NIMP| Valentin-Adrian MARALOIU, Author at NIMP

Education

2006 - 2010 : PhD in Physics, University Claude Bernard Lyon 1, Lyon, France
2007 - 2008 : Master : Imaging of Microstructures; University Claude Bernard Lyon 1, Lyon, France
2004 - 2006 : Master: Optical technologies; University POLITEHNICA of Bucharest
1999 - 2004 : BSc Physics; University POLITEHNICA of Bucharest

Positions

2021 - present : Scientific Researcher 2nd Rank , National Institute of Materials Physics
2016 - 2021 : Scientific Researcher 3rd Rank, National Institute of Materials Physics
2004 - 2016 : Research Assistant, National Institute of Materials Physics

Books

V.A.Maraloiu, M.G.Blanchin, Multiscale study of magnetic nanovectors: Application to USPIO contrast agents for MRI of atherotic inflammation in a murine model, Scholars` Press, 2013; ISBN 978-3-639-70213-2
R.Plugaru, I.Mihalache, R.Gavrila, A.I.Danciu, G.Boldeiu, O.T.Nedelcu, N.Plugaru, V.A.Maraloiu,D.Ghica, M.Stefan, S.V.Nistor, Zinc Oxide thin films for radiation hardened devices by materials engineering, Ed. Academiei Romane, pg. 185-208, 2016; ISBN 978-973-27-2643-3

Patents

OSIM patent application no. RO132066-A0 (Publ. date Jul 28, 2017), “Structura fotosensibila, pe baza de nanocristale de germaniu imersate in dioxid de siliciu, pentru fotodetectori, si procedeu de realizare a acestora”, I. Stavarache, L.M. Ciurea, V. Maraloiu, V.S. Teodorescu

Projects

1. Cytotoxicity and biodegradation of cerium oxide-iron oxide nanoparticle platform as potential theranostic agent for ROS related diseases

Project Type: TE, Start Date: 2022-05-02 End Date: 2024-04-30

2. Structural biotransformations of magnetic nanoparticles in biological environments.

Project Type: PD, Start Date: 2012-01-01 End Date: 2013-12-01

Publications

1. 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.

2. 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

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.

3. 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: MAR 4 2024, JOURNAL OF PHYSICAL CHEMISTRY C, 128, 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.

4. 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

5. 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

6. The Influence of SnO₂ and Noble Metals on the Properties of TiO₂ for Environmental Sustainability

Authors: Goncearenco, E; Morjan, IP; Fleaca, C; Dutu, E; Criveanu, A; Viespe, C; Galca, AC; Maraloiu, AV; Stan, MS; Fort, CI; Scarisoreanu, M

Published: APR 2024, SUSTAINABILITY, 16, 2904, DOI: 10.3390/su16072904

In order to find solutions to current worldwide environmental problems, it is crucial to develop sustainable nanomaterials, ideally with multifunctional properties. Considering this, novel TiO2-SnO2@NMs (noble metals: Au and Ag) composites, for use as sustainable nanomaterials, were successfully prepared via a two-step synthesis process consisting of laser pyrolysis followed by the chemical impregnation of the collected materials with noble metals. The addition of SnO2 favors the transformation of TiO2 from a mixture with a majority Anatase phase to one with a Rutile phase majority. With consideration for their level of environmental toxicity, the features of the synthesized nanomaterials were structurally, morphologically, and optically described and assessed for environmental protection applications as gas sensors and photocatalysts. In the case of the Surface Acoustic Wave sensor, based on a pure TiO2 nanopowder, a notable difference in the frequency shift was detected in comparison to the other examined sensors. All sensors responded to the CH4 concentrations tested (0.02-0.1%). On the other hand, when methyl orange was photodegraded under visible light, the results obtained using NMs for decoration revealed that the photocatalytic activity of TiO2-SnO2@NMs was significantly improved compared to the TiO2-SnO2 binary composite, which already has an enhanced photocatalytic activity, compared to pure TiO2. Overall, this work produces nanoparticles that exhibit better sensory and photocatalytic features, as well as higher levels of biocompatibility with skin cells, for use as eco-friendly nanomaterials for a sustainable future.

