HfO2 tunnel oxide/SiOx/p-Si/Al memory capacitors. For simulation of the frequency dispersion a complex circuit model was used considering an equivalent parallel RC circuit for each layer of the trilayer structure. A series resistance due to metallic contacts and Si substrate was necessary to be included in the model. A very good fit to the experimental data was obtained and the parameters of each layer in the memory capacitor, i.e. capacitances and resistances were determined and in turn the intrinsic material parameters, i.e. dielectric constants and resistivities of layers were evaluated. The results are very important for the study and optimization of the hysteresis behaviour of floating gate memories based on NCs embedded in oxide. (C) 2017 Published by Elsevier B.V.

49. GeSi nanocrystals in SiO2 matrix with extended photoresponse in near infrared

Authors: Stavarache, I; Nedelcu, L; Teodorescu, VS; Maraloiu, VA; Dascalescu, I; Ciurea, ML

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 256, DOI:

The films of SiGe nanocrystals in SiO2 on Si substrate were obtained by co-sputtering Si, Ge, and SiO2 followed by rapid thermal annealing. The films structure and morphology together with electrical and photoelectrical properties were studied by x-ray diffraction, transmission electron microscopy, current - voltage and spectral photocurrent measurements. The photocurrent spectra at 300, 200 and 100 K were correlated with results obtained from X-ray diffractograms and transmission electron microscopy. The photocurrent spectra show an extension in near infrared due to the enriching SiGe nanocrystals in Ge.

50. H2S selective sensitivity of Cu doped BaSrTiO3 under operando conditions and the associated sensing mechanism

Authors: Stanoiu, A; Piticescu, RM; Simion, CE; Rusti-Ciobota, CF; Florea, OG; Teodorescu, VS; Osiceanu, P; Sobetkii, A; Badilita, V

Published: JUL 1 2018, SENSORS AND ACTUATORS B-CHEMICAL, 264, 336, DOI: 10.1016/j.snb.2018.03.013

Nanostructured Cu mol. 5% doped perovskite material Ba0.75Sr0.25TiO3 was synthesized under hydrothermal conditions and further on deposited via RF sputtering technique onto commercial Al2O3 substrates provided with Au interdigital electrodes and Pt heater. The obtained thin films have been analyzed by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), X-ray photoelectron spectroscopy (XPS), Differential Scanning Calorimetry-Thermogravimetry (DSC-TG) and electrical investigations. The H2S (5-90 ppm) gas-surface interaction at moderate operating temperature (T-op = 250 degrees C) associated with the interplay between the pre-adsorbed oxygen species and surface dipolar hydroxyl groups, has been highlighted by simultaneous work function and electrical resistance measurements. By correlation with the XPS spectra, the dominant role of surface hydroxylation was revealed and the subsequent gas sensing mechanism under operando conditions has been addressed. (C) 2018 Elsevier B.V. All rights reserved.

51. Influence of preparation conditions on structure and photosensing properties of GeSi/TiO2 multilayers

Authors: Slav, A; Palade, C; Stavarache, I; Teodorescu, VS; Ciurea, ML; Muller, R; Dinescu, A; Sultan, MT; Manolescu, A; Gudmundsson, JT; Svavarsson, HG

Published: 2017, 2017 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 40TH EDITION, 66, DOI:

The photosensing properties related to the structure of GeSi/TiO2 multilayers prepared under different conditions are studied. TiO2 cap/(GeSi/TiO2)(2) multilayers (ML) were deposited by magnetron sputtering (MS) and annealed by rapid thermal annealing. Trilayers of TiO2 cap/GeSi/TiO2 (TL) were also deposited using reactive high power impulse MS (HiPIMS) for TiO2 layers and dc MS for the GeSi layer. For TL samples a two-step annealing was employed, one before and the second after depositing TiO2 cap. Structure and morphology characterization (X-ray diffraction, scanning and transmission electron microscopy) was carried out and photocurrent measurements (voltage dependences, spectral curves) were performed. The annealed ML samples are formed of GeSi NCs with 5 - 10 nm sizes, while in the annealed TL samples, the GeSi NCs are larger (20 - 30 nm). These morphologies determine the multilayers photosensing properties in VIS-NIR of ML structures and in UV in TL ones, respectively.

52. Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors

Authors: Lepadatu, AM; Palade, C; Slav, A; Maraloiu, AV; Lazanu, S; Stoica, T; Logofatu, C; Teodorescu, VS; Ciurea, ML

Published: APR 28 2017, NANOTECHNOLOGY, 28, DOI: 10.1088/1361-6528/aa66b7

High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO2/floating gate of single layer of Ge QDs in HfO2/tunnel HfO2/p-Si wafers. Both Ge and HfO2 are nanostructured by RTA at moderate temperatures of 600-700 degrees C. By nanostructuring at 600 degrees C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 x 1015 m(-2) is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO2 NCs boundaries, while another part of the Ge atoms is present inside the HfO2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8. +/-. 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO2, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

53. Synthesis, physicochemical characterization and cytotoxic properties of riboflavin loaded Myrj52-silver nanoparticles

Authors: Voicescu, M; Ionescu, S; Craciunescu, O; Tatia, R; Moldovan, L; Teodorescu, VS; Nistor, CL

Published: JUL 7 2017, NEW JOURNAL OF CHEMISTRY, 41, 5541, DOI: 10.1039/c7nj00571g

The synthesis and physicochemical characterization of riboflavin (RF) loaded Myrj52-silver nanoparticles (SNPs) were performed and their cytotoxic properties were evaluated. Transmission electron microscopy analysis showed the formation of colloidal spherical SNPs with an average size of similar to 12 nm. The structure, stability, dynamics and conformation of human serum albumin (HSA) binding RF on SNPs have been studied. The influence of RF on the secondary structure of HSA in the presence of SNPs showed a predominant alpha-helix structure (61.7%). No changes induced by RF binding to HSA were observed. The cytotoxicity of RF and RF-HSA loaded Myrj52-SNPs was evaluated in vitro using the Neutral Red assay and cell morphology observations in a culture of L929 fibroblast cells. The results have relevance with regard to the RF loaded Myrj52-SNP formulation for pharmaceuticals.

54. Sensors based on mesoporous SnO2-CuWO4 with high selective sensitivity to H2S at low operating temperature

Authors: Stanoiu, A; Simion, CE; Calderon-Moreno, JM; Osiceanu, P; Florea, M; Teodorescu, VS; Somacescu, S

Published: JUN 5 2017, JOURNAL OF HAZARDOUS MATERIALS, 331, 160, DOI: 10.1016/j.jhazmat.2017.02.038

Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N-2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100 degrees C) reaches values from 10(5) (for SnWCu600) to 10(6) (for SnWCu800) over the full range of concentrations (5-30 ppm). The recovery processes were induced by a short temperature trigger of 500 degrees C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH). (C) 2017 Elsevier B.V. All rights reserved.

55. Photosensitive GeSi/TiO2 multilayers in VIS-NIR

Authors: Palade, C; Dascalescu, I; Slav, A; Lepadatu, AM; Lazanu, S; Stoica, T; Teodorescu, VS; Ciurea, ML; Comanescu, F; Muller, R; Dinescu, A; Enuica, A

Published: 2017, 2017 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 40TH EDITION, 70, DOI:

The electrical and photosensing properties correlated with structure and morphology of TiO2/(GeSi/TiO2)(2) multilayers are investigated. The multilayers are prepared by magnetron sputtering followed by rapid thermal annealing. Studies of Raman spectroscopy, transmission electron microscopy and X-ray diffraction are carried out. Measurements of dark current versus voltage and temperature are done. The photosensing properties are studied by measuring photocurrent spectra at different temperatures. We obtain multilayers with 10 - 15 nm Ge0.6Si0.4 nanocrystals (NCs) by annealing at 800 degrees C. We evidence the tunneling mechanism between neighbor NCs (T-1/2 law) in the dark current-temperature dependence. The photocurrent spectrum has a maximum with position shifting from 940 to 980 nm when the measurement temperature increases from 150 to 300 K, being due to the GeSi NCs.

56. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

Authors: Scarisoreanu, ND; Craciun, F; Birjega, R; Ion, V; Teodorescu, VS; Ghica, C; Negrea, R; Dinescu, M

Published: MAY 9 2016, SCIENTIFIC REPORTS, 6, DOI: 10.1038/srep25535

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (epsilon' similar to 2500) and low dielectric loss (tan delta < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target.

57. Multiscale investigation of USPIO nanoparticles in atherosclerotic plaques and their catabolism and storage in vivo

Authors: Maraloiu, VA; Appaix, F; Broisat, A; Le Guellec, D; Teodorescu, VS; Ghezzi, C; van der Sanden, B; Blanchin, MG

Published: JAN 2016, NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE, 12, 200, DOI: 10.1016/j.nano.2015.08.005

The storage and catabolism of Ultrasmall SuperParamagnetic Iron Oxide (USPIO) nanoparticles were analyzed through a multiscale approach combining Two Photon Laser Scanning Microscopy (TPLSM) and High-Resolution Transmission Electron Microscopy (HRTEM) at different times after intravenous injection in an atherosclerotic ApoE(-/-) mouse model. The atherosclerotic plaque features and the USPIO heterogeneous biodistribution were revealed down from organ's scale to subcellular level. The biotransformation of the nanoparticle iron oxide (maghemite) core into ferritin, the non-toxic form of iron storage, was demonstrated for the first time ex vivo in atherosclerotic plaques as well as in spleen, the iron storage organ. These results rely on an innovative spatial and structural investigation of USPIO's catabolism in cellular phagolysosomes. This study showed that these nanoparticles were stored as non-toxic iron compounds: maghemite oxide or ferritin, which is promising for MRI detection of atherosclerotic plaques in clinics using these USPIOs. From the Clinical Editor: Advance in nanotechnology has brought new contrast agents for clinical imaging. In this article, the authors investigated the use and biotransformation of Ultrasmall Super-paramagnetic Iron Oxide (USPIO) nanoparticles for analysis of atherosclerotic plagues in Two Photon Laser Scanning Microscopy (TPLSM) and High-Resolution Transmission Electron Microscopy (HRTEM). The biophysical data generated from this study could enable the possible use of these nanoparticles for the benefits of clinical patients. (C) 2015 Elsevier Inc. All rights reserved.

58. AMMONIA SENSING WITH 5 MOL% LANTHANUM DOPED BARIUM STRONTIUM TITANATE UNDER HUMID AIR BACKGROUND

Authors: Simion, CE; Stanoiu, A; Teodorescu, VS; Rusti, CF; Piticescu, RM; Vasile, E; Vasile, E; Tudor, IA

Published: FEB 2016, REVUE ROUMAINE DE CHIMIE, 61, +, DOI:

Nanostructured Ba0.7Sr0.3TiO3 (BST) with 5 molar % of Lanthanum (La) have been synthesized using a high pressure hydrothermal chemical route. The structural and morphological investigations were performed. Termogravimetry/differential scanning calorimetry and Raman investigations have been also employed to analyse the as-prepared material. The gas sensing investigations have indicated the ability of La doped BST to detect ammonia, when operated at room temperature in humid background. The obtained results were discussed with respect to the possible gas-sill-face interaction mechanism. In addition, the said material showed low cross-sensitivity to other possible interfering gases: methane, carbon monoxide, nitrogen dioxide, sulphur dioxide and hydrogen sulphide.

59. Thermal analysis of repa-germanium (Ge-132)

Authors: Batalu, D; Paun, A; Ferbinteanu, M; Aldica, G; Vlaicu, AM; Teodorescu, VS; Badica, P

Published: NOV 20 2016, THERMOCHIMICA ACTA, 644, 27, DOI: 10.1016/j.tca.2016.10.005

Thermal behavior of repa-germanium (C6H10Ge2O7, Ge-132) during heating in air or in argon is investigated using DSC-TGA, XRD, SEM,TEM, and FT-IR measurements. Nine domains of thermal transformations were identified from room temperature to 1200 degrees C, in air or argon. The first reversible transformation is below 220 degrees C and it was assigned to an isomerization process, based on DSC, XRD and IR measurements. The next five transformation domains (220-910 degrees C) are decompositions accompanied by weight loss. The main product of thermal decomposition is Ge. The next transformation domain (910-970 degrees C) corresponds to melting of Ge, both in argon and air. In the air, this step is followed by oxidation of Ge (970-1100 degrees C) and, finally, by melting of GeO2. Amorphous phases formed between 220 and 720 degrees C. Observed processes are discussed based on crystal chemistry and bonds dynamics considerations. (C) 2016 Elsevier B.V. All rights reserved.

60. Ultra-Thin Epitaxial Tungsten Carbide Schottky Contacts in 4H-SiC

Authors: Knoll, L; Teodorescu, V; Minamisawa, RA

Published: OCT 2016, IEEE ELECTRON DEVICE LETTERS, 37, 1320, DOI: 10.1109/LED.2016.2604488

We demonstrate the fabrication and characterization of epitaxial W2C Schottky contacts into 4H-SiC via sputtering deposition of ultra-thin W followed by thermal annealing. The alloying reaction occurs below 600 degrees C, yielding a stable layer up to 1200 degrees C. The epitaxial layer is hexagonal, unexpectedly forming W2C phase even at the lowest annealing temperature, which is predicted to occur at 1500 degrees C in bulk systems. Schottky contacts based on epitaxial W2C films exhibit smoother interface morphology, higher thermal stability, lower turn-ON voltage and about similar to 50% reduction in Schottky-contact resistance compared with thick Ti Schottky contacts.

61. How morphology determines the charge storage properties of Ge nanocrystals in HfO2

Authors: Slav, A; Palade, C; Lepadatu, AM; Ciurea, ML; Teodorescu, VS; Lazanu, S; Maraloiu, AV; Logofatu, C; Braic, M; Kiss, A

Published: MAR 1 2016, SCRIPTA MATERIALIA, 113, 138, DOI: 10.1016/j.scriptamat.2015.10.028

The strong correlation between morphology and charge storage properties of HfO2/Ge/HfO2/Si trilayer structures was evidenced. The morphology of structures deposited by magnetron sputtering and electron beam evaporation was tailored by rapid thermal annealing and investigated by transmission electron microscopy, Raman and X-ray photoelectron spectroscopies. The best hysteresis loops (capacitance-voltage characteristics) were obtained for trilayers with high density Ge nanocrystals located in the position of as-deposited Ge layer. The decrease of Ge nanocrystals density narrows the memory window, by spreading Ge atoms into HfO2 matrix (sputtered trilayers), or by Ge atoms expulsion toward HfO2 nanocrystals surface (evaporated trilayers). (C) 2015 Elsevier Ltd. All rights reserved.

62. Low level NO2 detection under humid background and associated sensing mechanism for mesoporous SnO2

Authors: Stanoiu, A; Somacescu, S; Calderon-Moreno, JM; Teodorescu, VS; Florea, OG; Sackmann, A; Simion, CE

Published: AUG 2016, SENSORS AND ACTUATORS B-CHEMICAL, 231, 174, DOI: 10.1016/j.snb.2016.02.137

Mesoporous SnO2 prepared by a hydrothermal synthesis route assisted by the ionic surfactant Cetyltrimethylammonium bromide, has rutile-type tetragonal symmetry, small homogeneous nanocrystallite size of similar to 4 nm and good thermal stability. Porosity analysis revealed high surface area similar to 127 m(2)/g and a narrow pore size distribution, with an average pore diameter similar to 4 nm. The mesoporous structure is likewise advantageous towards enhancing the surface reactivity and subsequent gas sensing performances. The role played by the surface hydroxylation on the NO2 sensing mechanism was discussed with respect to the associated photoelectron spectral components. Under humid air, associated with the in-field conditions, the highest sensitivity was attained at 150 degrees C, were the sensor signal towards NO2 is 4 times higher than the one recorded in dry air. This feature has been experimentally demonstrated by simultaneous electrical resistance and work function changes measurements conducted in the range of 400-5000 ppb NO2. (C) 2016 Elsevier B.V. All rights reserved.

63. Structural and electrical properties of Nb doped TiO2 films prepared by the sol-gel layer-by-layer technique

Authors: Duta, M; Simeonov, S; Teodorescu, V; Predoana, L; Preda, S; Nicolescu, M; Marin, A; Spasov, D; Gartner, M; Zaharescu, M; Szekeres, A

Published: FEB 2016, MATERIALS RESEARCH BULLETIN, 74, 20, DOI: 10.1016/j.materresbull.2015.10.009

Thin films of 5 and 10-layered sol gel TiO2 were doped with 1.2 at.% Nb and their structural, optical and electrical properties were investigated. The films crystallized only in anatase phase, as evidenced by X-ray diffraction and selected area electron diffraction analyses. High resolution transmission electron microscopy revealed nanosized crystallites with amorphous boundaries. Current-voltage measurements on metal-TiO2 Si structures showed the formation of ri+ n heterojunction at the TiO2-Si interface with a rectification ratio of 10(4). The effective donor density varies between 10(16) and 10(17) cm(-3), depending on film thickness. The sheet energy densities under forward and reverse bias are in the order of 10(12) and 10(10) cm(-2) respectively. These values and the high specific resistivity (10(4) Omega cm) support the existence of compensating acceptor levels in these films. It was established that the conduction mechanism is based on space charge limited current via deep levels with different energy positions in the band gap. (C) 2015 Elsevier Ltd. All rights reserved.

64. High atomic diffusivity during pulsed laser irradiation of TiON quasi-amorphous films

Authors: Teodorescu, VS; Maraloiu, AV; Negrea, RF; Ghica, D; Scarisoreanu, ND; Dinescu, M; Gartner, M; Blanchin, MG

Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 251, DOI: 10.1016/j.apsusc.2015.11.188

Quasi-amorphous titanium oxynitride (TiON) films were obtained by annealing sol-gel anatase TiO2 films in NH3 atmosphere at 600 degrees C. These films were irradiated with 50 laser pulses using the fourth harmonic (266 nm) radiation of the Nd-YAG laser, with an average fluence of 20 mJ/cm(2). HRTEM observations of the pulsed laser irradiated films evidenced the rutile TiO2 nanocrystallites formation. The rutile structure was not present either in the TiON films before the laser irradiation, or in the initial sol-gel anatase TiO2 films. During the laser irradiation, the film structure remains in the solid state phase, as it results from the temperature estimation and microscopic observations. For the rutile nanocrystals formation, the atomic diffusion length of the oxygen and titanium atoms should be in the nanometric range during the laser pulse action, which implies a diffusivity close to the values observed in the liquid phase. We consider that the rutile phase formation is a proof of the fast atomic diffusion in the solid amorphous matrix, during the laser irradiation. (C) 2015 Published by Elsevier B.V.