7. Nb₂O₅ Microcolumns for Ethanol Sensing

Authors: Kumarage, GWC; Panamaldeniya, SA; Maraloiu, VA; Dassanayake, BS; Gunawardhana, N; Comini, E

Published: MAR 2024, SENSORS, 24, 1851, DOI: 10.3390/s24061851

Pseudohexagonal Nb2O5 microcolumns spanning a size range of 50 to 610 nm were synthesized utilizing a cost-effective hydrothermal process (maintained at 180 degrees C for 30 min), followed by a subsequent calcination step at 500 degrees C for 3 h. Raman spectroscopy analysis unveiled three distinct reflection peaks at 220.04 cm(-1), 602.01 cm(-1), and 735.3 cm(-1), indicative of the pseudohexagonal crystal lattice of Nb2O5. The HRTEM characterization confirmed the inter-lattice distance of 1.8 & Aring; for the 110 plain and 3.17 & Aring; for the 100 plain. The conductometry sensors were fabricated by drop-casting a dispersion of Nb2O5 microcolumns, in ethanol, on Pt electrodes. The fabricated sensors exhibited excellent selectivity in detecting C2H5OH (Delta G/G = 2.51 for 10 ppm C2H5OH) when compared to a variety of tested gases, including CO, CO2, NO2, H-2, H2S, and C3H6O. The optimal operating temperature for this selective detection was determined to be 500 degrees C in a dry air environment. Moreover, the sensors demonstrated exceptional repeatability over the course of three testing cycles and displayed strong humidity resistance, even when exposed to 90% relative humidity. This excellent humidity resistance gas sensing property can be attributed to their nanoporous nature and elevated operating temperature.

8. Bioactive Carbon@CeO₂ Composites as Efficient Antioxidants with Antiamyloid and Radioprotective Potentials

Authors: Shlapa, Y; Siposova, K; Sarnatskaya, V; Drajnova, M; Silvestre-Albero, J; Lykhova, O; Maraloiu, VA; Solopan, SO; Molcan, M; Musatov, A; Belous, A

Published: SEP 25 2024, ACS APPLIED BIO MATERIALS, 7, DOI: 10.1021/acsabm.4c00912

Blending carbon particles (CPs) and nanoscale bioactive cerium dioxide is a promising approach for designing composites for biomedical applications, combining the sorption and antioxidant potentials of each individual component. To address this issue, it is crucial to assess the correlation between the components' ratio, physicochemical parameters, and biofunctionality of the composites. Thus, the current research was aimed at fabricating C@CeO2 composites with different molar ratios and the examination of how the parameters of the composites affect their bioactivity. XRD, X-ray photoelectron spectroscopy, and electron microscopy data verified the formation of C@CeO2 composites. CeO2 nanoparticles (NPs) of 4-6 nm are highly dispersed on the surfaces of amorphous CPs. The presence of CeO2 NPs on the carbon surface decreased its adsorption potential in a dose-dependent manner. Besides, the coexistence of carbon and CeO2 in a single composite promotes some redox interactions between O-functionalities and Ce3+/Ce4+ species, resulting in changes in the chemical state of the surface of the composites. These observations suggest the strong connection between these parameters and the biofunctionality of the composites. The presence of CeO2 NPs on the surface of carbon led to a significant increase in the stability of the prepared composites in their aqueous suspensions. The enhancement of bioactivity of the newly prepared C@CeO2 compared to bare carbon and CeO2 was validated by testing their pseudomimetic (catalase/peroxidase-like and superoxide dismutase-like), antiamyloid, and radioprotective activities.

9. Fabrication of CuO (p)-ZnO (n) Core-Shell Nanowires and Their H₂-Sensing Properties

Authors: Sisman, O; Zappa, D; Maraloiu, VA; Comini, E

Published: JUL 2023, MATERIALS, 16, 4802, DOI: 10.3390/ma16134802

Unlike the conventional one-dimensional (1D) core-shell nanowires (NWs) composed of p-type shells and n-type cores, in this work, an inverse design is proposed by depositing n-type ZnO (shell) layers on the surface of p-type CuO (core) NWs, to have a comprehensive understanding of their conductometric gas-sensing kinetics. The surface morphologies of bare and core-shell NWs were investigated by field emission scanning electron microscope (FE-SEM). The ZnO shell layer was presented by overlay images taken by electron dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HRTEM). The pronounced crystalline plane peaks of ZnO were recorded in the compared glancing incident X-ray diffraction (GI-XRD) spectra of CuO and CuO-ZnO core-shell NWs. The ZnO shell layers broaden the absorption curve of CuO NWs in the UV-vis absorption spectra. As a result of the heterostructure formation, the intrinsic p-type sensing behavior of CuO NWs towards 250 and 500 ppm of hydrogen (H-2) switched to n-type due to the deposition of ZnO shell layers, at 400 & DEG;C in dry airflow.

10. Revolutionizing n-type Co₃O₄ Nanowire for Hydrogen Gas Sensing

Authors: Kumarage, GWC; Zappa, D; Mihalcea, CG; Maraloiu, VA; Stefan, M; Comini, E

Published: 2023 JUL 27 2023, ADVANCED ENERGY AND SUSTAINABILITY RESEARCH, DOI: 10.1002/aesr.202300067

This study presents conductometric sensors based on Co3O4 nanowires for hydrogen detection at ppb levels. The nanowires are synthesized through thermal oxidation of a 50 nm cobalt layer, exhibiting diameters between 6-50 nm and lengths of 1-5 & mu;m, primarily growing along the (311) direction of spinal Co3O4. Raman investigation reveals five characteristic peaks at 195, 482, 521, 620, and 692 cm(-1), corresponding to symmetric phonon modes of crystalline Co3O4. Electron paramagnetic resonance measurements confirm the presence of a ferromagnetic phase, attributed to incomplete cobalt oxidation, which disappears after 8 h of thermal aging at 400 & DEG;C. Conductometry measurements are performed in the temperature range of 300-500 & DEG;C. At temperatures above 300 & DEG;C, sensors exhibit abnormal n-type semiconducting behavior due to lattice oxygen's involvement in the hydrogen sensing mechanism. Operating at 450 & DEG;C in dry air, the sensor shows a higher 232% response to 100 ppm H-2 compared to ethanol, acetone, methane, carbon monoxide, and nitrogen dioxide. Remarkably, the sensor maintains a consistent conductance baseline even under high humidity (90%) for 25 d, with three-cycle repeatability. This distinctive gas-sensing capability is attributed to the catalytic activity and elevated operating temperature.

11. Nanoscale Y3AlFe4O12 garnets: Looking into subtle features of crystalline structure and properties formation

Authors: Solopan, S; Tovstolytkin, A; Zamorskyi, V; Shlapa, Y; Maraloiu, VA; Fedorchuk, O; Belous, A

Published: DEC 15 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 968, 172248, DOI: 10.1016/j.jallcom.2023.172248

Nanoscale Al-doped yttrium-iron garnets attract enhanced scientific and practical interest in the development of microwave devices due to their remarkable physical-chemical properties, which depend essentially on the method and conditions of synthesis. This work highlights the advantages of a specific two-stage synthesis of Y3AlFe4O12 garnet ferrite nanoparticles by the precipitation in aqueous solutions and deals with the detailed examinations of the precipitates obtained during this process. The results of the complex studies using high resolution transmission microscopy, dynamic light scattering and magnetic measurements have allowed assessing the features of the formation of crystalline structure. It is demonstrated that the sequence of the precipitation of components during the synthesis strongly affects the physical-chemical properties of the formed precipitate (filtration coefficient value, surface charge, micelle's structure) as well as the physical properties of nanoparticles obtained after their heat treatment at 800 degrees C (saturation magnetization, coercive force). Simultaneous precipitation of Fe(OH)3 and Al(OH)3 metal hydroxides, which form one of three crystallographic sub lattices of the garnet structure, at the first stage of the synthesis of ferrite-garnets is revealed to provide higher values of filtration coefficient of the formed precipitate and better technological and physical-chemical parameters of the fabricated garnet nanoparticles that makes this method highly advantageous for industrial application.

12. Burdock-Derived Composites Based on Biogenic Gold, Silver Chloride and Zinc Oxide Particles as Green Multifunctional Platforms for Biomedical Applications and Environmental Protection

Authors: Zgura, I; Badea, N; Enculescu, M; Maraloiu, VA; Ungureanu, C; Barbinta-Patrascu, ME