65. Non-volatile memory structures with Ge NCs-HfO2 intermediate layer

Authors: Palade, C; Slav, A; Lepadatu, AM; Maraloiu, AV; Lazanu, S; Logofatu, C; Teodorescu, VS; Ciurea, ML

Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 166, DOI:

The structure and charge storage properties of a trilayer structure with Ge nanocrystals embedded in HfO2 oxide were studied. The trilayer structure HfO2/Ge-HfO2/HfO2/p-Si was prepared by magnetron sputtering and subsequent rapid thermal annealing at 600 degrees C. The TEM investigations reveal the formation of Ge NCs embedded in crystalline HfO2 at the position of the Ge-HfO2 layer. The capacitors were made by Al evaporation on both front and backside of the trilayer structure. The C-V characteristics show a counterclockwise hysteresis with large memory window of 0.85 V which is given only by the contribution of the Ge NCs embedded in HfO2. The I-V characteristics show an asymmetric behavior, the currents are three times higher for the negative voltage than the positive one.

66. Fast atomic diffusion in amorphous films induced by laser pulse annealing

Authors: Teodorescu, VS; Ghica, C; Maraloiu, AV; Kuncser, A; Lepadatu, AM; Stavarache, I; Ciurea, ML; Scarisoreanu, ND; Andrei, A; Dinescu, M

Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 158, DOI:

Fast atomic diffusion was evidenced in the surface layer of amorphous thin films of oxides and semiconductors irradiated with low fluence UV pulse laser. This process takes place in a surface layer with a thickness related to the laser radiation absorption depth in the target material and was revealed by the cross section transmission electron microscopy studies. These high values of diffusivity can be explained by supposing the glass transition transformation in the amorphous structure, triggered by the action of the laser pulse field. This effect can have application for controlling structural modifications at nanoscale of the thin films surface and also for inducing structural modification of interfaces between the film and substrate.

67. Characterization of a n+3C/n-4H SiC heterojunction diode

Authors: Minamisawa, RA; Mihaila, A; Farkas, I; Teodorescu, VS; Afanas'ev, VV; Hsu, CW; Janzen, E; Rahimo, M

Published: APR 4 2016, APPLIED PHYSICS LETTERS, 108, DOI: 10.1063/1.4945332

We report on the fabrication of n+3C/n-4H SiC heterojunction diodes (HJDs) potentially promising the ultimate thermal stability of the junction. The diodes were systematically analyzed by TEM, X-ray diffraction, AFM, and secondary ion mass spectroscopy, indicating the formation of epitaxial 3C-SiC crystal on top of 4H-SiC substrate with continuous interface, low surface roughness, and up to similar to 7 x 10(17) cm(-3) dopant impurity concentration. The conduction band off-set is about 1 V as extracted from CV measurements, while the valence bands of both SiC polytypes are aligned. The HJDs feature opening voltage of 1.65 V, consistent with the barrier height of about 1.5 eV extracted from CV measurement. We finally compare the electrical results of the n+3C/n-4H SiC heterojunction diodes with those featuring Si and Ge doped anodes in order to evaluate current challenges involved in the fabrication of such devices. (C) 2016 AIP Publishing LLC.

68. HfO2 with embedded Ge nanocrystals with memory effects

Authors: Palade, C; Slav, A; Lepadatu, AM; Maraloiu, AV; Teodorescu, VS; Ciurea, ML

Published: 2015, 2015 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 48, DOI:

The charge storage properties of Ge nanocrystals-based MOS-like capacitors with tunnel and gate HfO2 are studied. HfO2/Ge/HfO2/Si trilayer structures were prepared by magnetron sputtering (in Ar) and subsequent rapid thermal annealing (650 degrees C). HfO2/Si structures were also prepared, some under similar conditions, while others were deposited in Ar:O-2. TEM investigations and C-V measurements were performed. TEM on annealed trilayers evidences the formation of ordered and precisely positioned array of Ge nanocrystals embedded in crystalline HfO2. The annealed Al/HfO2/Ge/HfO2/p-Si/Al capacitors present counterclockwise C-V hysteresis (0.8 V memory window) mainly given by Ge nanocrystals, with negligible contribution from crystallized-HfO2 traps.

69. Atomic scale elemental mapping of light elements in multilayered perovskite coatings

Authors: Negrea, RF; Teodorescu, VS; Ghica, C

Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 255, DOI: 10.1016/j.apsusc.2015.07.106

Spherical aberration corrected transmission electron microscopes offer unprecedented capabilities in materials structural characterization down to atomic resolution. Electron energy loss spectroscopy (EELS) - spectrum imaging (SI) and annular bright field (ABF) imaging allow to simultaneously identify both the position and nature of the atomic species in a crystalline material. These techniques, along with conventional high-resolution transmission electron microscopy are particularly useful in heterostructures interfaces like epitaxial multilayers characterization, for identifying possible atomic interdiffusion at sub-nanometric scale. This paper presents the structural and compositional microanalysis down to atomic resolution of an epitaxial BaTiO3/SrRuO3/SrTiO3 ferroelectric heterostructure using complex complementary analytical electron microscopy techniques. The atomic arrangement of both heavy and light atomic species across the interfaces in the BaTiO3/SrRuO3/SrTiO3 heterostructures is revealed. (C) 2015 Elsevier B.V. All rights reserved.

70. Nanostructuring of GeTiO amorphous films by pulsed laser irradiation

Authors: Teodorescu, VS; Ghica, C; Maraloiu, AV; Vlaicu, M; Kuncser, A; Ciurea, ML; Stavarache, I; Lepadatu, AM; Scarisoreanu, ND; Andrei, A; Ion, V; Dinescu, M

Published: APR 7 2015, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 6, 900, DOI: 10.3762/bjnano.6.92

Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 degrees C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.

71. NIR to Vis - NIR up - conversion and X-ray excited emission of Er doped high Z BiOCl

Authors: Avram, D; Cojocaru, B; Florea, M; Teodorescu, V; Tiseanu, I; Tiseanu, C

Published: MAY 1 2015, OPTICAL MATERIALS EXPRESS, 5, 962, DOI: 10.1364/OME.5.000951

Herein, we investigate the emission properties of Er - BiOCl in the range of similar to 500 to 1700 nm under down - (488 and 973 nm) and NIR (telecom - wavelength at similar to 1500 nm) up - conversion excitation as well high energy X-ray excitation. The dependencies of red (similar to 670 nm) and NIR (similar to 800 nm) to green emission (similar to 543 nm) ratio with Er concentration, excitation mode and delay after laser pulse as well as the up - conversion excitation spectra and decays are analyzed in terms of competitive ground state absorption/excited state absorption and energy transfer up - conversion mechanisms. The CIE chromaticity diagram show single excitation (similar to 1500 nm), delay induced emission color change from yellowish green (delay of 0.001 ms) to reddish orange (delay of 1 ms). The X-ray induced emission of Er - BiOCl presents an atypical red to green emission ratio that exceeds that measured under optical down - conversion excitation by a factor of 13. The potential of Er - BiOCl for optical/X-ray imaging applications is discussed. (C)2015 Optical Society of America

72. On the photocatalytic reduction of MU tetrazolium salt on the surface of TiO2 nanoparticles: Formazan production kinetics and mechanism

Authors: Popescu, T; Lupu, AR; Raditoiu, V; Purcar, V; Teodorescu, VS

Published: NOV 1 2015, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 457, 120, DOI: 10.1016/j.jcis.2015.07.005

Hypothesis: The MU [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide] cell cytotoxicity indicator is photocatalytically reduced on the surface of TiO2 nanoparticles in phosphate-buffered-saline (PBS) environment. We hypothesize that specific phosphate adsorption may be used to modulate the efficiency of the TiO2 MU reaction through colloidal and semiconductor-liquid interface processes. Experiments: The TiO2 MU reaction kinetics was studied in PBS, with respect to photocatalyst and MIT concentrations and irradiation wavelength. The effects of PBS and electron scavengers (Fe3+ ions) on reaction efficiency and the role of colloidal surface charge in the photocatalytic process were investigated. The structural and spectroscopic characteristics of relevant TiO2-formazan systems were studied by X-ray diffraction, transmission electron microscopy and IR-spectroscopy. Findings: The reaction was pseudo-first order with respect to photocatalyst and showed a negative and fractional partial order with respect to MU. Formazan production rates were directly proportional to radiation wavelength and TiO2 concentration and inversely proportional to the MIT initial concentration. The addition of Fe3+ ions, as well as the absence of PBS, induced strong reaction inhibition. Reaction efficiency and catalyst Zeta potential were enhanced by Na2HPO4 (PBS component) and showed a maximum around the phosphate concentration 0.005 M. Findings: Structural/spectroscopic characterization confirmed the formation of amorphous MU-formazan on the surface of TiO2 and the TiO2-phosphate binding. (C) 2015 Elsevier Inc. All rights reserved.

73. Synthesis of Copper Particles by Non-thermal Atmospheric Pressure Plasma Jet

Authors: Lazea-Stoyanova, A; Vlad, A; Vlaicu, AM; Teodorescu, VS; Dinescu, G

Published: AUG 2015, PLASMA PROCESSES AND POLYMERS, 12, 709, DOI: 10.1002/ppap.201400197

The present study reveals the synthesis of metallic particles at atmospheric pressure using a radiofrequency low-temperature argon plasma jet. Copper bulk material of the powered electrode acted as solid precursor in the process and the metallic particles were obtained directly in gaseous environment. The particles were collected onto Si (100)-oriented substrates downstream of the atmospheric plasma jet and were ex situ characterized via optical microscopy, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. We obtained copper particles, reddish brown in color, either of nano-or micro-metric sizes. Additionally, the plasma species and gas temperature were determined by OES. In conclusion, it was demonstrated that conversion of bulk metals into particles is possible at atmospheric pressure using a radiofrequency plasma jet and the development of several applications is recommended.

74. Room temperature ammonia sensing with barium strontium titanate under humid air background

Authors: Simion, CE; Sackmann, A; Teodorescu, VS; Rusti, CF; Stanoiu, A

Published: DEC 1 2015, SENSORS AND ACTUATORS B-CHEMICAL, 220, 1246, DOI: 10.1016/j.snb.2015.07.045

Within the field of chemical gas sensing, ammonia detection represents one of the nowadays challenges, due to its adverse effects for human health. Real operating investigations are imposed by the high solubility potential of NH3 at room temperature. Thick films of Ba0.75Sr0.25TiO3 material have been investigated by means of electrical resistance and capacitance changes and correlated with the photoacoustic outputs. The experimental findings have been discussed in terms of Grotthuss mechanism, with respect to the ionic/electronic conduction within BST, toward ammonia detection enhanced by the presence of water vapors when operated at room temperature. So an appropriate NH3 sensing mechanism was proposed. (C) 2015 Elsevier B.V. All rights reserved.

75. Structural, magnetic and catalytic properties of cobalt chromite obtained through precursor method

Authors: Gingasu, D; Mindru, I; Culita, DC; Patron, L; Calderon-Moreno, JM; Osiceanu, P; Preda, S; Oprea, O; Parvulescu, V; Teodorescu, V; Walsh, JPS

Published: FEB 2015, MATERIALS RESEARCH BULLETIN, 62, 64, DOI: 10.1016/j.materresbull.2014.11.009

Cobalt chromite (CoCr2O4) was synthesized through the precursor method. The precursors: (NH4)(3)[CoCr2(C4O6H4)(4)(OH)(3)]center dot 4H(2)O, (NH4)(3)[CoCr2(C6O7H10)(4)(C6O7H9)]center dot 5H(2)O were characterized by elemental chemical analysis, infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy, and thermal analysis. The final oxides were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), UV-vis, IR, Raman spectroscopy (RS), magnetic measurements, N-2 adsorption-desorption analyses and X-ray photoelectron spectroscopy (XPS). XRD confirmed the cubic CoCr2O4 phase only and determined average crystallite sizes between 14 and 21 nm. Electron microscopy revealed morphology corresponding to the complete crystallization into cubic CoCr2O4. All the samples presented ferrimagnetic ordering below the Currie temperature (T-c), and a phase transition at T-s similar to 26 K attributed to the onset of long-range spiral magnetic order. The CoCr2O4 nanoparticles generated through the gluconate route following calcination at 700 degrees C for 1 h were found to have the best catalytic activity in the total oxidation of methane. (C) 2014 Elsevier Ltd. All rights reserved.

76. Physicochemical Characterization and In Vitro Cytotoxic Effect of 3-Hydroxyflavone in a Silver Nanoparticles Complex

Authors: Voicescu, M; Craciunescu, O; Moldovan, L; Anastasescu, M; Angelescu, DG; Teodorescu, VS

Published: SEP 2015, JOURNAL OF FLUORESCENCE, 25, 1223, DOI: 10.1007/s10895-015-1608-z

The aim of this work was to characterize the physico-chemical properties of 3-hydroxyflavone (3-HF) in a silver nanoparticles complex (SNPs) using UV-vis and Fluorescence spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis. One also evaluated its effect on the cell viability and morphology of L929 mouse fibroblast cells in vitro. The contribution of the carrier protein, Bovine Serum Albumin (BSA) to 3-HF properties has also been investigated. 3-HF in BSA/SNPs systems presented no cytotoxic effect in L929 mouse fibroblast cells at any of the tested concentrations. The results are discussed with relevance to the oxidative stress process.

77. Advanced ceramics in the SnO2-ZnO binary system

Authors: Mihaiu, S; Toader, A; Atkinson, I; Mocioiu, OC; Hornoiu, C; Teodorescu, VS; Zaharescu, M

Published: APR 2015, CERAMICS INTERNATIONAL, 41, 4945, DOI: 10.1016/j.ceramint.2014.12.056

In the present work, we report a systematic study of the phase formation and sintering ability of different oxide compositions in the SnO2-ZnO binary system using solid state reactions. For some selected compositions mechanically activated powders were also investigated. Structural and morphological characterizations of the samples were performed by X-ray diffraction (XRD), FT-IR Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Only the formation of Zn2SnO4 binary compound was revealed in the experimental conditions. Based on the structural results the subsolidus equilibrium phase diagram was established. The sintering ability of the studied samples was also determined, establishing the compositions domains of obtaining dense or porous ceramics. The investigation by impedance spectroscopy in the 300-600 K temperature range shows that all studied samples exhibit n-type semiconductor behavior with low values of the activation energy (0.18-0.34 eV). (C) 2014 Elsevier Ltd and Teclma Group S.r.l. All rights reserved.

78. Transition in conduction mechanism in GeSi nanostructures

Authors: Palade, C; Lepadatu, AM; Stavarache, I; Teodorescu, VS; Ciurea, ML

Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 58, DOI:

GeSi-based nanostructures show unique properties which make them suitable for integrated circuit technology. The strong interest is to enhance their electronic properties in order to improve the device performance. In order to obtain fundamental knowledge on the electrical transport taking place in GeSi nanostructures we have investigated the effects of different microstructures on the electrical behavior of GeSi nanostructured films, by modifying the annealing conditions. We manufactured GeSi nanostructured films with equiatomic composition and different structures by co-sputtering followed by adequate annealing under different temperatures. For determining the electrical behavior we performed and modeled current-temperature I - T characteristics taking into account the films structures. We found that the electrical behavior changes with the film structure by evidencing a transition in conduction mechanism. In films that are almost crystallized, being formed of small GeSi nanocrystals separated by thin amorphous regions, the I - T dependence at low temperature is due to thermally activated tunneling of carriers between neighboring nanocrystals. In contrast, in the completely crystallized films with big GeSi nanocrystals and crystallized borders between them, the electrical behavior is a typical polycrystalline one. Our findings help to clarify the conduction mechanisms taking place in GeSi nanostructures and to provide a route to electronic devices with high performance based on these materials.

79. Tuned Sensitivity Towards H2S and NH3 with Cu Doped Barium Strontium Titanate Materials

Authors: Simion, CE; Sackmann, A; Teodorescu, VS; Rusti, CF; Piticescu, RM; Stanoiu, A

Published: 2014, ELECTROCERAMICS XIV CONFERENCE, 1627, 97, DOI: 10.1063/1.4901664

The different amount of Cu-doped Barium Strontium Titanate (BST) thick film materials have been tested for their gas-sensing performances towards NH3 and H2S under dry and 50% relative humidity (RH) background conditions. The optimum NH3 sensitivity was attained with 0.1mol% Cu-doped BST whereas the selective detection of H2S was highlighted using 5mol% Cu-doped BST material. No cross-sensitivity effects to CO, NO2, CH4 and SO2 were observed for all tested materials operated at their optimum temperature (200 degrees C) under humid conditions (50% RH). The presence of humidity clearly enhances the gas sensitivity to NH3 and H2S detection.

80. Annealing induced changes in the structure, optical and electrical properties of GeTiO2 nanostructured films

Authors: Stavarache, I; Lepadatu, AM; Teodorescu, VS; Galca, AC; Ciurea, ML

Published: AUG 1 2014, APPLIED SURFACE SCIENCE, 309, 174, DOI: 10.1016/j.apsusc.2014.04.212

The GeTiO2 amorphous films were deposited by magnetron sputtering and subsequently annealed at 400, 550, 600 and 700 degrees C for nanostructuring. The structure of annealed films was investigated by X-ray diffraction and transmission electron microscopy. The transmittance spectra of all annealed GeTiO2 films were measured and simulated by using Bruggeman effective medium approximation considering components of TiO2 anatase, crystalline Ge, GeO2 and voids determined from the structure investigations. The electrical behavior of 400, 600 and 700 degrees C annealed films was studied by measuring current-voltage characteristics. We found that by increasing the annealing temperature the films thickness decreases from 330 nm (as-deposited films) to 290 nm (700 degrees C annealed films). The 400 degrees C annealed films are amorphous, while all the others annealed at higher temperatures are crystallized (X-ray diffraction and transmission electron microscopy). In the 550 and 600 degrees C annealed films we found the (TiGe)O-2 rutile structure which is formed by starting from the GeO2 tetragonal structure with high Ti content. Additionally, these films contain TiO2 anatase structure and cubic Ge nanocrystals. At 700 degrees C annealing temperature, a surface layer of GeO2 tetragonal nanocrystals is formed by Ge diffusion and a part of Ge is lost. The experimental transmittance spectra indicate a broadening of the transparency range by increasing the annealing temperature, and the simulated ones also indicate this behavior with the decrease of Ge content, the experimental and simulated spectra being in good agreement. Also, the increase of annealing temperature produces an increase of electrical conductivity. (C) 2014 Elsevier B.V. All rights reserved.

81. GeSiO Based Nanostructures: Electrical Behaviour Related to Morphology and Preparation Method

Authors: Ciurea, ML; Teodorescu, VS; Stavarache, I; Lepadatu, AM

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 73, DOI: 10.1007/978-3-662-44479-5_3

The structure of GeSiO films resulted from deposition and annealing conditions draws their electrical behaviour. GeSiO films prepared either by magnetron sputtering or sol-gel method and subsequently annealed are formed of Ge nanocrystals and/or amorphous Ge nanoparticles embedded in amorphous SiO2 matrix. Firstly, the size effect which is the main effect in these systems produces specific quantum confinement energy levels in the enlarged forbidden energy band gap in nanocrystals. Secondly, these films are percolative systems, so that the main conduction mechanisms which govern the electrical behaviour are the tunnelling and hopping between neighbouring Ge nanocrystals or amorphous nanoparticles. Accordingly, the charge transport is strongly determined by the structure and morphology of films.