Published: FEB 2023, MATERIALS, 16, 1153, DOI: 10.3390/ma16031153

Green nanotechnology is a rapidly growing field linked to using the principles of green chemistry to design novel nanomaterials with great potential in environmental and health protection. In this work, metal and semiconducting particles (AuNPs, AgClNPs, ZnO, AuZnO, AgClZnO, and AuAgClZnO) were phytosynthesized through a "green" bottom-up approach, using burdock (Arctium lappa L.) aqueous extract. The morphological (SEM/TEM), structural (XRD, SAED), compositional (EDS), optical (UV-Vis absorption and FTIR spectroscopy), photocatalytic, and bio-properties of the prepared composites were analyzed. The particle size was determined by SEM/TEM and by DLS measurements. The phytoparticles presented high and moderate physical stability, evaluated by zeta potential measurements. The investigation of photocatalytic activity of these composites, using Rhodamine B solutions' degradation under solar light irradiation in the presence of prepared powders, showed different degradation efficiencies. Bioevaluation of the obtained composites revealed the antioxidant and antibacterial properties. The tricomponent system AuAgClZnO showed the best antioxidant activity for capturing ROS and ABTS center dot(+) radicals, and the best biocidal action against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The "green" developed composites can be considered potential adjuvants in biomedical (antioxidant or biocidal agents) or environmental (as antimicrobial agents and catalysts for degradation of water pollutants) applications.

13. Influence of Ferroelectric Filler Size and Clustering on the Electrical Properties of (Ag-BaTiO3)-PVDF Sub-Percolative Hybrid Composites

Authors: Padurariu, L; Horchidan, N; Ciomaga, CE; Curecheriu, LP; Lukacs, VA; Stirbu, RS; Stoian, G; Botea, M; Florea, M; Maraloiu, VA; Pintilie, L; Rotaru, A; Mitoseriu, L

Published: JAN 2023, ACS APPLIED MATERIALS & INTERFACES, DOI: 10.1021/acsami.2c15641

The paper presents a study concerning the role of ferroelectric filler size and clustering in the dielectric properties of 20%BaTiO3-80%PVDF and of 20% (2%Ag-98%BaTiO3)-PVDF hybrid nanocomposites. By finite element calculations, it was shown that using fillers with epsilon > 103 does not provide a permittivity rise in the composites and the effective dielectric constant tends to saturate to specific values determined by the filler size and agglomeration degree. Irrespective of the ferroelectric filler sizes, the addition of metallic ultrafine nanoparticles (Ag) results in permittivity intensification and the effect is even stronger if the metallic nanoparticles are connected to a higher degree with the ferroelectric particles' surfaces. When using coarse ferroelectric fillers, the probability of clustering is higher, thus favoring the permittivity increase by field concentration in small regions close to the interfaces separating dissimilar materials. The modeling results were validated by an experimental dielectric analysis performed in a series of PVDF-based thick films with the same amount of BaTiO3 fillers or with Ag-BaTiO3 hybrid fillers. Similar trends as predicted by simulations were found experimentally but with slightly higher permittivity values which were assigned to the modifications of the polymer phase composition due to the presence of nanofillers and the local sample inhomogeneity (the presence of clustering, in particular for coarse BaTiO3 grains), which create regions with enhanced local fields.

14. Antibacterial Activity of PVA Hydrogels Embedding Oxide Nanostructures Sensitized by Noble Metals and Ruthenium Dye

Authors: Pelinescu, D; Anastasescu, M; Bratan, V; Maraloiu, VA; Negrila, C; Mitrea, D; Calderon-Moreno, J; Preda, S; Gifu, IC; Stan, A; Ionescu, R; Stoica, I; Anastasescu, C; Zaharescu, M; Balint, I

Published: AUG 2023, GELS, 9, 650, DOI: 10.3390/gels9080650

Nanostructured oxides (SiO2, TiO2) were synthesized using the sol-gel method and mod-ified with noble metal nanoparticles (Pt, Au) and ruthenium dye to enhance light harvesting and promote the photogeneration of reactive oxygen species, namely singlet oxygen (O-1(2)) and hydroxyl radical (center dot OH). The resulting nanostructures were embedded in a transparent polyvinyl alcohol (PVA) hydrogel. Morphological and structural characterization of the bare and modified oxides was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Additionally, electrokinetic potential measurements were conducted. Crystallinity data and elemental analysis of the investigated systems were obtained through X-ray diffraction and X-ray fluorescence analyses, while the chemical state of the elements was determined using XPS. The engineered ma-terials, both as simple powders and embedded in the hydrogel, were evaluated for their ability to generate reactive oxygen species (ROS) under visible and simulated solar light irradiation to establish a correlation with their antibacterial activity against Staphylococcus aureus. The generation of singlet oxygen (O-1(2)) by the samples under visible light exposure can be of significant importance for their potential use in biomedical applications.