82. Electrical properties related to the structure of GeSi nanostructured films

Authors: Ciurea, ML; Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS

Published: JUL 2014, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251, 1346, DOI: 10.1002/pssb.201350112

GeSi nanostructured films were obtained by cosputtering from two Ge and Si targets and subsequent annealing in furnace in N-2 for 5 h at 700, 800 and 900 degrees C, with the aim to show the correlation between electrical properties and crystalline structure of the films. The as-deposited films are amorphous, have a Ge: Si composition of 55: 45 and 185 nm thickness. The film structure was investigated by XRD and TEM, and the electrical behaviour was studied by measuring current-voltage (I-V) and current-temperature (I-T) characteristics and by discussing them in correlation with the structure. Different electrical behaviours of GeSi films corresponding to different structures have been evidenced. The 700 degrees C annealed GeSi films are formed of nanocrystals (7-15 nm) separated by amorphous regions (1-2 nm). These films present a superlinear I-V characteristic typical of high field-assisted tunnelling through potential barriers (amorphous regions) between nanocrystals. The I-T characteristic at low temperature follows a T-1/2 law showing a thermally activated tunnelling of carriers between neighboring GeSi nanocrystals. The films annealed at 800 and 900 degrees C have a like behavior, they are completely crystallized and present linear I-V and Arrhenius I-T dependences reflecting the polycrystalline behaviour. [GRAPHICS] . (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

83. Indium-tin nanoscaled oxides synthesized under hydrothermal supercritical and postannealing pathway: Phase dynamics and characterization

Authors: Diamandescu, L; Tarabasanu-Mihaila, D; Feder, M; Enculescu, M; Teodorescu, VS; Constantinescu, S; Popescu, T; Bartha, C; Pap, Z

Published: FEB 14 2014, MATERIALS CHEMISTRY AND PHYSICS, 143, 1549, DOI: 10.1016/j.matchemphys.2013.11.064

With the aim of synthesizing the mixed nanoparticle system xIn(2)O(3)-(1-x)SnO2 over all molar concentration range 0 <= x <= 1, Delta x = 0.1, we performed hydrothermal supercritical experiments on indium-tin hydrogel resulted from InCl3-SnCl4 water solution. Nanophases isostructural with InOOH and SnO2 were obtained by hydrothermal reaction at 400 degrees C, in the molar concentration range of 0.1 <= x <= 0.7; at x = 0.8 and x = 0.9 only one phase, isostructural with InOOH, was observed. Samples calcined at 500 degrees C with x in the range of 0.2 <= x <= 0.7 contain a nanoscaled phase isostructural with rhombohedral In2O3 and a second one isostructural with tetrahedral SnO2. At x = 0.8 and x = 0.9 only one phase isostructural with rhombohedral In2O3 appears: rhombohedral ITO phase. The determined band gap energies could recommend the rhombohedral ITO structure for visible light photocatalytic applications. The phase dynamics together with the concentration range for existence of the solid solutions in the InOOH-SnO2 and In2O3-SnO2 composite semiconducting nanoparticle systems have been evidenced and discussed. (C) 2013 Elsevier B.V. All rights reserved.

84. Charge storage properties of HfO2/Ge-HfO2/SiO2 trilayer structures

Authors: Palade, C; Slav, A; Lepadatu, AM; Teodorescu, VS; Ciurea, ML

Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 62, DOI:

We report on the charge storage properties of trilayer structures consisting in sputtered gate HfO2/co-sputtered Ge-HfO2 layer/rapid thermal tunneling SiO2 oxide. Investigations of transmission electron microscopy and X-ray diffraction evidence the formation of HfO2 with mixed structure of monoclinic and tetragonal in the annealed structures. Capacitance-voltage (C-V) characteristics were measured on Al/HfO2/Ge-HfO2/SiO2/Si/Al metal-oxide-semiconductor capacitors based on as-deposited and annealed structures. Large C-V hysteresis is observed for the as-deposited structures and is controlled by traps present in oxide and interface. The annealing yields a C-V hysteresis with smaller memory window being due to injected charges in Ge nanocrystals.

85. Biological evaluation of 3-hydroxyflavone in a silver nanoparticles complex

Authors: Voicescu, M; Ionescu, S; Anastasescu, M; Craciunescu, O; Tatia, R; Moldovan, L; Angelescu, DG; Teodorescu, VS

Published: SEP 2014, FEBS JOURNAL, 281, 402, DOI:

86. Si/SiO2 quantum dots cause cytotoxicity in lung cells through redox homeostasis imbalance

Authors: Stan, MS; Memet, I; Sima, C; Popescu, T; Teodorescu, VS; Hermenean, A; Dinischiotu, A

Published: SEP 5 2014, CHEMICO-BIOLOGICAL INTERACTIONS, 220, 115, DOI: 10.1016/j.cbi.2014.06.020

Si/SiO2 quantum dots (QDs) are novel particles with unique physicochemical properties that promote them as potential candidates for biomedical applications. Although their interaction with human cells has been poorly investigated, oxidative stress appears to be the main factor involved in the cytotoxicity of these nanoparticles. In this study, we show for the first time the influence of Si/SiO2 QDs on cellular redox homeostasis and glutathione distribution in human lung fibroblasts. The nanoparticles morphology, composition and structure have been investigated using high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. MRC-5 cells (human lung fibroblasts) were incubated with various concentrations of Si/SiO2 QDs ranging between 25 and 200 mu g/mL for up to 72 h. The results of the MTT and sulforhodamine B assays showed that exposure to QDs led to a time-dependent decrease in cell viability and biomass. The increase in reactive oxygen species (ROS) and malondialdehyde (MDA) levels together with the lower glutathione content suggested that the cellular redox homeostasis was altered. Regarding GSH distribution, the first two days of treatment resulted in a localization of GSH mainly in the cytoplasm, while at longer incubation time the nuclear/cytoplasmic ratio indicated a nuclear localization. These modifications of cell redox state also affected the redox status of proteins, which was demonstrated by the accumulation of oxidized proteins and actin S-glutathionylation. In addition, the externalization of phosphatidylserine provided evidence that apoptosis might be responsible for cell death, but necrosis was also revealed. Our results suggest that Si/SiO2 quantum dots exerted cytotoxicity on MRC-5 cells by disturbing cellular homeostasis which had an effect upon protein redox status. (C) 2014 Elsevier Ireland Ltd. All rights reserved.

87. In vitro toxicity evaluation of Ti4+-stabilized gamma-Bi2O3 sillenites

Authors: Popescu, T; Lupu, AR; Feder, M; Tarabasanu-Mihaila, D; Teodorescu, VS; Vlaicu, AM; Diamandescu, L

Published: DEC 2014, TOXICOLOGY IN VITRO, 28, 1530, DOI: 10.1016/j.tiv.2014.07.003

We report results regarding the in vitro toxicology of gamma-Bi2O3 represented by its isomorphous phase Bi12TiO20 (gamma-BTO). The gamma-BTO microparticles were synthesized by two methods: coprecipitation from a bismuth nitrate tetrabutyl titanate solution and solid state reaction of Bi2O3 and TiO2 oxides. The structural and morphological characteristics of the obtained materials were determined using X-ray diffraction (XRD), selected area electron diffraction (SAED), transmission (TEM) and scanning (SEM) electron microscopy. The elemental composition was investigated using energy dispersive spectrometry (EDS). The cytotoxicity and oxidative/nitrosative stress (intracellular reactive oxygen species (ROS) and nitric oxide (NO) release) induced by the studied microparticles in HepG2, SH-SY5Y and 3T3-L1 cell cultures were determined using the MIT, DCF-DA (2 ',7 '-dichlorfluorescein-diacetate) and Griess methods respectively. Depending on the cell type and gamma-BTO concentration, results showed only weak cytotoxic effects after 24 h of gamma-BTO exposure and cell proliferation effects for longer treatment times. Only reduced NO release increases (corresponding to high gamma-BTO concentrations) were detected in case of SH-SY5Y and 3T3-L1 cells. The intracellular ROS production (higher for HepG2 cells) appeared inversely proportional to the gamma-BTO concentration. The obtained results indicated a promising in vitro biocompatibility of gamma-BTO and encourage further studies regarding its potential for biomedical applications. (C) 2014 Elsevier Ltd. All rights reserved.

88. Substrate impact on optical and microstructural properties of TiO2-PEG sol-gel films

Authors: Anastasescu, M; Teodorescu, VS; Buiu, O; Osiceanu, P; Calderon-Moreno, JM; Predoana, L; Preda, S; Nicolescu, M; Marin, A; Serban, B; Mihaila, M; Stoica, M; Zaharescu, M; Gartner, M

Published: SEP 2014, CERAMICS INTERNATIONAL, 40, 11811, DOI: 10.1016/j.ceramint.2014.04.012

Nanosized TiO2 layers containing polyethylene glycol (PEG) with 20,000 molecular weight were prepared by sol gel method and deposited on three different substrates: microscope standard slides, Fluorine doped Tin Oxide (FTO) glass and Silicon, followed by thermal treatment at 450 degrees C. The effects of the substrate on the microstructural, morphological, chemical and optical properties of the films have been studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), X-ray Photo-electron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE). The XRD showed that the film crystallization depends very much on the substrate used, thus the films deposited on glass are amorphous even after 1 h thermal treatment at 450 degrees C, while the films deposited on Silicon and FTO substrates are crystallized in anatase phase, in good agreement with the TEM analysis. The XPS analysis showed that a rather high carbon relative concentration in the TiO2 film (without PEG) exists; this suggests that an unavoidable carbon contamination occurs and is not related on the presence or absence of PEG. The thickness and surface roughness of the films are clearly dependent on the substrate type. The flat surfaces of glass and Si lead to the formation of thinner TiO2 films (around 30 nm thicknesses), while the FTO substrate surface leads to thicker film (thickness similar to 100 nm). The porosity of TiO2 films as found by SEM and TEM analyzes is dependent of substrate type; small pore sizes up to 20 nm are characteristic for the films deposited on glass, while larger pore sizes up to 200 nm are found for the films deposited on FTO substrate. Not least, the film transmissions in the visible region are also substrate dependent and the highest values (80%) were obtained for the films deposited on glass. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

89. Influence of the TiO2 precursors on the thermal and structural stability of titanate-based nanotubes

Authors: Preda, S; Teodorescu, VS; Musuc, AM; Andronescu, C; Zaharescu, M

Published: FEB 2013, JOURNAL OF MATERIALS RESEARCH, 28, 303, DOI: 10.1557/jmr.2012.362

The influence of different TiO2 precursors (laboratory-prepared sol-gel powders, dried and thermally treated at 400 degrees C, and commercial powders such as anatase by Aldrich and P25 Aeroxide by Evonik) on the structure and morphology of the titanate nanotubes obtained by hydrothermal method was investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. In all cases, titanate-based nanotubes were obtained, having similar structure and morphology. The effect of the thermal treatment on the structural stability was also studied by differential thermal analysis and thermogravimetry analysis (TG/DTA) and differetial scanning calorimetry (DSC) measurements up to 600 degrees C, to determine the transformation of titanate nanotubes into other phases. Complementarily, by XRD investigation, the phases that develop after the thermal treatment of the titanate nanotubes in 110-400 degrees C temperature range were identified. The TEM micrographs come to confirm the deterioration of morphology and transformation from nanotubes to particles. The thermal stability of the investigated nanotubes led to the conclusion that this property depends not only on the sodium content but also on the type of precursor. The highest thermal stability was noticed for the nanotubes synthesized starting with anatase (Aldrich) commercial powder.

90. Structure and dielectric properties of low fluence excimer laser annealing of sol-gel HfO2 thin films deposited on Si wafer

Authors: Teodorescu, VS; Maraloiu, AV; Blanchin, MG; Yamada, T; Sandu, CS; Delaporte, P; Zaharescu, M

Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 80, DOI:

Sol-gel HfO2 thin films, prepared from etoxid precursor, were deposited onto silicon wafer substrates by dipcoating. Low fluence multipulse excimer laser processing was used for sol-gel film densification. The small duration of the laser pulse heating limits the quantity of oxygen atoms arriving from the surface at the HfO2/Si interface. Laser irradiations were performed using a XeCl (308 nm) excimer laser, with a homogeneous laser beam. The nanostructure evolution of the laser irradiated films, using different laser fluences between 30 and 120 mJ/cm(2) and different number of pulses, was studied by systematic cross section transmission electron microscope (XTEM) observations. Dielectric constant measurements were performed on the sol-gel HfO2 films samples after laser annealing. The optimum laser processing conditions were found to be a laser fluence of 80 mJ/cm(2) and 5000 to 10000 laser pulses. In these conditions, uniform densified HfO2 amorphous films with a dielectric constant of about 25 were obtained.

91. Formation mechanism of CdS nanoparticles with tunable luminescence via a non-ionic microemulsion route

Authors: Angelescu, DG; Munteanu, G; Anghel, DF; Peretz, S; Maraloiu, AV; Teodorescu, VS

Published: JAN 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-012-1376-5

We investigated the synthesis of CdS nanoparticles via an optimized water-in-oil microemulsion route that used the non-ionic surfactantbased system H2O-n-octane-Brij30/1-octanol. For that purpose, a microemulsion that contained Cd(II) ions (mu e1) and another microemulsion that contained S2- ions (mu e2) were combined. To investigate the ways in which the non-ionic microemulsion characteristics controlled the size and emission properties of colloidal CdS quantum dots, mu e1 and mu e2 with tunable and robust similar structure were prepared. This requirement was fulfilled by matching the water emulsification failure boundary (wefb) of the two microemulsions and carrying out synthesis along this boundary. Dynamic light scattering and fluorescence probe techniques were used to investigate the size and interfacial organization of the microemulsion water droplets, and the CdS nanoparticles were characterized by UV-Vis and static fluorescence spectrometry, TEM and HRTEM. Nanoparticles of diameter 4.5-5.5 nm exhibiting enhanced band edge emission were produced by increasing the water content of the precursor microemulsions. The experimental results were combined with a Monte Carlo simulation approach to demonstrate that growth via coagulation of seed nuclei represented the driving mechanism for the CdS nanoparticle formation in the water-in-oil microemulsion.

92. SOL-GEL HYBRID NANOCOMPOSITES WITH OXIDE NANOPARTICLES

Authors: Predoana, L; Gartner, M; Teodorescu, VS; Nicolescu, M; Anastasescu, M; Zaharescu, M

Published: FEB-MAR 2013, REVUE ROUMAINE DE CHIMIE, 58, 249, DOI:

In the present work the influence of the method of preparation on the characteristics of sol-gel hybrid nanocomposites with oxide nanoparticles was studied. The chosen system consists of a SiO2 matrix based on methyltriethoxysilane (MTEOS) and laboratory made TiO2:CeO2 (4:1) nanopowder. The doping of the matrix was realized either by dispersion of previously prepared binary nanopowder in the matrix solution or by in situ generation of the TiO2-CeO2 nanoparticles during the matrix hydrolysis-condensation processes. Films were deposited on silicon wafer and glass substrates by dip-coating method and were characterized as prepared and annealed at 120 degrees C. The optical and morphological properties were determined by spectroellipsometry (SE), scanning electron microscopy (SEM), atomic force microscopy (AFM), their structural characterization was realized by IR spectroscopy and the thermal behavior was determined by thermogravimetric and differential-thermal analysis (TG/DTA). All characterization methods have shown that by the two preparation routes materials with different characteristics were obtained.

93. TRANSMISSION ELECTRON MICROSCOPY STUDY OF Ge NANOPARTICLES FORMED IN GeSiO FILMS BY ANNEALING IN HYDROGEN

Authors: Teodorescu, VS; Maraloiu, AV; Stavarache, I; Lepadatu, AM; Ciurea, ML

Published: OCT-DEC 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1780, DOI:

This paper presents a detailed transmission electron microscopy (TEM) study of GeSiO films with Ge nanoparticles. The films with 2.5 mu m thickness were deposited by magnetron sputtering and subsequently annealed in H-2 at 2 atm and 500 degrees C for 2 h for nanostructuring. After H-2 annealing, the majority of the resulted Ge nanoparticles are amorphous, less than 5 nm in size, forming a uniform network in the film volume. Big Ge nanoparticles with sizes between 20 and 50 nm are also formed. Some of them are identified to be crystallized in the (Ge-III/ST12) tetragonal phase. The high resolution TEM observation induces the amorphysation of the Ge tetragonal phase, followed by the crystallization of the amorphous Ge phase in the cubic diamond structure (Ge-I), as an effect of electron irradiation. A secondary annealing performed in N-2 at 800 degrees C and 1 atm for 2 h induces formation of faceted cubic Ge nanoparticles distributed in the SiO2 matrix.

94. Detailed characterization of functionalized magnetite and ascertained effects

Authors: Culita, DC; Patron, L; Oprea, O; Bartha, C; Palade, P; Teodorescu, V; Filoti, G

Published: SEP 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1916-7

The paper reports on magnetite successfully functionalized with two new molecules. The investigations, involving chemical and physical methods, provided relevant features involving cell parameters and grain sizes, or the intermingling ratio between magnetite and functionalizing molecules, as deduced from magnetic measurements. A large amount of interesting data concerning various surface and local interaction mechanisms was supplied by detailed Mossbauer measurements. The new outputs are explained in terms of material processing and intimate mixing of the involved molecules.

95. Spectroscopic analysis of the riboflavin-serum albumins interaction on silver nanoparticles

Authors: Voicescu, M; Angelescu, DG; Ionescu, S; Teodorescu, VS

Published: APR 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1555-z

Spectrophotometric behavior of riboflavin (RF) adsorbed on silver nanoparticles as well as its interaction with two serum albumins, BSA and HSA, respectively, has been evidenced. The time evolution of the plasmonic features of the complexes formed by RF/BSA/HSA and Ag(0) nanoparticles having an average diameter of 10.0 +/- 2.0 nm have been investigated by UV-Vis absorption spectroscopy. Using steady-state and time-resolved fluorescence spectroscopy, the structure, stability, and dynamics of the serum albumins have been studied. The efficiency of energy transfer process between RF and serum albumins on silver nanoparticles has been estimated. A reaction mechanism of RF with silver nanoparticles is also proposed and the results are discussed with relevance to the involvement of the silver nanoparticles to the redox process of RF and to the RF-serum albumins interaction into a silver nanoparticles complex.

96. Conduction mechanism versus annealing in SiO2 films with Ge nanoparticles

Authors: Palade, C; Lepadatu, AM; Stavarache, I; Teodorescu, VS; Ciurea, ML

Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 34, DOI:

This paper analyses and discusses the effect of Ge/Si atomic ratio and annealing temperature on the conduction mechanisms governing the electrical behavior of Ge-SiO2 films containing Ge nanoparticles embedded in amorphous SiO2 matrix. For this, the experimental conductance-temperature curves are modeled in correlation with the microstructure findings for two types of films. One type of films has a lower Ge/Si ratio of 0.73 and was obtained by magnetron sputtering followed by annealing in H-2, at 500 degrees C, while the second one has a higher ratio of 1.86 and was obtained also by sputtering, but was annealed in N-2, at 800 degrees C. Both types of films show an electrical behavior with a T-1/4 conductance dependence on temperature, typical for hopping mechanism.

97. Dense Ge nanocrystal layers embedded in oxide obtained by controlling the diffusion-crystallization process

Authors: Lepadatu, AM; Stoica, T; Stavarache, I; Teodorescu, VS; Buca, D; Ciurea, ML

Published: SEP 15 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1981-y

Amorphous Ge/SiO2 multilayer structures deposited by magnetron sputtering have been annealed at different temperatures between 650 and 800 degrees C for obtaining Ge nanocrystals in oxide matrix. The properties of the annealed structures were investigated by transmission electron microscopy, Raman spectroscopy, and low temperature photoluminescence. The Ge crystallization is partially achieved at 650 degrees C and increases with annealing temperature. Insight of the Ge nanocrystal formation was acquired by comparing two annealing procedures, i.e., in a conventional tube furnace and by a rapid thermal annealing. By rapid thermal annealing in comparison to conventional furnace one, the Ge crystallization process is faster than Ge diffusion, resulting in the formation of more compact layers of Ge nanocrystals with 8-9.5-nm size as Raman spectroscopy reveals. These findings are important to improve the annealing efficiency in the nanocrystals formation for a precise control of their sizes and location in oxide matrix and for the possibility to create systems with interacting nanoparticles for charge or excitonic transfer. The infrared photoluminescence of Ge nanocrystals at low temperatures shows strong emission with two sharp peaks at about 1,000 meV.

98. Increased Diffusion Coefficient of Polymeric Nanocomposite Layer for Gas Sensing Applications

Authors: Nicolae, I; Viespe, C; Serban, N; Negrila, CC; Teodorescu, VS; Trupina, L

Published: DEC 2013, SENSOR LETTERS, 11, 2332, DOI: 10.1166/sl.2013.3083

A high-performance polymeric nanostructured sensing layer for a surface acoustic wave sensor, deposited using a modified matrix assisted pulsed laser evaporation direct write technique, exhibited improved performance in terms of response time and frequency deviation. In the present work, we assessed the factors and mechanisms that account for the layer's increased sensing capabilities. The increase in the sensing performance was attributed to an increased diffusion constant, due to greater molecular mobility of polymeric chains caused by the nanoparticles embedded in the polymer matrix.

99. Effects of TiO2 nanoparticles on the NO2- levels in cell culture media analysed by Griess colorimetric methods

Authors: Popescu, T; Lupu, AR; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS; Raditoiu, V; Purcar, V; Vlaicu, AM

Published: FEB 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1449-0

The Griess assay has been used to determine the possible changes in the measured NO2- concentrations induced by TiO2 nanoparticles in three types of nitrite-containing samples: aqueous NaNO2 solutions with known concentrations, and two types of cell culture media-Roswell Park Memorial Institute medium (RPMI-1640) and Dulbecco's Modified Eagle Medium (DMEM-F12) used either as delivered or enriched in NO2- by NaNO2 addition. We have used three types of titania with average particle sizes between 10 and 30 nm: Degussa P25 and two other samples (undoped and Fe3+-doped anatase TiO2) synthesised by a hydrothermal route in our laboratory. The structural, morphological, optical and physicochemical characteristics of the used materials have been studied by X-ray diffraction, transmission electron microscopy (EDX), Mossbauer spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption, UV-Vis reflectance spectroscopy, dynamic light scattering and diffuse reflectance infrared Fourier transform spectroscopy. The opacity and sedimentation behaviour of the studied TiO2 suspensions have been investigated by photometric attenuance measurements at 540 nm. To account for the photocatalytic properties of titania in a biologically relevant context, multiple Griess tests have been performed under controlled exposure to laboratory natural daylight illumination. The results show significant variations of light attenuance (associated with NO2- concentrations in the Griess test) depending on the opacity, sedimentation behaviour, NO2- adsorption and photocatalytic properties of the tested TiO2 nanomaterials. These findings identify material characteristics recommended to be considered when analysing the results of Griess tests performed in biological studies involving TiO2 nanoparticles.

100. Synthesis and association of Ag(0) nanoparticles in aqueous Pluronic F127 triblock copolymer solutions

Authors: Angelescu, DG; Vasilescu, M; Anastasescu, M; Baratoiu, R; Donescu, D; Teodorescu, VS

Published: JAN 20 2012, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 394, 66, DOI: 10.1016/j.colsurfa.2011.11.025

Triblock copolymers poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) Pluronic F127 was employed as capping agent for the Ag(0) metallic nanoparticles synthesized by the chemical reduction of silver nitrate, AgNO3, with excess of sodium borohydride, NaBH4. The morphology and the kinetics of Ag(0) nanoparticles were studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), UV-vis absorption and fluorescence probe technique. Spherical polydisperse particles of 12 +/- 4 nm mean diameter at varying the Pluronic concentration in the range of 0.13-13 wt.% were reported. Apart from the stabilizing role, the triblock copolymer promoted the agglomeration of individual Ag(0) nanoparticles in small assemblies whose plasmon band features differed from those of the individual nanoparticles. The formation of Ag(0) nanoparticles-F127 complex took place after full reduction of the Ag ions and it was controlled by the F127 concentration. The nanoparticle morphology and the fluorescence probe technique suggested that the excess PI uronic drove indirectly the Ag(0) nanoparticles association. Free F127 polymeric micelles encountered above critical micellar concentration (cmc) promoted the partial desorption of the adsorbed triblock copolymer and subsequently weakened the stability of the individual nanoparticles. (C) 2011 Elsevier B.V. All rights reserved.

101. Structure and electrical transport in films of Ge nanoparticles embedded in SiO2 matrix

Authors: Stavarache, I; Lepadatu, AM; Maraloiu, AV; Teodorescu, VS; Ciurea, ML

Published: JUL 2012, JOURNAL OF NANOPARTICLE RESEARCH, 14, DOI: 10.1007/s11051-012-0930-5

The films containing Ge nanoparticles embedded in SiO2 matrix were prepared by RF magnetron sputtering and subsequently by thermal annealing. Their structure was investigated by conventional transmission electron microscopy and high resolution transmission electron microscopy together with energy-dispersive X-ray spectroscopy. The electrical behavior of films was studied by measuring current-temperature and current-voltage characteristics. The structure investigation reveals two kinds of features: a low density of big Ge nanoparticles with sizes from 20 to 50 nm and a network of small amorphous Ge nanoregions/nanoparticles (5 nm size or less) with high density, both being embedded in amorphous SiO2 matrix. The electrical transport was shown to take place through the network of amorphous Ge nanoregions. At low temperature, the T-1/4 dependence of the current was evidenced, while at high temperature, the T-1 Arrhenius dependence was found. At both low and high temperatures, the conductivity is nearly constant. The behavior at low temperature was explained by the hopping mechanism on localized states located in a band near the Fermi energy, while at high temperature by the charge excitation to the extended states.

102. TRANSPORT MECHANISMS IN SiO2 FILMS WITH EMBEDDED GERMANIUM NANOPARTICLES

Authors: Palade, C; Lepadatu, AM; Stavarache, I; Maraloiu, AV; Teodorescu, VS; Ciurea, ML

Published: 2012, 2012 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 2, 94, DOI:

This paper reports on the conduction mechanisms in amorphous SiO2 films with embedded Ge nanoparticles. For this, measurements of current-temperature and current-voltage were employed and correlated with the microstructure results obtained from transmission electron microscopy (TEM). TEM images reveal that our films contain big Ge nanoparticles with low density and small Ge nanoparticles with high density, the last ones being the only responsible for the electrical transport. Two transport mechanisms were found at low and high temperature respectively, namely hopping on localized states in a band near Fermi level and charge excitation to the extended states at mobility edge.

103. Influence of the substrate and nitrogen amount on the microstructural and optical properties of thin r.f.-sputtered ZnO films treated by rapid thermal annealing

Authors: Nicolescu, M; Anastasescu, M; Preda, S; Stroescu, H; Stoica, M; Teodorescu, VS; Aperathitis, E; Kampylafka, V; Modreanu, M; Zaharescu, M; Gartner, M

Published: NOV 15 2012, APPLIED SURFACE SCIENCE, 261, 823, DOI: 10.1016/j.apsusc.2012.08.104

N-doped ZnO (ZnO: N) thin films, intended to be used as one of the layers in solar cell applications were deposited by r.f. sputtering, using ZnN target (99.9% purity), on silicon and fused silica substrates. In the gas flow composition, Ar was kept constant (50%) and the O-2/N-2 ratio was varied as: 40%/10%, 25%/25% and 10%/40%. After deposition, rapid thermal annealing (RTA) at 400 and 550 degrees C for 1 min in N-2 ambient has been performed. The RTA impact on the optical and microstructural properties of ZnO: N thin films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX), UV-vis-NIR spectroscopy, UV-vis-NIR spectroscopic ellipsometry (SE) and infrared ellipsometry (IR-SE). The as-deposited (ad) ZnO: N films are polycrystalline with preferentially oriented columnar crystals. After RTA we found ZnO: N films with improved crystallinity and fewer boundary defects. We report optical constants of ZnO: N from UV to IR spectral range as well as the infrared active phononic modes. (C) 2012 Elsevier B. V. All rights reserved.

104. ELECTRICAL BEHAVIOUR RELATED TO STRUCTURE OF NANOSTRUCTURED GeSi FILMS ANNEALED AT 700 degrees C

Authors: Lepadatu, AM; Stavarache, I; Maraloiu, A; Palade, C; Teodorescu, VS; Ciurea, ML

Published: 2012, 2012 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 2, 112, DOI:

In this paper we continue the previous investigations on nanostructured GexSi1-x films. The films were deposited by magnetron sputtering and annealed in N-2 atmosphere at 700 degrees C. Their structure was investigated and correlated with the electrical behavior. For this, conventional and high-resolution transmission electron microscopy together with selected area electron diffraction was used. Electrical measurements of current-voltage and current-temperature curves were made. The majority of crystallites that forms the films have the composition Ge50Si50 and 15 - 30 nm size. The I - T characteristics have Arrhenius dependence, with two activation energies interpreted as transitions between quantum confinement levels.

105. Structural investigations of Ge nanoparticles embedded in an amorphous SiO2 matrix

Authors: Stavarache, I; Lepadatu, AM; Gheorghe, NG; Costescu, RM; Stan, GE; Marcov, D; Slav, A; Iordache, G; Stoica, TF; Iancu, V; Teodorescu, VS; Teodorescu, CM; Ciurea, ML

Published: JAN 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 232, DOI: 10.1007/s11051-010-0021-4

Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO2 matrix. GeSiO thin films are prepared by two methods, sol-gel and radio frequency magnetron sputtering. After the deposition, the sol-gel films are annealed in either N-2 (at 1 atm and 800 A degrees C) or H-2 (at 2 atm and 500 A degrees C), and the sputtered films in H-2 (at 2 atm and 500 A degrees C), to allow Ge segregation. Amorphous Ge-rich nanoparticles (3-7 nm size) are observed in sol-gel films. Crystalline Ge nanoparticles in the high pressure tetragonal phase (10-50 nm size) are identified in the sputtered films. The size of the nanoparticles increases with Ge concentration in the volume of the film. At the film surface, the Ge concentration is much larger that in the volume for both sol-gel and sputtered films. At the same time, at the film surface, only oxidized Ge is observed.

106. PREPARATION AND ELECTRICAL CHARACTERIZATION OF SiGe NANOSTRUCTURES

Authors: Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS; Ciurea, ML

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 52, DOI:

This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temperature characteristics were taken. Nanostructures have different electrical behavior. Current-voltage curves are linear, while current-temperature curves are dependent on the annealing temperature. In films annealed at 650 degrees C, electrical transport is controlled by quantum confinement effect and localized states (current-temperature characteristics), while in films annealed at 900 degrees C it is controlled by tunneling of thermally activated carriers between neighboring nanocrystals.

107. CuS NANOPARTICLES OBTAINED IN PRESENCE OF ONE SURFACTANT

Authors: Simonescu, CM; Capatina, C; Teodorescu, VS; Florea, G

Published: 2011, METALURGIA INTERNATIONAL, 16, 146, DOI:

In this study, copper sulfide CuS (covellite) was obtained, starting from the Cu(CH3COO)(2)center dot H2O and thiourea ((NH2CSNH2) system, and working in presence or absence of sodium-bis(2-ohylhexyl) sulfosuccinate (Na-AOT). Samples obtained from Cu(CH3COO)(2)center dot H2O:NH2CSNH2:Na-AOT system were deposited as thin films on the glass substrates. CuS samples obtained were characterized by X ray diffraction, IR spectroscopy, TEM transmission electron microscopy and SAED - selected area electron diffraction. The influence of surfactant on the shape and size of CuS (covellite) nanocrystals was established.

108. Electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride

Authors: Stavarache, I; Lepadatu, AM; Teodorescu, VS; Ciurea, ML; Iancu, V; Dragoman, M; Konstantinidis, G; Buiculescu, R

Published: 2011, NANOSCALE RESEARCH LETTERS, 6, DOI: 10.1186/1556-276X-6-88

The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima.

109. BINARY VANADIUM-CERIUM OXIDE NANOPOWDERS OBTAINED BY SOFT CHEMISTRY

Authors: Zaharescu, M; Todan, L; Predoana, L; Atkinson, I; Rusu, A; Andronescu, C; Teodorescu, V; Osiceanu, P

Published: NOV-DEC 2010, REVUE ROUMAINE DE CHIMIE, 55, +, DOI:

Vanadium-cerium oxide gels and films obtained by the sot-gel method have been widely studied, due to their catalytic, electrochemical, electronic and ionic properties, a result of their ability to form combinations in more than one valence state. V-Ce oxide powders were synthesized by wet chemical methods, in the presence and absence of polyols. The preparation of an aqueous dispersion of mixed vanadium oxide/CeO2 started from a solution of the corresponding metal oxide and metal salt, V2O5 and Ce(NH4)(NO3)(6), respectively. The powders were characterized by IR-spectroscopy, X-ray photoelectronic spectroscopy, X-ray diffraction, electronic microscopy (TEM, SAED, HRTEM). The influence of the ratio of the components (V/Ce) and of the polyol complexation agent on the structure and morphology of the obtained binary oxide powders was established.

110. Investigation of microstructural properties of nitrogen doped ZnO thin films formed by magnetron sputtering on silicon substrate

Authors: Nicolescu, M; Anastasescu, M; Preda, S; Calderon-Moreno, JM; Osiceanu, P; Gartner, M; Teodorescu, VS; Maraloiu, AV; Kampylafka, V; Aperathitis, E; Modreanu, M

Published: MAY 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1051, DOI:

Zinc oxide (ZnO) is a semiconductor with a wurtzite-type structure, useful for a variety of optical, optoelectronic and piezoelectric applications. We report here on the post deposition treatment (Rapid Thermal Annealing at 400 and 550 degrees C) impact on the microstructural properties of N-doped ZnO (ZnO:N) thin films grown on silicon substrate by r.f. magnetron sputtering of ZnN target. The ZnO:N films have been characterized by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning (SEM) and Transmission (TEM) Electron Microscopy coupled with Energy Dispersive X-ray (EDX) and Selected Area Electron Diffraction (SAED) respectively and Fourier Transform Infrared (FTIR) Spectroscopy. XRD confirms that ZnO:N films are polycrystalline in the as deposited state. SEM, TEM and XRD measurements revealed a polycrystalline film with preferentially oriented columnar crystals. AFM studies reveal a drastic change of ZnO surface morphology upon RTA and the existence of areas with different roughness in the sample thermally treated at 400 degrees C. FTIR, XRD and TEM results shows that disorder associated mainly with grain boundary defects decreases as the annealing temperature increases.

111. Kinetics and optical properties of the silver nanoparticles in aqueous L64 block copolymer solutions

Authors: Angelescu, DG; Vasilescu, M; Somoghi, R; Donescu, D; Teodorescu, VS

Published: AUG 20 2010, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 366, 162, DOI: 10.1016/j.colsurfa.2010.06.001

Silver nanoparticles were prepared by the chemical reduction of silver nitrate, AgNO3, with excess of sodium borohydride, NaBH4, in dilute aqueous solutions containing triblock copolymers poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) Pluronic L64. The synthesis was completed in similar to 24h and produced highly stable particle dispersion. The growth of nanoparticles was assessed by combining Mie theory, UV-vis spectroscopy and dynamic light scattering, and the average particle size was determined from transmission electron microscopy. The silver nanoparticles were sterically stabilised as a result of the block copolymer adsorption onto the nanoparticle surface. Besides the stabilizing character, the copolymer affected the kinetics of particle growth, the size and optical properties of as-synthesized Ag nanoparticles. It was revealed that the particle formation took place in two distinct stages. The first step was dominated by Ag ion reduction and growth driven by accretion, while in the second stage coagulated clusters of nanoparticles were obtained obtained. The as-synthesized particles were polydisperse, the individual ones had a size of similar to 7.6 nm as given by transmission electron microscopy, and the hydrodynamic radius of clusters amounted to 60 nm. The silver nanoparticles exhibited broad and structured emission bands centered at 300 and 330 nm for excitation wavelengths in two different ranges, 220-240 nm and 260-290 nm, respectively. This process may be assigned to two emission components corresponding to two different excitation wavelength domains. (C) 2010 Elsevier B.V. All rights reserved.

112. Surface topography and optical properties of nitrogen doped ZnO thin films formed by radio frequency magnetron sputtering on fused silica substrates

Authors: Nicolescu, M; Anastasescu, M; Preda, S; Calderon-Moreno, JM; Stroescu, H; Gartner, M; Teodorescu, VS; Maraloiu, AV; Kampylafka, V; Aperathitis, E; Modreanu, M

Published: JUN 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1349, DOI:

We report here on the nitrogen doped ZnO (ZnO:N) thin films deposited by radio frequency (rf) magnetron sputtering using ZnN target (99.9% purity) on, unintentionally heated, fused silica substrates. After deposition Rapid Thermal Annealing (RTA) at 400 and 550 degrees C for 1min in N-2 ambient have been performed on the ZnO:N thin films. The RTA impact on the optical and microstructural properties of ZnO:N thin films have been investigated by X-ray diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy coupled with Energy Dispersive X-ray analysis, UV-VIS-NIR spectrophotonnetry and UV-VIS-NIR-Far IR Spectroscopic Ellipsometry. XRD and AFM results revealed an improvement in the crystalline state of ZnO:N and a reduction in the films surface roughness following RTA. The EDX spectrum showed the presence of the nitrogen in small quantities in the ZnO structure (nitrogen/oxygen=1/8). The optical constants of ZnO:N from UV down to Far IR spectral range together with the infrared active modes for ZnO:N are also reported.

113. Preparation and patterning of nanoscale hybrid materials for micro-optics

Authors: Obreja, P; Cristea, D; Teodorescu, VS; Dinescu, A; Obreja, AC; Comanescu, F; Rebigan, R

Published: OCT 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 2013, DOI:

The refractive index of organic polymers can be modified by incorporation of inorganic nanoparticles with higher or lower refractive index. The paper presents our experimental results regarding the preparation of hybrid nanocomposite films with controlled refractive index for micro-optics and integrated optics. These materials were obtained by chemical routes and sol-gel processes from commercial polymers (PMMA, PVA), metal (Ag), metal oxide nanoparticles (TiO2, ZrO2) or organic materials (Rhodamine, Alq3). The properties of these materials depend on the composition, metal/oxide concentration, particle size and dispersion homogeneity. The hybrid nanocomposite films were characterized using spectroellipsometry, UV-VIS spectroscopy, AFM, TEM and the optical properties were correlated with processing parameters. Micro/nano pattering techniques based on combination of electron beam lithography and replication techniques have been developed to obtain structures with applications in micro-optics. Components like micro-lenses, diffractive optical elements and optical waveguides have been obtained and characterized using SEM and AFM.

114. SiO2 nanospheres and tubes obtained by sol-gel method

Authors: Anastasescu, C; Anastasescu, M; Teodorescu, VS; Gartner, M; Zaharescu, M

Published: OCT 1 2010, JOURNAL OF NON-CRYSTALLINE SOLIDS, 356, 2640, DOI: 10.1016/j.jnoncrysol.2010.03.038

Multifunctional nanomaterials with one-dimensional structure have become very attractive because of their potential applications in biochemistry (bioseparation and biointeraction), drug delivery, catalysis, nanotechnology (optical sensors). In this work we report on the synthesis of SiO2 nanospheres and tubes, in a solution of tartaric acid (TTA), pure water and absolute ethanol, starting with tetraethyl orthosilicate (TEOS) via the addition of ammonium hydroxide. In order to characterize the obtained material, transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), thermogravimetric and thermodifferential analysis (DTA/TGA), FT-IR spectroscopy and spectroellipsometry (SE) were used. The tubes have an outer diameter of 0.1-0.2 mu m and length of some microns containing also spherical nanoparticles. The dimensions of the obtained nanotubes are tunable, their diameter and length depending on the synthesis conditions. In the presence of meso-tartaric acid no hollow tubes but nanospheres are obtained. The SiO2 tubes and nanospheres have similar structure but very different morphologies. The large surface area and the distinctive inner and outer surfaces represent a great advantage of the nanotubes over conventional nanoparticles, making these materials suitable for doping and differential functionalization. (C) 2010 Elsevier B.V. All rights reserved.

115. INFLUENCE OF PREPARATION METHOD ON STRUCTURAL PROPERTIES OF GeSiO NANOSYSTEMS

Authors: Stavarache, I; Lepadatu, AM; Teodorescu, V; Stoica, T; Pasuk, I; Stan, G; Iancu, V; Ciurea, ML

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 80, DOI: 10.1109/SMICND.2010.5650255

GeSiO nanosystems were obtained using two different preparation methods, sol-gel and magnetron-sputtering. Transmission electron microscopy measurements were performed to investigate the films structure. Amorphous and crystalline Ge dots embedded in amorphous silicon dioxide were observed. The Ge concentration in the GeSiO films was by Energy-dispersive X-ray spectroscopy.

116. Structural and electrochemical characterization of TiO2/Pt hybrid catalyst system for direct bio-ethanol fuel cell

Authors: Banu, A; Spataru, N; Teodorescu, VS; Maraloiu, AV; Voiculescu, I; Marcu, AM; Spataru, T

Published: MAY 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1193, DOI:

This paper is focused on preparation and microstructure and electrochemical characterization of carbon-TiO2/Pt catalyst used as electrode in fuel cells applications. The platinum deposition was comparatively studied on graphitized carbon substrate and carbon substrate covered with titanium oxide. A strong influence on the platinum deposition, depending of the TiO2 presence, was found. The platinum nanoparticles about 5 nm in size are dispersed in aggregates of 50 to 100 nm on the catalyst surface. This dispersion is strongly affected by the titanium oxide and the substrate porosity. The Pt/TiO2/G and Pt/G electrodes were tested for their catalytic activity in the oxidation of ethanol. The prepared Pt/TiO2/G electrode show higher active surface area than for the Pt/G electrode, this increase in the surface area could be explained to be due to a spreading of wetting or the formation of new active sites at the Pt/oxide interface.

117. Nitridation and crystallization of titanium oxynitride by thermal treatment of TiO2-anatase films in NH3

Authors: Trapalis, C; Calderon-Moreno, JM; Todorova, N; Teodorescu, VS; Stoica, M; Nicolescu, M; Anastasescu, M; Gartner, M; Zaharescu, M

Published: NOV 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1814, DOI:

Nitrogen is often used for doping TiO2 films to improve their photocatalytic properties in visible light. Multilayer TiO2 anatase films were deposited by sol-gel method on quartz substrate and thermally treated in O-2 and NH3 flow in 500-800 degrees C range. The effect of the annealing treatment (temperature and atmosphere) on the structural properties of TiO2 films was studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Nitridation causes the amorphization of the anatase tetragonal phase at 600 degrees C. The film re-crystallization into the cubic oxynitride phase is observed at 800 degrees C. EDX results confirms that the incorporation of nitrogen into the amorphous films takes place before thermally activated growth of the oxynitride phase and demonstrates that the relative O:N composition in the crystalline phase is dependent on the temperature of the thermal treatment.

118. Sol-gel doped TiO2 nanomaterials: a comparative study

Authors: Raileanu, M; Crisan, M; Dragan, N; Crisan, D; Galtayries, A; Braileanu, A; Ianculescu, A; Teodorescu, VS; Nitoi, I; Anastasescu, M

Published: SEP 2009, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 51, 329, DOI: 10.1007/s10971-009-2017-z

Among the great number of sol-gel prepared nanomaterials, TiO2 has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO2 nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO2 and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol-gel Ag-doped TiO2 coatings, prepared by co-gelation and sol-gel Ag-doped TiO2 coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.

119. Synthesis, Mechanism, and Gas-Sensing Application of Surfactant Tailored Tungsten Oxide Nanostructures

Authors: Pokhrel, S; Simion, CE; Teodorescu, VS; Barsan, N; Weimar, U

Published: JUN 9 2009, ADVANCED FUNCTIONAL MATERIALS, 19, 1774, DOI: 10.1002/adfm.200801171

Widely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, H-1, and C-13 NMR spectroscopies, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a=0.7297nm, b=0.7539nm, c=0.7688nm, and beta=90.91 degrees. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15 nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40-60 nm. The investigation of the gas-sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas-sensing properties makes the preparation strategies used interesting candidates for fabricating gas-sensing materials.

120. TiO2-CeO2 Nanometric Powders Prepared by Sol-Gel Method

Authors: Zaharescu, M; Wittmar, A; Teodorescu, V; Andronescu, C; Wittmar, M; Veith, M

Published: 2009, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 635, +, DOI: 10.1002/zaac.200900186

Nanometric powders in the TiO2-CeO2 System were synthesized using sol-gel methods aiming at corrosion inhibitor preparation. The precursors employed were Ti(OiPr)(4) as TiO2 source and Ce(NO3)(3)center dot 6H(2)O or Ce(CH3CO2)(3)center dot xH(2)O as CeO2 source. Several parameters were varied, like the cerium precursor (cerium nitrate or cerium acetate) and the TiO2:CeO2 molar ratios. For both cerium sources binary powders with TiO2:CeO2 = 4:1 or 1:1 molar ratios were prepared. The obtained materials were dried 12 h in an oven at 100 degrees C and then thermally treated for 1 h at 400 degrees C with a heating rate of 1 degrees C.min(-1) in order to eliminate the water and organic residues. In all cases, nanometric - predominantly amorphous - powders have been obtained which crystallized after the I h thermal treatment at 400 degrees C. The only exception was recorded for the TiO2:CeO2 = 4:1 composition prepared from the Ce(NO3)(3)-6H(2)O precursor which remained amorphous after the thermal treatment. Even though the primary particle sizes were similar to 4-5 nm, the material is constituted from aggregates larger than 50 nm. The desired presence of cerium in two valence states, necessary in active corrosion protection, was achieved and it was put into evidence by XPS and DTA/TGA for the TiO2:CeO2 = 4:1 binary compositions. Future studies have to be performed in order to reduce the agglomeration of the material.

121. Fast and Simple Specimen Preparation for TEM Studies of Oxide Films Deposited on Silicon Wafers

Authors: Teodorescu, VS; Blanchin, MG

Published: FEB 2009, MICROSCOPY AND MICROANALYSIS, 15, 19, DOI: 10.1017/S1431927609090011

We present a fast and simple method to prepare specimen,, for transmission electron microscopy Studies of oxide thin films deposited oil silicon Substrates. The method consists of scratching the film surface using I pointed diamond tip, in a special manner. Small and thin fragments are then detached front the film and its substrate. Depending oil the scratching direction, the fragments call be used for plan-view or cross-section imaging. High-resolution images call be also obtained from thin edges of the film fragments. The method is demonstrated in the Case Of HfO2 sol-gel films deposited on [100] Si wafer substrates.

122. Rapidly solidified ferromagnetic shape memory alloys

Authors: Craciunescu, CM; Ercuta, A; Mitelea, I; Valeanu, M; Teodorescu, VS; Lupu, N; Chiriac, H

Published: MAY 2008, EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS, 158, 165, DOI: 10.1140/epjst/e2008-00670-6

Ferromagnetic shape memory alloys have been manufactured by various techniques involving rapid solidification. Bulk alloys have been obtained by extracting the melted alloy in especially designed copper molds; glass coated wires have been obtained by drawing the melt from glass recipients followed by water cooling and ribbons have been fabricated by melt-spinning. Microstructural observations show particular solidification aspects of fractured areas, while ferromagnetic behavior has been detected in glass coated wires obtained by rapid solidification. The martensitic microstructure was observed on Co-Ni-Ga rapid solidified bulk alloys and Fe-Pd ribbons. The memory effect was detected using a Vibran system that allows the detection of the phase transition for the ribbons and by visual observation for other specimens. The conclusions of the observations are related to the comparison between the ferromagnetic behaviors of shape memory alloys solidified using different techniques.

123. Morphology of Si nanocrystallites embedded in SiO2 matrix

Authors: Teodorescu, VS; Ciurea, ML; Iancu, V; Blanchin, MG

Published: NOV 2008, JOURNAL OF MATERIALS RESEARCH, 23, 2995, DOI: 10.1557/JMR.2008.0358

The nanostructure of Si-x(SiO2)(1-x) films deposited on quartz substrate, where x varies from 0 to 1, was determined by high-resolution transmission electron microscopy in the sample regions with x approximate to 0.1, 0.2. 0.5. and 0.75. In the Si-0.5(SiO2)(0.5) region, the formation of a Si nanocrystallite network was established. At high concentrations of Si nanocrystallites, nanotwins and stacking faults occurred in the crystallites. Large Si crystallites appeared at x >= 0.5 in the quartz Substrate under the interface, while the film presented nanopores over the interface. The mechanisms for the formation of the nanocrystallites were discussed and correlated with the film properties.

124. Fe-catalyzed carbon nanotubes growth on fluidized powders by remote radiofrequency plasma beam

Authors: Vizireanu, S; Stoica, D; Birjega, R; Ghica, C; Teodorescu, V; Nistor, L; Ganea, R; Dinescu, G

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2060, DOI:

The paper reports the application of a new method combining the Plasma Assisted Chemical Vapour Deposition with the Fluidized Bed Reactor principles for the production of carbon nanotubes on powdered catalysts. An argon plasma beam injected with acetylene in presence of hydrogen was used as fluidized environment for targeting, smashing and mixing the catalytic powder located on the bottom of a cylindrical quartz reactor. The described technique generated plate-like or fibrous like carbon nanostructures on fine Fe particles and carbon nanotubes with 5-10 nm diameters on Fe supported ZSM-5 zeolite.

125. Nanospinel mixed oxides obtained by self-propagating combustion. Blue cobalt aluminate

Authors: Suciu, C; Mindru, I; Marinescu, G; Patron, L; Carp, O; Teodorescu, VS

Published: OCT 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2707, DOI:

Blue cobalt aluminate was obtained by self-propagating combustion from the system 2Al(NO3)(3)center dot 9H(2)O : 1Co(NO3)(2)center dot 6H(2)O : nNH(2)CH(2)COOH. The precursor was characterized by elemental chemical analysis, IR and UV-Vis spectra and thermal analysis. The CoAl2O4 spinel was characterized by the X-ray diffraction, TEM, IR and UV-Vis spectra.

126. Surfactant involved in Copper Sulfide Nanocrystallites Synthesis

Authors: Simonescu, CM; Teodorescu, VS; Capatina, C

Published: DEC 2008, REVISTA DE CHIMIE, 59, 1329, DOI:

This paper presents the obtaining of copper sulfide CuS (covelite) from Cu(CH3COO)(2)center dot H2O and thioacetamide (TAA) system. The reaction was conducted in presence or absence of sodium-bis(2-ethylhexyl) sulfosuccinate (Na-AOT). The effects of various reaction parameters on the size and on the shape of nanoparticles have been examined. CuS obtained was characterized by X ray diffraction, IR spectroscopy, TEM - transmission electron microscopy and SAED selected area electron diffraction. The influence of surfactant to the shape and size of CuS (covellite) nanocrystals was established. The size of the nanocrystals varied from 10-60 nm depending on the reaction conditions such as quantity of surfactant.

127. Thermal behaviour study of some sol-gel TiO2 based materials

Authors: Crisan, M; Braileanu, A; Crisan, D; Raileanu, M; Dragan, N; Mardare, D; Teodorescu, V; Ianculescu, A; Birjega, R; Dumitru, M

Published: APR 2008, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 92, 13, DOI: 10.1007/s10973-007-8720-5

Among the great number of sol-gel materials prepared, TiO2 holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO2 nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO2 matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania narrosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO2 crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.

128. Structure and dielectric properties of HfO2 films prepared by a sol-gel route

Authors: Blanchin, MG; Canut, B; Lambert, Y; Teodorescu, VS; Barau, A; Zaharescu, M

Published: AUG 2008, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 47, 172, DOI: 10.1007/s10971-008-1758-4

Mono- and multilayer HfO2 sol-gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 degrees C for 0.5 h (after drying at 100 degrees C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 degrees C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 degrees C the films are totally crystallized. The HfO2 grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO2 layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.

129. Correlation between the method of preparation and the properties of the sol-gel HfO2 thin films

Authors: Zaharescu, M; Teodorescu, VS; Gartner, M; Blanchin, MG; Barau, A; Anastasescu, M

Published: JAN 15 2008, JOURNAL OF NON-CRYSTALLINE SOLIDS, 354, 415, DOI: 10.1016/j.jnoncrysol.2007.07.097

This work describes the preparation of HfO2. thin films by the sol-gel method, starting with different precursors such as hafnium ethoxide, hafnium 2,4-pentadionate and hafnium chloride. From the solution prepared as mentioned above, thin films on silicon wafer substrates have been realized by 'dip-coating' with a pulling out speed of 5 cm min(-1). The films densification was achieved by thermal treatment for 10 min at 100 degrees C and 30 min at 450 degrees C or 600 degrees C, with a heating rate of 1 degrees C min(-1). The structural and optical properties of the films are determined employing spectroellipsometric (SE) measurements in the visible range (0.4-0.7 mu m), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The main objective of this paper was to establish a correlation between the method of preparation (precursor, annealing temperature) and the properties of the obtained films. The samples prepared from pentadionate and ethoxide precursors are homogenous and uniform in thickness. The samples prepared starting from chloride precursor are thicker and proved to be less uniform in thickness. Higher non-uniformity develops in multi-deposition films or in crystallized films. A nano-porosity is present in the quasi-amorphous films as well in the crystallized one. For the samples deposited on silicon wafer, the thermal treatment induced the formation of a SiO2 layer at the coating-substrate interface. (C) 2007 Elsevier B.V. All rights reserved.

130. A simple and efficient route to active and dispersed silica supported palladium nanoparticles

Authors: Barau, A; Budarin, V; Caragheorgheopol, A; Luque, R; Macquarrie, DJ; Prelle, A; Teodorescu, VS; Zaharescu, M

Published: AUG 2008, CATALYSIS LETTERS, 124, 214, DOI: 10.1007/s10562-008-9465-x

Various mesoporous silica supported Pd materials were prepared by different methodologies in order to control and optimize the metal nanoparticle sizes for catalytic applications. The catalytic activities (conversion, mol% and selectivity to methyl-cinnamate) of the supported palladium catalysts were investigated in the Heck reaction under microwave irradiation using various haloarenes. Pd materials prepared by co-precipitation exhibited a very poor activity in the Heck reaction compared to that of Pd impregnated samples. Impregnated materials prepared without the use of a specific reducing agent had comparable activities to those of APTS-NaBH4 reduced Pd materials, validating the simplicity of the methodology. High selectivities to methylcinnamate were obtained for all materials.

131. Structure and sensing properties of 0.1SnO(2)-0-9 alpha-Fe2O3 system

Authors: Sorescu, M; Diamandescu, L; Tomescu, A; Tarabasanu-Mihaila, D; Teodorescu, V

Published: JAN 15 2008, MATERIALS CHEMISTRY AND PHYSICS, 107, 131, DOI: 10.1016/j.matchemphys.2007.06.062

The mixed oxide system 0.1SnO(2)-0-9 alpha-Fe2O3 (Sn1) was synthesized using the hydrothermal method and characterized using X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Sensing properties in both CH4 and CO were recorded as a function of temperature, humidity and concentration. The results were compared with those obtained for SnO2 (Sn10). It has been observed that Sn1 displays superior stability and sensitivity for methane as compared to Sn10. For both Sn1 and Sn10, the sensitivity to methane and carbon monoxide is influenced by temperature. In contradistinction to Sn10, Sn1 presents a reduced sensitivity to water vapors. A model based on the simultaneous evaluation of the electrical resistance and workfunction was elaborated to describe the selectivity of Sn1. (c) 2007 Elsevier B.V. All rights reserved.

132. Sequence of phases in the hydrothermal synthesis of zinc-doped magnetite system

Authors: Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, V

Published: DEC 15 2007, MATERIALS CHEMISTRY AND PHYSICS, 106, 278, DOI: 10.1016/j.matchemphys.2007.06.001

Hydrothermal techniques have been used to synthesize samples of ZnxFe3-O-x(4) (x = 0.0-1.0) starting with ZnSO4 center dot 7H(2)O/FeSO4 center dot 7H(2)O aqueous solution. The sequence of phases, structural and magnetic properties were followed by X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Refinement of the XRD spectra yielded the dependence of the lattice parameters of zinc-doped magnetite and zinc ferrite phase as function of the Zn molar concentration x. As well, the particle diameter was derived and represented as a function of Zn content x. As a function of Zn concentration, the phase content of hydrothermally synthesized samples was found to consist of zinc-doped magnetite, goethite and zinc ferrite. Consistent with the XRD results, Mossbauer spectroscopy data indicate the presence of magnetite and goethite at x <= 0.2, magnetite and zinc ferrite at x <= 0.9 and pure zinc ferrite only at high zinc concentrations. The presence of different magnetite phases was confirmed by TEM and particles with a size of 50 nm were identified. Our results show that zinc ferrite is formed at high zinc concentration by the hydrothermal method and an acicular component of goethite-magnetite is obtained at low zinc content. (C) 2007 Elsevier B.V. All rights reserved.

133. Ge dots embedded in silicon dioxide using sol-gel deposition

Authors: Stoica, TF; Gartner, M; Teodorescu, VS; Stoica, T

Published: OCT 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3274, DOI:

A versatile method, that of sol-gel deposition was used to produce Si1-xGexO2 films on Si substrates. Samples after annealing at different temperatures are investigated by different techniques including high-resolution transmission electron microscopy and spectral ellipsometry. It was revealed that, by annealing at high temperatures, Ge accumulates in small clusters (5-10nm) inside of the oxide layer. By ellipsometric investigations, valuable data about the temperature evolution of the composition and optical constants were obtained.

134. Synthesis and characterization of spinelic ferrites obtained from coordination compounds as precursors

Authors: Culita, DC; Patron, L; Teodorescu, VS; Balint, L

Published: APR 25 2007, JOURNAL OF ALLOYS AND COMPOUNDS, 432, 216, DOI: 10.1016/j.jallcom.2006.05.104

Cobalt ferrite and magnetite nanoparticles were obtained by "the complexation method" belonging to soft chemistry, in which cholic acid sodium salt acts as complexation agent. The precursors were characterized by IR, UV-vis spectra and magnetic measurements. X-ray diffraction spectra and transmission electron inicroscopy proved the nanocrystalline structure of the spinelic ferrites. (c) 2006 Elsevier B.V. All rights reserved.

135. TiO2-based nanopowders obtained from different Ti-alkoxides

Authors: Crisan, M; Braileanu, A; Raileanu, M; Crisan, D; Teodorescu, VS; Birjega, R; Marinescu, VE; Madarasz, J; Pokol, G

Published: APR 2007, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 88, 176, DOI: 10.1007/s10973-006-8125-x

Pure TiO2 and S-doped TiO2 sol-gel nanopowders were prepared by controlled hydrolysis-condensation of titanium alkoxides. The influence of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate) used in obtaining TiO2 porous materials in similar conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature of reaction) has been investigated. The relationship between the synthesis conditions and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, BET surface area and the influence of dopant was investigated. The nature of the alkyl group strongly influences the main characteristics of the obtained oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction, TEM and BET surface area measurements.

136. Phototransport and photoluminescence in nanocrystalline porous silicon

Authors: Iancu, V; Ciurea, ML; Stavarache, I; Teodorescu, VS

Published: AUG 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2643, DOI:

The paper presents the phototransport and photoluminescence investigations on nanocrystalline porous silicon. Spectral dependence curves of the phototransport and photoluminescence were taken at room temperature. A typical phototransport curve presents several maxima and shoulders, while the photoluminescence curves present only one maximum. The temperature dependence of the phototransport was measured in the 85 - 250 K range for different wavelengths. All these curves present only one activation energy on the whole temperature interval. The experimental results are interpreted taking into account a quantum confinement model. Previous microstructure investigations proved that the studied nanocrystalline porous silicon is formed by a nanowire network. Then, the electron Hamiltonian can be split into the sum of a 1D longitudinal Bloch part and a 2D transversal part, the nanowire wall acting like a potential well. Thus, a number of discrete energy levels will appear into the band gap. Both phototransport and photoluminescence maxima are due to the transitions between these levels, corresponding to a mean nanowire diameter of 3.2 nm, in good agreement with the previous microstructure and electrical transport investigations. On the contrary, the temperature dependence of the phototransport is determined by the surface states located on the internal surface and/or the interface between nanocrystallites.

137. Thermal behaviour of CuS (covellite) obtained from copper-thiosulfate system

Authors: Simonescu, CM; Teodorescu, VS; Carp, O; Patron, L; Capatina, C

Published: APR 2007, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 88, 76, DOI: 10.1007/s10973-006-8079-z

Thermal behaviour of CuS (covellite) obtained from the Cu(CH3COO)(2)center dot H2O and Na2S2O3 center dot 5H(2)O system, working at different molar ratio (1:6 and 1:4) in presence/absence of NH4VO3, was studied. It was established that the presence of vanadium in the system induces a densification of CuS nodules, but do not change the hexagonal CuS structure. It has an important influence in thermal behaviour of copper sulfide CuS obtained also. The morphological characteristics of CuS play an important role in the thermal stability and the stoichiometry of the thermal decompositions. Also, the possibility to obtain copper sulfides with greater cooper content was investigated.

138. Organic thin film transistors with HfO2 high-k gate dielectric grown by anodic oxidation or deposited by sol-gel

Authors: Tardy, J; Erouej, M; Deman, AL; Gagnalre, A; Teodorescu, V; Blanchin, MG; Canut, B; Barau, A; Zaharescu, M

Published: FEB-MAR 2007, MICROELECTRONICS RELIABILITY, 47, 377, DOI: 10.1016/j.microrel.2006.01.012

We report here on pentacene based organic field effect transistors (OFETs) with a high-k HfO2 gate oxide. HfO2 layers were prepared by two different methods: anodic oxidation and sol-gel. A comparison of the two processes on the electrical properties of OFETs is given. Ultra thin nanoporous (20 nm) sol-gel deposited oxide films were obtained following an annealing at 450 degrees C. They lead to high mobility and stable devices (mu = 0.12 cm(2)/V S). On the other hand, devices with anodic HfO2 revealed a little bit more leaky and show some hysteresis. Anodization, however, presents the advantage of being a fully room temperature process, compatible with plastic substrates. Stability and response to a bias stress are also reported. (c) 2006 Elsevier Ltd. All rights reserved.

139. Electronic transport in Si-SiO2 nanocomposite films

Authors: Ciurea, ML; Teodorescu, VS; Iancu, V; Balberg, I

Published: MAY 20 2006, CHEMICAL PHYSICS LETTERS, 423, 228, DOI: 10.1016/j.cplett.2006.03.070

We report experimental investigations and modeling of the electronic transport in Si-SiO2 nanocomposite films. The current-voltage characteristics measured at room temperature are interpreted as due to high field-assisted tunneling. The activation energies from the current-temperature curves,are given by the energy separations between quantum confinement electronic states, determined from a quantum well model. Consequently, the calculated mean diameter of a nanodot (5.2 nm) is in good agreement with the microstructure data (5 nm). Also, the potential barrier between nanocrystalline Si and amorphous SiO2, previously obtained for nanocrystalline oxidized porous Si (2.2 eV), is confirmed. (c) 2006 Elsevier B.V. All rights reserved.

140. Optical properties of low-dimensional PbI2 particles embedded in polyacrylamide matrix

Authors: Preda, N; Mihut, L; Baltog, I; Velula, T; Teodorescu, V

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 913, DOI:

Small particles of Pbl(2) embedded in transparent polymer matrix have been studied by Raman scattering, UV-VIS absorption spectroscopy, low temperature photoluminescence (PL) and Scanning Electron Microscopy (SEM). The Pbl(2) crystallites were prepared by two different methods: i) by cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide and ii) by chemical reaction of Kl and Pb(NO3)(2) in aqueous polyacrylamide solution. In both cases, beside the hexagonal platelets of Pbl(2) Were identified rods whose luminescence and Raman signature is quite different than of Pbl(2) platelets. Regardless the rods nature, as distinct KPbl(3) particles or lead iodide low-dimensional particles embedded in the polymer matrix, their photoluminescence is featured by an intense green emission (550 nm) appearing at low temperature at excitation wavelengths less then 350 nm.

141. Optical properties of ZnO nanocrystallites embedded in a gold-oxide matrix

Authors: Goldenblum, A; Marian, AB; Teodorescu, V

Published: DEC 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 2132, DOI:

Thin films having ZnO nanocrystallites, with a minimum average size of 2.2 nm, embedded in an amorphous gold oxide matrix have been investigated. These structures do not present a blue-shift of the absorption spectra relative to those corresponding to large ZnO crystallites, a shift which would be expectable for this range of particle size. It was found that the hydrated gold oxide has a much narrower energy gap than ZnO and does not creates quantum wells in the ZnO crystallite region. The Raman spectra present only the confined vibration modes of ZnO. These peculiarities of the mixed system were analyzed by means of an adequate energy band diagram. A Raman resonant effect, determined by interface transitions, has also been detected.

142. Electrical properties of as-grown molecular beam epitaxy high-k gate dielectrics deposited on silicon

Authors: Goldenblum, A; Pintilie, I; Buda, M; Popa, A; Lisca, M; Botila, T; Teodorescu, V; Dimoulas, A; Vellianitis, G

Published: MAR 15 2006, JOURNAL OF APPLIED PHYSICS, 99, DOI: 10.1063/1.2180428

The carrier transport mechanisms in as-grown LaAlO3 and La2Hf2O7 high-k insulator layers deposited on n- and p-Si were deduced from temperature dependent C-V and I-V characteristics correlated with photoelectric measurements. Large, parallel shifts in the high frequency C-V curves are explained by the presence of a large density of interface states and an approximate analytical formula relating the density of states to the C-V shift is deduced. The space charge limited current is explained by the existence of impurity channels situated energetically near the conduction or valence band of silicon.

143. Nanostructured carbon growth by an expanding radiofrequency plasma jet

Authors: Vizireanu, SI; Mitu, B; Birjega, R; Dinescu, G; Teodorescu, V

Published: 2006, CARBON NANOTUBES: FROM BASIC RESEARCH TO NANOTECHNOLOGY, 222, +, DOI:

Carbon deposition from acetylene injection into plasma jet onto sputtered nickel on silicon is investigated. The whole methodology, including the deposition of catalyst, its etching to islands followed by the carbon growth, is implemented in the same reactor. The investigation of structure and morphology shows the formation of nickel particles coated with graphitic layers.

144. Manganese doped sol-gel materials with catalytic properties

Authors: Crisan, M; Raileanu, M; Preda, S; Zaharescu, M; Valean, AM; Popovici, EJ; Teodorescu, VS; Matejec, V; Mrazek, J

Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 819, DOI:

In the present study manganese doped alumina and silica gels and thin films deposited on different substrates (refractory metals, silicon wafers) were obtained by the alkoxide and aqueous routes of the sol-gel method. The characterization of the films was realized by X-ray diffraction (XRD), and spectroellipsometry (SE) methods. The un-supported gels (obtained by the gelation of the solutions used for the film deposition) were characterized by DTA/TG analysis, IR spectroscopy, transmission electron-microscopy and electron diffraction (TEM and SAED) and BET method (adsorption of krypton at temperature of liquid nitrogen) for surface area and pores volume determination. The sol-gel materials were tested as catalysts for the ozone decomposition.

145. Morphology and shape evolution of the copper monosulfide nanocrystallites with the reaction time

Authors: Simonescu, CM; Teodorescu, VS; Brezeanu, M; Melinescu, A

Published: JUN 2005, REVISTA DE CHIMIE, 56, 614, DOI:

Copper monosulfide nanocrystallites have been obtained by reaction between copper acetate and sodium thiosulphate (1:4) at 90 +/- 5 degrees C. The powder was studied by X ray diffraction, IR spectrometry and TEM - transmission electron microscopy and electron diffraction. The copper monosulfide crystallites have been obtained in spherical or discoidal "nodules" which are bonded in much bigger aggregates. The dimensions of the copper monosulfide crystallites are small (10 to 15 nm) near the nucleation center (indicated by an arrow) and bigger at the edges of the spherical nodule (60 to 80 nm). The evolution of the morphology and the shape of the crystallite aggregate with the reaction time allows to propose a nucleation and a crystal growth mechanism for this system.

146. Unconventional method of obtaining nanocrystallites from copper sulfides

Authors: Simonescu, CM; Teodorescu, VE; Patron, L; Giurginca, M; Capatina, C

Published: AUG 2005, REVISTA DE CHIMIE, 56, 812, DOI:

In this article the obtaining and characterization of a mixture of copper sulfide (CuS, Cu9S, CuS2) is presented. The characterization was made by IR Spectroscopy, X-ray Powder Diffraction (XRD) and Transmission Electron Microscopy (TEM). The sulfide mixture represents an aggregate of small particles with an average diameter of 20-30 nm and particles with the diameter of about 500 nm. The smaller particles have the cuboidal morphology and correspond to CuS2; the bigger ones have the hexagonal morphology and correspond to CuS, and Cu9S8.

147. Experiments on pulsed laser deposition and characterization of epitaxially in-situ grown YBa2Cu3O7-x thin films

Authors: Branescu, M; Teodorescu, VS; Socol, G; Balasz, I; Ducu, C; Jaklovszky, J

Published: APR 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 972, DOI:

Experimental results concerning the pulsed laser deposition parameters of in-situ epitaxially grown high crystalline quality YBa2Cu3O7-x thin films are reported. The structural and morphological properties of the deposited films analyzed by transmission electron microscopy, selected area electron diffraction, X-ray diffraction, and Raman spectroscopy are also presented. The YBa2Cu3O7-x thin films, predominantly c-axis oriented had required the smallest oxygen pressure during the cool-down time reported to date.

148. Properties of high-porosity sol-gel derived indium-tin oxide films

Authors: Stoica, TF; Gartner, M; Stoica, T; Losurdo, M; Teodorescu, VS; Blanchin, MG; Zaharescu, M

Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2358, DOI:

Indium-tin oxide (ITO) sol-gel films have been obtained with the void concentration up to 50%. The films are nanostructured with nanocrystals of In2O3:Sn and nanovoids. The information obtained from derivative thermo-gravimetry was used to design the annealing program for ITO film formation with a high void concentration. Multilayer films were obtained by successive deposition. The thickness of one layer was about 9 nm. By successive depositions, the void density of the film is reduced. Quantitative analysis of the void density has been performed by spectroscopic ellipsometry. The conductivity of the films can be varied in a large range by annealing in vacuum or in air, at temperature higher than 200 degrees C.

149. Spectroellipsometric study of the sol-gel nanocrystalline ITO multilayer films

Authors: Stoica, TF; Gartner, M; Losurdo, M; Teodorescu, V; Blanchin, M; Stoica, T; Zaharescu, M

Published: MAY 1 2004, THIN SOLID FILMS, 455, 512, DOI: 10.1016/j.tsf.2003.11.251

Tin-doped indium oxide (ITO) thin films have been deposited by sol-gel process using 'sols' of indium and tin isopropoxides. The thickness of one deposited ITO layer is approximately 50 nm. The desired thickness was obtained by 1-5 successive depositions. The XTEM cross-sectional view of an ITO sample with five depositions showed a clear delimitation of the layers with an alternating structure dense/porous ITO layers. The void fraction in porous regions varies between 20 and 25%. Cubic bixbyite In2O3 nanocrystals with size of 10-20 nm and no phases separation of tin oxide were observed. The optical properties of the films have been investigated by optical transmission and spectroscopic ellipsometry. Reliable optical constants and porosity are obtained only with the model of internal structure based on XTEM results. (C) 2003 Elsevier B.V. All rights reserved.

150. Hydrothermal synthesis and structural characterization of (1-x)alpha-Fe2O3-xSnO(2) nanoparticles

Authors: Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS; Howard, BH

Published: MAY 2004, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 65, 1029, DOI: 10.1016/j.jpcs.2003.10.062

Structural and morphological characteristics of (1 - x)alpha-Fe2O3-xSnO(2) (x = 0.0- 1.0) nanoparticles obtained under hydrothermal conditions have been investigated by X-ray diffraction (XRD), transmission Mossbauer spectroscopy, scanning and transmission electron microscopy as well as energy dispersive X-ray analysis. On the basis of the Rietveld structure refinements of the XRD spectra at low tin concentrations, it was found that Sn4+ ions partially substitute for Fe3+ at the octahedral sites and also occupy the interstitial octahedral sites which are vacant in alpha-Fe2O3 corundum structure. A phase separation of alpha-Fe2O3 and SnO2 was observed for x greater than or equal to 0.4 : the alpha-Fe2O3 Structure containing tin decreases simultaneously with the increase of the SnO2 phase containing substitutional iron ions. The mean particle dimension decreases from 70 to 6 DID, as the molar fraction x increases up to x = 1.0. The estimated solubility limits in the nanoparticle system (1 - x)alpha-Fe2O3-xSnO(2) synthesized under hydrothermal conditions are: x less than or equal to 0.2 for Sn4+ in alpha-Fe2O3 and x greater than or equal to 0.7 for Fe3+ in SnO2. (C) 2003 Elsevier Ltd. All rights reserved.

151. Carbon material deposition by remote RF plasma beam

Authors: Mitu, B; Vizireanu, S; Petcu, C; Dinescu, G; Dinescu, M; Birjega, R; Teodorescu, VS

Published: MAR 1 2004, SURFACE & COATINGS TECHNOLOGY, 180, 243, DOI: 10.1016/j.surfcoat.2003.10.147

Hydrogenated and nitrogenated carbon films were obtained by PECVD with carbon species supplied by acetylene gas injected into an argon or argon/nitrogen remote plasma generated by an expanding radiofrequency discharge. The properties of carbon material like the nature of bonds, morphology, surface topography, crystallinity are presented. The reaction pathways linking the precursors with the depositing species, as revealed by emission spectroscopy, are discussed. (C) 2003 Elsevier B.V. All rights reserved.

152. Microstructure of Si/Sio(2) nanocomposite films

Authors: Teodorescu, VS; Ciurea, ML; Iancu, V; Blanchin, MG

Published: 2004, 2004 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1AND 2, PROCEEDINGS, 62, DOI: 10.1109/SMICND.2004.1402802

The paper presents the inicrostructure of the Si/SiO2 nanocomposite films prepared by co-sputtering from Si and SiO2 targets. High resolution transmission electron microscopy and electron diffraction were used to reveal and compare the structures with different silicon/oxygen (SiOx, 0 < x < 2) coinposition. Si nanocrystallites have been evidenced clearly in the SiO1.6 areas. Percolation limits between the Si crystallites was observed in the x=1 areas. The morphology of the Si nanocrystallites and the amorphous SiO2 zones were compared in regions with different composition.

153. Deposition of hydroxyapatite thin films by Nd : YAG laser ablation: a microstructural study

Authors: Nistor, LC; Ghica, C; Teodorescu, VS; Nistor, SV; Dinescu, M; Matei, D; Frangis, N; Vouroutzis, N; Liutas, C

Published: NOV 2 2004, MATERIALS RESEARCH BULLETIN, 39, 2101, DOI: 10.1016/j.materresbull.2004.07.006

Hydroxyapatite (HA) thin films has been successfully deposited by Nd:YAG laser ablation lambda = 532 nm. The morphology and microstructure of the deposited layers was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). Polycrystalline HA films were directly obtained with the substrate at 300 degreesC and without introducing water vapors in the deposition chamber. Electron paramagnetic resonance (EPR) measurements show that the oxygen stoichiometry in the HA films is also maintained. Depositions performed at lambda = 335 nm laser wavelength and 300 degreesC substrate temperature resulted in polycrystalline layers of mixed composition of HA and tricalciumphosphate (TCP). (C) 2004 Elsevier Ltd. All rights reserved.

154. Nanocrystalline rhombohedral In2O3 synthesized by hydrothermal and postannealing pathways

Authors: Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS

Published: JAN 15 2004, JOURNAL OF MATERIALS SCIENCE, 39, 677, DOI: 10.1023/B:JMSC.0000011529.01603.fc

155. Densification of In2O3: Sn multilayered films elaborated by the dip-coating sol-gel route

Authors: Daoudi, K; Canut, B; Blanchin, MG; Sandu, CS; Teodorescu, VS; Roger, JA

Published: NOV 24 2003, THIN SOLID FILMS, 445, 25, DOI: 10.1016/S0040-6090(03)01061-7

Indium Tin Oxide (ITO) thin films have been deposited by the Sol-Gel Dip-Coating technique, the starting solutions being prepared from chlorides. These multilayered films were crystallized by means of a classical heat treatment at temperatures ranging from 500 to 600 degreesC. Five stacked layers are necessary to obtain a global electrical resistivity value of 2.9 x 10(-3) Omega cm, for 500 degreesC annealed film. The paper focuses on the study of the structure of such multilayered deposits, and on the densification process, using transmission electron microscopy, Rutherford Back-scattering Spectrometry and electrical resistivity measurements. This analysis reveals structural inhomogeneities and different crystallite growth processes as a function of annealing temperature and number of deposited layers. (C) 2003 Elsevier B.V. All rights reserved.

156. Densification and crystallization of SnO2 : Sb sol-gel films using excimer laser annealing

Authors: Sandu, CS; Teodorescu, VS; Ghica, C; Canut, B; Blanchin, MG; Roger, JA; Brioude, A; Bret, T; Hoffmann, P; Garapon, C

Published: MAR 15 2003, APPLIED SURFACE SCIENCE, 208, 387, DOI: 10.1016/S0169-4332(02)01412-5

We have successfully applied laser annealing to sol-gel deposited SnO2:Sb thin films in order to achieve their crystallization. The as-deposited films are quasi-amorphous and electrically non-conductive. After laser annealing they crystallize and become conductive. This paper presents a comparative study of the laser annealed films and shows the influence of the irradiation parameters on the crystallization process and the electrical behavior of the films. Our results are quite promising in view of applying this kind of treatment to films deposited on thermally sensitive substrates (e.g. polymers). (C) 2002 Elsevier Science B.V. All rights reserved.

157. Morphology, structure and optical properties of sol-gel ITO thin films

Authors: Stoica, TF; Teodorescu, VS; Blanchin, MG; Stoica, TA; Gartner, M; Losurdo, M; Zaharescu, M

Published: AUG 15 2003, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 101, 226, DOI: 10.1016/S0921-5107(02)00667-0

The alkoxidic route and the spinning deposition were used to prepare monolayer sol-gel indium tin oxide (ITO) films. The morphology and crystalline structure were investigated by cross-section transmission electron microscopy (XTEM) and atomic force microscopy (AFM). The ITO sol-gel mono-layer contains three regions of different porosities. The basic crystalline structure is that of the In2O3 lattice. The optical properties have been studied by optical transmission and spectroscopic ellipsometry. (C) 2003 Elsevier Science B.V. All rights reserved.

158. Structural properties of sputtered ZnO : Au films

Authors: Goldenblum, A; Teodorescu, V; Wagner, FE; Manaila, R; Filoti, G; Deville, JP; Pantelica, D; Negoita, F; Belu-Marian, A; Scantee, N

Published: JAN 2002, PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82, 204, DOI:

ZnO: Au films have been obtained by a reactive rf magnetron sputtering method using pure Zn and Au targets. Layers with a Au- to- Zn ratio of up to 0. 71 have been deposited. They were analysed by Rutherford back- scattering spectroscopy, elastic recoil detection analysis, transmission electron microscopy, high- resolution electron microscopy, selected- area electron diffraction, X- ray diffraction and Mossbauer spectroscopy. The only crystalline phase found for all investigated Au concentrations was that of ZnO. We conclude that some of the Au enters as interstitial atoms in the compact hexagonal lattice of ZnO being bonded with any three O atoms of the structure and the other part forms an amorphous hydrated gold oxide that coexists with the ZnO crystallites.

159. Nanocapsules of biodegradable polymers: preparation and characterization by direct high resolution electron microscopy

Authors: Guinebretiere, S; Briancon, S; Fessi, H; Teodorescu, VS; Blanchin, MG

Published: SEP 1 2002, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 21, 142, DOI: 10.1016/S0928-4931(02)00073-5

In the field of pharmaceutical applications relying on encapsulation of drug by polymer coating, capsules based on biodegradable polymers with mean size of about 500 nm have been obtained by a patented emulsion-diffusion method. The morphology, size and structure of the nanocapsules (NC) control their pharmaceutical properties, especially release of the drug. Here is reported a decisive contribution of transmission electron microscopy (TEM) in revealing the controlled form and size of the NC: mean size values measured by TEM do agree with data obtained by laser granulometry. Moreover, the TEM magnification allows an estimation of the membrane thickness. (C) 2002 Elsevier Science B.V. All rights reserved.

160. In situ transmission electron microscopy study of Ni silicide phases formed on (001) Si active lines

Authors: Teodorescu, V; Nistor, L; Bender, H; Steegen, A; Lauwers, A; Maex, K; Van Landuyt, J

Published: JUL 1 2001, JOURNAL OF APPLIED PHYSICS, 90, 174, DOI: 10.1063/1.1378812

The formation of Ni silicides is studied by transmission electron microscopy during in situ heating experiments of 12 nm Ni layers on blanket silicon, or in patterned structures covered with a thin chemical oxide. It is shown that the first phase formed is the NiSi2 which grows epitaxially in pyramidal crystals. The formation of NiSi occurs quite abruptly around 400 degreesC when a monosilicide layer covers the disilicide grains and the silicon in between. The NiSi phase remains stable up to 800 degreesC, at which temperature the layer finally fully transforms to NiSi2. The monosilicide grains show different epitaxial relationships with the Si substrate. Ni2Si is never observed. (C) 2001 American Institute of Physics.

161. Kinetics of silver structures growth by electrodiffusion in quartz crystals

Authors: Enculescu, I; Iliescu, B; Teodorescu, V

Published: JAN 2001, SOLID STATE IONICS, 138, 321, DOI: 10.1016/S0167-2738(00)00794-3

Silver layers were grown in quartz crystals by electrodiffusion from an anodic layer of AgNO3. Different experimental arrangements were employed in order to obtain such layers in a reproducible way. We performed DC ionic conductivity measurements on Z-cut and X-cut samples as a function of temperature in the heating up phase and as a function of time at the electromigration temperature. The metal structures and the quartz samples were analyzed by electron microscopy and electron diffraction. Based on the experimental results and on the observations a model, for the metal structure formation is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.

162. The influence of the h-BN morphology and structure on the c-BN growth

Authors: Nistor, L; Teodorescu, V; Ghica, C; Van Landuyt, J; Dinca, G; Georgeoni, P

Published: MAR-JUL 2001, DIAMOND AND RELATED MATERIALS, 10, 1356, DOI: 10.1016/S0925-9635(00)00377-0

The morphology and structure of hexagonal graphitic BN (h-BN) powders with graphitization indices GI <5, used as precursors for the synthesis of cubic BN (c-BN) crystals, has been investigated by transmission electron microscopy in diffraction contrast and high resolution. We show that besides the GI, which is a general parameter for controlling the structural quality of h-EN ponders, some other microstructural features strongly influence the synthesis of c-BN. In our opinion, the high reactivity of some h-BN powders results from the presence of some nucleation centers for c-BN, observed at the edges of the h-BN particles. They are formed by a rearrangement of the graphitic (0002) planes by bending back, joining in pairs and forming locally nanoarches (half nanotubes). In these particular places, the nature of bonding locally turns towards sp(3), as in the case of c-BN, (C) 2001 Elsevier Science B.V. All rights reserved.

163. Internal structure of the nanosized sol-gel ITO thin films

Authors: Stoica, TF; Teodorescu, VS; Blanchin, MG; Stoica, TA; Gartner, M; Zaharescu, M

Published: 2001, 2001 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOL 1 & 2, PROCEEDINGS, 66, DOI:

The alkoxide route and the spinning deposition were used to prepare sol gel ITO films. The morphology and crystalline structure were investigated by Cross-section Transmission Electron Microscopy and Atomic Force Microscopy. The inside of the ITO layer has three regions of different porosity and the basic crystalline structure is that of the In2O3 lattice. Three types of surface morphological structures were found from AFM images.

164. Transmission electron microscopy study of silicon nitride amorphous films obtained by reactive pulsed laser deposition

Authors: Teodorescu, VS; Nistor, LC; Popescu, M; Mihailescu, IN; Gyorgy, E; Van Landuyt, J; Perrone, A

Published: OCT 1 2001, THIN SOLID FILMS, 397, 16, DOI: 10.1016/S0040-6090(01)01408-0

In situ decomposition of silicon nitride films was observed by high-resolution electron microscopy. The films, which were produced by reactive pulsed laser deposition from Si wafer targets at 50-100 Pa ammonia pressure, had a prevalent content of hydrogen-doped, amorphous, non-stoichiometric silicon nitride. A layered morphology of the film, consisting of a density variation in the amorphous structure, developed under electron beam irradiation. This morphology became evident only in cross-sectional observation and was related to the stress-relaxation effect, based on a rearrangement of the bonds, We presume that the stress field anisotropy in the amorphous structure must be related to the presence of some bond texture in the as-grown, amorphous film. (C) 2001 Elsevier Science B.V. All rights reserved.

165. Influence of the deposition configuration on the composition, structure and morphology of La0.6Y0.07Ca0.33Mn3-delta thin films obtained by pulsed laser deposition

Authors: Ghica, C; Valeanu, M; Nistor, LC; Teodorescu, V; Sandu, C; Ristoscu, C; Mihailescu, IN; Werckmann, J; Deville, JP

Published: DEC 2001, INTERNATIONAL JOURNAL OF INORGANIC MATERIALS, 3, 1256, DOI: 10.1016/S1466-6049(01)00153-2

We present a structural and morphological study on La0.6Y0.07Ca0.33MnO3-delta (LYCMO) thin films deposited by laser ablation onto MgO-buffered silicon wafers using two deposition configurations named on-axis and off-axis. All thin films have been deposited at high temperatures in an oxygen atmosphere. A comparative study between the on-axis and off-axis samples is performed by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The films are polycrystalline and show a columnar morphology. The off-axis sample shows a better crystalline texture, although slight compositional variations have been found. (C) 2001 Elsevier Science Ltd. All rights reserved.

166. Structural investigation of a La0.6Y0.07Ca0.33MnO3 thin film by high resolution transmission electron microscopy

Authors: Ghica, C; Nistor, LC; Teodorescu, VS; Valeanu, M; Ristoscu, C; Mihailescu, IN; Deville, JP; Werckmann, J

Published: MAR 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 72, DOI:

The morphology and structure of a La0.6Y0.07Ca0.33MnO3 thin film is studied by transmission electron microscopy. The film was grown by pulsed laser deposition (PLD) on an MgO-buffered silicon <100> wafer. The as-deposited films are polycrystalline and show a columnar morphology. We present a detailed high-resolution transmission electron microscopy structural study concerning a possible monoclinic distortion of the orthorhombic LYCMO crystal cell. (Received February 22, 2000; accepted March 10, 2000).

167. Structural comparison between La0.60Y0.07Ca0.33MnO3-delta bulk and pulsed laser deposited thin films

Authors: Teodorescu, VS; Nistor, LC; Valeanu, M; Ghica, C; Sandu, C; Mihailescu, IN; Ristoscu, C; Deville, JP; Werckmann, J

Published: MAR 2000, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 211, 60, DOI: 10.1016/S0304-8853(99)00713-1

This work is a comparative study of the structural and magneto-transport properties of La0.60Y0.07Ca0.33MnO3-delta (LYCMO) as bulk and thin film. The bulk samples were prepared by solid-state reaction between the corresponding metallic oxides mixed in stoichiometric ratios. The thin film was deposited by pulsed laser deposition on an MgO single crystal using an excimer laser. We show that the structure and stoichiometry of the bulk target are perfectly reproduced in the thin film. We measured the magnetoresistive effect on both the LYCMO pellet and the thin film by using the four-probe technique. The maximum of the MR effect is 680% on the polycrystalline thin film in a 2T magnetic field. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

168. XTEM study of Al doped TiO2 anatase epitaxial films deposited on MgO by pulsed laser deposition

Authors: Teodorescu, VS; Blanchin, MG; Garapon, C; Champeaux, C

Published: NOV 1999, JOURNAL OF MATERIALS SCIENCE, 34, 5476, DOI: 10.1023/A:1004796008417

Al doped TiO2 anatase films epitaxially grown by Pulsed Laser Deposition (PLD) on MgO single crystal substrates have been studied by cross-section transmission electron microscopy. The main structural features of such films are the columnar morphology of the anatase grains and the formation of a spinel buffer layer at the TiO2/MgO interface. The spinel layer is Al rich and displays a steep gradient in Mg composition. Correlation between the microstructure and the optical properties of the films is presented also. (C) 1999 Kluwer Academic Publishers.

169. Transmission electron microscopy study of thin films and surface implanted wafers of LiNbO3

Authors: Teodorescu, VS; Ghica, C; Blanchin, MG; Moretti, P

Published: JUN 1999, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 1, 48, DOI:

Thin films prepared by pulsed laser deposition and single crystal implanted LiNbO3 wafers used in optoelectronic technology were studied by transmission electron microscopy. The use of high electron beam density for high resolution imaging induced a decomposition effect in the implanted LiNbO3 lattice. It is shown that the most probable decomposition leads to the formation of NbO2 nuclei by a topotactic solid state reaction along the pseudo-cubic directions of the lithium niobate matrix. It is also shown that powdered LiNbO3 specimens or samples obtained by preparation of cross section of LiNbO3 thin films are more stable in the electron beam, compared with the samples obtained from implanted LiNbO3 wafers.

170. Microstructural aspects related to carriers transport properties of nanocrystalline porous silicon films

Authors: Ciurea, ML; Teodorescu, VS; Nistor, LC; Blanchin, MG

Published: SEP 1999, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 146, 3521, DOI: 10.1149/1.1392507

A microstructural investigation of porous silicon films, related with a study of carriers transport. is presented. Scanning electron microscopy and conventional transmission electron microscopy with selected area electron diffraction were performed. The films show a double scale porosity: the macroporosity forms an alveolar structure at a micrometric scale and the nanoporosity forms a silicon nanowires network in the alveolar walls and at their surface. Current-voltage characteristics in the -5 to +5 V range and the temperature dependence of dark current in the 150-330 K interval at low voltage were measured. The transport properties are explained by means of a simplified quantum confinement model. Two symmetries of the nanowires, cylindrical and square, are investigated and the differences between them are shown to be insignificant. (C) 1999 The Electrochemical Society. S0013-4651(98)12-109-2. All rights reserved.

171. Irradiation damage in LiNbO3 crystals studied by transmission electron microscopy

Authors: Teodorescu, VS; Blanchin, MG

Published: 1999, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 150, 184, DOI: 10.1080/10420159908226227

Transmission electron microscopy of Er implanted LiNbO3 crystals reveals a structural modification due to the electron bi am irradiation, which consists of the decomposition of LiNbO3 in niobium oxide nanometric size domains. The corresponding electron diffraction patterns do fit at best with the NbO2 simple tetragonal phase. The orientation of the oxide nuclei is along the pseudo-cubic directions of the lithium niobate.

172. Iron-oxide-based nanoparticles produced by pulsed infrared laser pyrolysis of Fe(CO)(5)

Authors: Alexandrescu, R; Morjan, I; Crunteanu, A; Cojocaru, S; Petcu, S; Teodorescu, V; Huisken, F; Kohn, B; Ehbrecht, M

Published: SEP 1 1998, MATERIALS CHEMISTRY AND PHYSICS, 55, 121, DOI: 10.1016/S0254-0584(98)00145-X

The synthesis of nanosized (1-100 nm) particles is an active research field in chemical processing technologies. The process may be of particular relevance in the case of the widely used iron-based materials. In this paper, we report on the preparation and characterization of ultrafine powders produced by pulsed infrared laser pyrolysis of iron pentacarbonyl, Fe(CO)(5), in sensitized mixtures. The synthesis is performed in a flow reactor, at rather high pressure (400 mbar) and high laser fluence (similar to 5 J cm(-2)). The average diameter of the particles is 30 nm. Different characterization methods of the fine powder aged in atmosphere indicate the presence of a substantial oxidic portion, identified as the beta-Fe2O3 . H2O form. Some experimental observations suggest the possibility of iron-oxides formation during synthesis in the flow reactor. The relevant mechanisms for this reaction route are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.

173. XTEM study of Al doped TiO2 anatase epitaxial films deposited on MgO by pulse laser deposition

Authors: Teodorescu, VS; Blanchin, MG; Champeaux, C; Garapon, C

Published: 1998, ELECTRON MICROSCOPY 1998, VOL 2: MATERIALS SCIENCE 1, 658, DOI:

174. Hydrothermal synthesis and structural characterization of some substituted magnetites

Authors: Diamandescu, L; Mihaila-Tarabasanu, D; Teodorescu, V; Popescu-Pogrion, N

Published: DEC 1998, MATERIALS LETTERS, 37, 348, DOI: 10.1016/S0167-577X(98)00117-7

A hydrothermal method has been used to obtain polycrystalline substituted magnetites, Fe3-xMxO4, (M = Cr, Mn, Co, Ni, Cu; 0 less than or equal to x less than or equal to 0.375) starting with ferrous-hi hydroxide mixtures at temperatures up to 300 degrees C. Well-defined magnetite crystallites, 0.2-0.3 mu m in size have been obtained. The appearance of the intermediate phase alpha-FeOOH during hydrothermal transformation into magnetite has been evidenced and discussed. By means of Fe-57 Mossbauer spectroscopy, the distribution of different incorporated cations in the magnetite lattice has been analysed. (C) 1998 Elsevier Science B.V. All rights reserved.

175. Optical and microstructural properties of TiO2(Ni2+) thin films

Authors: Parlog, C; Gartner, M; Osiceanu, P; Teodorescu, V; Moise, F; Ianculescu, A

Published: 1996, CERAMICS INTERNATIONAL, 22, 99, DOI: 10.1016/0272-8842(95)00062-3

Coloured TiO2(Ni2+) thin coatings doped with transitional metals (Ni) were deposited on different substrates (silicon wafers, glass, aluminum) by the sol-gel dip coating process. Complementary techniques (XPS, SE, TEM, XRD, Absorption Spectroscopy) were used to characterize the surface stoichiometry and optical properties, as well as the structure and texture of the thermally treated gels. The presence of fully oxidized film in the outer layers, crystallization in heat treatment to anatase and rutile, formation of porous and coloured films due to the influence of the dopant and the reaction with the substrate, as well as a decrease by three orders of magnitude of the resistivity of Ni-doped films, are reported.

176. RESISTIVITY AND MAGNETORESISTANCE-ELASTORESISTANCE OF POLYCRYSTALLINE NI-SI THIN-FILMS

Authors: BELUMARIAN, A; SERBANESCU, MD; MANAILA, R; TEODORESCU, V; IVANOV, I

Published: FEB 1 1994, THIN SOLID FILMS, 238, 317, DOI: 10.1016/0040-6090(94)90072-8

The temperature dependence of the resistivity and magnetoresistance-elastoresistance of r.f.-sputtered Ni-Si thin films with variable silicon content (0-24 at.%) (determined by Rutherford backscattering spectroscopy) annealed to 300 degrees C was measured. The films, investigated by X-ray diffraction and transmission electron microscopy, exhibit a polycrystalline structure of the Ni f.c.c. type with a disorder degree which increases with the silicon content and a metallic-type conduction mechanism. The ferromagnetic properties of Ni are still preserved in the Ni-Si thin films up to 8.8 at.% silicon content.

177. DYNAMICAL EVOLUTION OF THE SURFACE MICRORELIEF UNDER MULTIPLE-PULSE-LASER IRRADIATION - AN ANALYSIS BASED ON SURFACE-SCATTERED WAVES

Authors: BARBORICA, A; MIHAILESCU, IN; TEODORESCU, VS

Published: MAR 15 1994, PHYSICAL REVIEW B, 49, 8395, DOI: 10.1103/PhysRevB.49.8385

We introduce a theoretical analysis of the temporal and spatial evolution of the surface topography of solids following interference between incident and scattered pulsed laser beams. The essential role played by the nonlinear delayed feedback in the laser-radiation-surface system is considered. We show that it finally determines the surface topography evolution from pulse to pulse. In order to complete the analysis, numerical calculations have been conducted under the hypothesis of strong attenuation of laser radiation into the sample and of a limited heat diffusion during the action of a laser pulse. We predict an evolution from very simple to complex (chaotic) structures under multiple-pulse-laser irradiation of solid surfaces. This evolution is determined by some key irradiation parameters; initial surface microrelief, incident laser intensity, and the number of applied laser pulses. Experiments were performed in order to check the main predictions of the theoretical analysis. The system of transversal excited atmospheric pressure-CO2 laser radiation (lambda = 10.6 mum)-interacting with fused silica was chosen as appropriate for performing test experiments. Optical microscopy studies of laser-treated zones evidenced special modifications of the surface topography in good accordance with the conclusions following from the theoretical analysis. The theoretical analysis is also in good agreement with some available data from the literature, at the same time providing a coherent interpretation of previously unexplained behaviors.

178. SIO2-SM2O3 VITREOUS FILMS VIA THE SOL-GEL METHOD

Authors: ZAHARESCU, M; PIRLOG, C; GARTNER, M; MOISE, F; TEODORESCU, V

Published: AUG 15 1993, JOURNAL OF MATERIALS SCIENCE, 28, 4441, DOI: 10.1007/BF01154953

SiO2-Sm2O3 vitreous films 120 nm thick were obtained via the sol-gel method. Infrared, energy-dispersive analysis of X-rays, spectroscopic ellipsometry and absorption spectroscopy showed a total inclusion of samarium in the silica matrix, which remains amorphous up to 1000-degrees-C. The inclusion of the samarium ion increases the porosity. The optical properties of films were investigated by spectro-ellipsometry, and the parameters obtained were compared with those obtained by other techniques.

179. MORPHOLOGY OF V2O5 PRECIPITATES

Authors: NISTOR, L; SERBAN, S; TEODORESCU, V; VELTERSTEANESCU, M; MANAILA, R; IOVITA, V

Published: APR 1990, REVISTA DE CHIMIE, 41, 385, DOI:

180. SMALL-FIELD BEHAVIOR OF THE CRITICAL CURRENT IN BI2.8PB1.2CA4SR4CU7.2OX CERAMIC SAMPLES ABOVE LIQUID-NITROGEN TEMPERATURE

Authors: MIU, L; ALDICA, G; CRUCEANU, E; TEODORESCU, V

Published: MAY 1990, JOURNAL OF MATERIALS SCIENCE LETTERS, 9, 534, DOI: 10.1007/BF00725868

181. DISTRIBUTION FUNCTION OF PRECIPITATED TIO2 PARTICLE VOLUMES

Authors: MANOLESCU, A; MANAILA, R; MEZINCESCU, GA; NISTOR, L; TEODORESCU, V; SERBAN, S; IOVITA, V

Published: OCT 1990, REVISTA DE CHIMIE, 41, 815, DOI:

The distribution function of precipitated particles in relation to their volume is modelled by a function reproducing the three moments of the real function. The time evolution of the distribution is simulated by the numerical solving of a non-linear differential equation system for the moments, resulting from the rate equation which describes the growth of the particles.

182. MAGNETIC-PROPERTIES AND DEFECTS IN POLYCRYSTALLINE NICKEL FILMS .2. EFFECTS OF ION-IMPLANTATION

Authors: DINCA, G; MANAILA, R; BELUMARIAN, A; NISTOR, LC; TEODORESCU, V; MIU, L

Published: JAN 1 1989, THIN SOLID FILMS, 168, 9, DOI: 10.1016/0040-6090(89)90683-4

183. MAGNETIC-PROPERTIES AND DEFECTS IN POLYCRYSTALLINE NICKEL FILMS .1. MICROSTRUCTURE-RELATED MAGNETIC-ANISOTROPY

Authors: BELUMARIAN, A; MANAILA, R; NISTOR, LC; TEODORESCU, V; DINCA, G; SERBANESCU, D

Published: DEC 15 1988, THIN SOLID FILMS, 167, 12, DOI: 10.1016/0040-6090(88)90476-2

184. PREPARATION OF BARIUM HEXAFERRITE BY A HYDROTHERMAL METHOD - STRUCTURE AND MAGNETIC-PROPERTIES

Authors: BARB, D; DIAMANDESCU, L; RUSI, A; TARABASANUMIHAILA, D; MORARIU, M; TEODORESCU, V

Published: APR 1986, JOURNAL OF MATERIALS SCIENCE, 21, 1122, DOI: 10.1007/BF00553240

185. SEM, SAED, AND TEM INVESTIGATION OF DOMAIN-STRUCTURE IN PZT CERAMICS AT MORPHOTROPIC PHASE-BOUNDARY

Authors: LUCUTA, PG; TEODORESCU, V; VASILIU, F

Published: 1985, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 37, 242, DOI: 10.1007/BF00614823

186. SOLID-SOLUTIONS BASED ON V2O5 .3. PHYSICAL-PROPERTIES

Authors: BURZO, E; STANESCU, L; TEODORESCU, V; CHIPARA, M

Published: 1983, REVISTA DE CHIMIE, 34, 621, DOI:

187. ABOUT THE EXISTENCE OF A LIQUID-PHASE IN THE INTERACTION OF HIGH-POWER PULSED CO2-LASER RADIATION WITH METALLIC TARGETS

Authors: APOSTOL, I; COJOCARU, E; DRAGANESCU, V; MIHAILESCU, IN; NISTOR, L; TEODORESCU, VS

Published: 1981, REVUE ROUMAINE DE PHYSIQUE, 26, &, DOI:

188. COALESCENCE BEHAVIOR OF GOLD PARTICLES VACUUM EVAPORATED ONTO DOPED ALKALI-HALIDE SUBSTRATES

Authors: BIRJEGA, MI; POPESCUPOGRION, N; TEODORESCU, V; TOPA, V

Published: 1979, THIN SOLID FILMS, 57, 269, DOI: 10.1016/0040-6090(79)90161-5

189. STRUCTURAL INVESTIGATION OF IRON-CHROMIUM HIGH-TEMPERATURE SHIFT CONVERSION CATALYST

Authors: FILOTI, G; NISTOR, L; DOCA, I; BRASOVEANU, I; SPANU, V; TEODORESCU, V; ROTARU, P; BLEJOIU, SI

Published: 1979, REVUE ROUMAINE DE CHIMIE, 24, 1105, DOI:

190. NUCLEATION AND GROWTH OF VACUUM EVAPORATED AU DEPOSITS ONTO KI SUBSTRATES

Authors: BIRJEGA, MI; TOPA, V; TEODORESCU, V

Published: 1979, REVUE ROUMAINE DE PHYSIQUE, 24, &, DOI:

191. STUDY OF GROWTH OF VACUUM CONDENSED AU PARTICLES ONTO (100) SURFACES OF KBR KCI AND NACL SUBSTRATES WITH COLLOIDAL CENTERS

Authors: BIRJEGA, MI; TOPA, V; TEODORESCU, V

Published: 1978, STUDII SI CERCETARI DE FIZICA, 30, 196, DOI:

192. NATURE OF BORON-CARBIDE POLYMORPHISM

Authors: ZBEREA, I; TEODORESCU, V

Published: 1978, REVUE ROUMAINE DE PHYSIQUE, 23, 1077, DOI:

193. GROWTH OF KCI SINGLE-CRYSTALS FOR HIGH-POWER CO2-LASER OPTICS

Authors: GHIORDANESCU, V; NISTOR, LC; NISTOR, SV; TEODORESCU, V; VODA, M

Published: 1977, REVUE ROUMAINE DE PHYSIQUE, 22, 666, DOI:

194. ABSORPTION-COEFFICIENT MEASUREMENTS OF KCL BY USING A PULSED CO2-LASER RADIATION SOURCE

Authors: APOSTOL, ID; COJOCARU, E; GHIORDANESCU, V; MIHAILESCU, IN; NISTOR, LC; TEODORESCU, V

Published: 1977, REVUE ROUMAINE DE PHYSIQUE, 22, 883, DOI:

195. STRUCTURE OF GOLD THIN-FILMS EVAPORATED ONTO ALKALI-HALIDE SUBSTRATES WITH COLLOIDAL CENTERS

Authors: BIRJEGA, MI; TOPA, V; TEODORESCU, V

Published: 1976, THIN SOLID FILMS, 32, 211, DOI: 10.1016/0040-6090(76)90292-3

196. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping

Authors: Palade, C; Lepadatu, AM; Slav, A; Cojocaru, O; Iuga, A; Maraloiu, VA; Moldovan, A; Dinescu, M; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: , JOURNAL OF MATERIALS CHEMISTRY C, DOI: 10.1039/d1tc02921e

Dr. Valentin TEODORESCU

Scientific Researcher I

Publications

1. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al2O3/Ge/Al2O3 Memory Structures

2. Enhancing SiGeSn nanocrystals SWIR photosensing by high passivation in nanocrystalline HfO2 matrix

3. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al2O3/Ge/Al2O3 Memory Structures

4. Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization

5. Up-conversion emission in transition metal and lanthanide co-doped systems: dimer sensitization revisited

6. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

7. Titania nanoparticles for photocatalytic degradation of ethanol under simulated solar light

8. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

9. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

10. Lead-Free Perovskite Thin Films with Tailored Pockels-Kerr Effects for Photonics

11. Multifunctional Zn-Doped ITO Sol-Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material

12. The effect of noble metal addition on the properties of oxide semiconductors nanoparticles

13. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites

14. Effect of annealing on the structural, optical and electrical properties of (F, Zn) double doped SnO2 nanoparticles obtained by the laser pyrolysis method

15. SiGeSn Quantum Dots in HfO2 for Floating Gate Memory Capacitors

16. Graphene/Ferroelectric (Ge-Doped HfO2) Adaptable Transistors Acting as Reconfigurable Logic Gates

17. Optical, microstructural and vibrational properties of sol-gel ITO films

18. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping

19. THERMAL BEHAVIOR OF Cu-DOPED TiO2 GELS SYNTHESIZED BY THE SOL-GEL METHOD

20. Advancements on Basic Working Principles of Photo-Driven Oxidative Degradation of Organic Substrates over Pristine and Noble Metal-Modified TiO2. Model Case of Phenol Photo Oxidation

21. Morpho-structural properties of ZnSe, TiO2-ZnSe materials and enzymatic activity of their bioinorganic hybrids with lysozyme

22. Effects of Ge-related storage centers formation in Al2O3 enhancing the performance of floating gate memories

23. Nanocrystallized Ge-Rich SiGe-HfO2 Highly Photosensitive in Short-Wave Infrared

24. Thickness-Dependent Photoelectrochemical Water Splitting Properties of Self-Assembled Nanostructured LaFeO3 Perovskite Thin Films

25. The Influence of the Structural and Morphological Properties of WO3 Thin Films Obtained by PLD on the Photoelectrochemical Water-Splitting Reaction Efficiency

26. GeSn/SiO2 Multilayers by Magnetron Sputtering Deposition for Short-Wave Infrared Photonics

27. Obtaining SiGe nanocrystallites between crystalline TiO2 layers by HiPIMS without annealing

28. Epitaxial GeSn Obtained by High Power Impulse Magnetron Sputtering and the Heterojunction with Embedded GeSn Nanocrystals for Shortwave Infrared Detection

29. Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe-TiO2 Films and Multilayers

30. SiGe nanocrystals in SiO2 with high photosensitivity from visible to short-wave infrared

31. Wafer-scale graphene-ferroelectric HfO2/Ge-HfO2/HfO(2)transistors acting as three-terminal memristors

32. SWIR photoresponse of SiGe/TiO2 multilayers with Ge-rich SiGe nanocrystals

33. Efficacy of annealing and fabrication parameters on photo-response of SiGe in TiO2 matrix

34. GeSn Nanocrystals in GeSnSiO2 by Magnetron Sputtering for Short-Wave Infrared Detection

35. High performance NIR photosensitive films of Ge nanoparticles in Si3N4

36. Fabrication and characterization of Si1-xGex nanocrystals in as-grown and annealed structures: a comparative study

37. Tryptophan/Dextran70 Based-Fluorescent Silver Nanoparticles: Synthesis and Physicochemical Properties

38. Ge nanoparticles in SiO2 for near infrared photodetectors with high performance

39. Orthorhombic HfO2 with embedded Ge nanoparticles in nonvolatile memories used for the detection of ionizing radiation

40. Enhanced photoconductivity of SiGe nanocrystals in SiO2 driven by mild annealing

41. Spherical cobalt/cobalt oxide - Carbon composite anodes for enhanced lithium-ion storage

42. Enhanced photocurrent in GeSi NCs/TiO2 multilayers

43. H2S sensing mechanism of SnO2-CuWO4 operated under pulsed temperature modulation

44. Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

45. Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting

46. Enhanced photocurrent in GeSi NCs / TiO2 multilayers

47. Networked mesoporous SnO2 nanostructures templated by Brij (R) 35 with enhanced H2S selective performance

48. Material parameters from frequency dispersion simulation of floating gate memory with Ge nanocrystals in HfO2

49. GeSi nanocrystals in SiO2 matrix with extended photoresponse in near infrared

50. H2S selective sensitivity of Cu doped BaSrTiO3 under operando conditions and the associated sensing mechanism

51. Influence of preparation conditions on structure and photosensing properties of GeSi/TiO2 multilayers

52. Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors

53. Synthesis, physicochemical characterization and cytotoxic properties of riboflavin loaded Myrj52-silver nanoparticles

54. Sensors based on mesoporous SnO2-CuWO4 with high selective sensitivity to H2S at low operating temperature

55. Photosensitive GeSi/TiO2 multilayers in VIS-NIR

56. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

57. Multiscale investigation of USPIO nanoparticles in atherosclerotic plaques and their catabolism and storage in vivo

58. AMMONIA SENSING WITH 5 MOL% LANTHANUM DOPED BARIUM STRONTIUM TITANATE UNDER HUMID AIR BACKGROUND

59. Thermal analysis of repa-germanium (Ge-132)

60. Ultra-Thin Epitaxial Tungsten Carbide Schottky Contacts in 4H-SiC

61. How morphology determines the charge storage properties of Ge nanocrystals in HfO2

62. Low level NO2 detection under humid background and associated sensing mechanism for mesoporous SnO2

63. Structural and electrical properties of Nb doped TiO2 films prepared by the sol-gel layer-by-layer technique

64. High atomic diffusivity during pulsed laser irradiation of TiON quasi-amorphous films

65. Non-volatile memory structures with Ge NCs-HfO2 intermediate layer

66. Fast atomic diffusion in amorphous films induced by laser pulse annealing

67. Characterization of a n+3C/n-4H SiC heterojunction diode

68. HfO2 with embedded Ge nanocrystals with memory effects

69. Atomic scale elemental mapping of light elements in multilayered perovskite coatings

70. Nanostructuring of GeTiO amorphous films by pulsed laser irradiation

71. NIR to Vis - NIR up - conversion and X-ray excited emission of Er doped high Z BiOCl

72. On the photocatalytic reduction of MU tetrazolium salt on the surface of TiO2 nanoparticles: Formazan production kinetics and mechanism

73. Synthesis of Copper Particles by Non-thermal Atmospheric Pressure Plasma Jet

74. Room temperature ammonia sensing with barium strontium titanate under humid air background

75. Structural, magnetic and catalytic properties of cobalt chromite obtained through precursor method

76. Physicochemical Characterization and In Vitro Cytotoxic Effect of 3-Hydroxyflavone in a Silver Nanoparticles Complex

77. Advanced ceramics in the SnO2-ZnO binary system

1. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al₂O₃/Ge/Al₂O₃ Memory Structures

2. Enhancing SiGeSn nanocrystals SWIR photosensing by high passivation in nanocrystalline HfO₂ matrix

3. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al₂O₃/Ge/Al₂O₃ Memory Structures

9. Ferroelectric Orthorhombic ZrO₂ Thin Films Achieved Through Nanosecond Laser Annealing