15. Influence of Ferroelectric Filler Size and Clustering on the Electrical Properties of (Ag-BaTiO3)-PVDF Sub-Percolative Hybrid Composites

Authors: Padurariu, L; Horchidan, N; Ciomaga, CE; Curecheriu, LP; Lukacs, VA; Stirbu, RS; Stoian, G; Botea, M; Florea, M; Maraloiu, VA; Pintilie, L; Rotaru, A; Mitoseriu, L

Published: 2023 JAN 18 2023, ACS APPLIED MATERIALS & INTERFACES, DOI: 10.1021/acsami.2c15641

16. Design of Magnetic Fe₃O₄/CeO₂ "Core/Shell"-Like Nanocomposites with Pronounced Antiamyloidogenic and Antioxidant Bioactivity

Authors: Shlapa, Y; Siposova, K; Veltruska, K; Maraloiu, VA; Garcarova, I; Rajnak, M; Musatov, A; Belous, A

Published: OCT 12 2023, ACS APPLIED MATERIALS & INTERFACES, 15, DOI: 10.1021/acsami.3c10845

Core/shell nanocomposites based on magnetic magnetite (Fe3O4) and redox-active cerium dioxide (CeO2) nanoparticles (NPs) are promising in the field of biomedical interests because they can combine the ability of magnetic NPs to heat up in an alternating magnetic field (AMF) with the pronounced antioxidant activity of CeO2 NPs. Thus, this report is devoted to Fe3O4/CeO2 nanocomposites (NCPs) synthesized by precipitation of the computed amount of "CeO2-shell" on the surface of prefabricated Fe3O4 NPs. The X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy data validated the formation of Fe3O4/CeO2 "core/shell"-like NCPs, in which ultrafine CeO2 NPs with an average size of approximately 3-3.5 nm neatly surround Fe3O4 NPs. The presence of a CeO2 "shell" significantly increased the stability of Fe3O4/CeO2 NCPs in aqueous suspensions: Fe3O4/CeO2 NCPs with "shell thicknesses" of 5 and 7 nm formed highly stable magnetic fluids with zeta-potential values of >+30 mV. The magnetization values of Fe3O4/CeO2 NCPs decreased with a growing CeO2 "shell" around the magnetic NPs; however, the resulting composites retained the ability to heat efficiently in an AMF. The presence of a CeO2 "shell" generates a possibility to precisely regulate tuning of the maximum heating temperature of magnetic NCPs in the 42-50 degrees C range and stabilize it after a certain time of exposure to an AMF by changing the thickness of the "CeO2-shell". A great improvement was observed in both antioxidant and antiamyloidogenic activities. It was found that inhibition of insulin amyloid formation, expressed in IC50 concentration, using NCPs with a "shell thickness" of 7 nm was approximately 10 times lower compared to that of pure CeO2. For these NCPs, more than 2 times higher superoxide dismutase-like activity was observed. The coupling of both Fe3O4 and CeO2 results in higher bioactivity than either of them individually, probably due to a synergistic catalytic mechanism.

17. Synthesis and Anti-Melanoma Activity of L-Cysteine-Coated Iron Oxide Nanoparticles Loaded with Doxorubicin

Authors: Toderascu, LI; Sima, LE; Orobeti, S; Florian, PE; Icriverzi, M; Maraloiu, VA; Comanescu, C; Iacob, N; Kuncser, V; Antohe, I; Popescu-Pelin, G; Stanciu, G; Ionita, P; Mihailescu, CN; Socol, G

Published: FEB 2023, NANOMATERIALS, 13, 621, DOI: 10.3390/nano13040621

In this study, we report on the synthesis of L-Cysteine (L-Cys)-coated magnetic iron oxide nanoparticles (NPs) loaded with doxorubicin (Dox). The Fe3O4-L-Cys-Dox NPs were extensively characterized for their compositional and morpho-structural features using EDS, SAED, XRD, FTIR and TEM. XPS, Mossbauer spectroscopy and SQUID measurements were also performed to determine the electronic and magnetic properties of the Fe3O4-L-Cys-Dox nanoparticles. Moreover, by means of a FO-SPR sensor, we evidenced and confirmed the binding of Dox to L-Cys. Biological tests on mouse (B16F10) and human (A375) metastatic melanoma cells evidenced the internalization of magnetic nanoparticles delivering Dox. Half maximum inhibitory concentration IC50 values of Fe3O4-L-Cys-Dox were determined for both cell lines: 4.26 mu g/mL for A375 and 2.74 mu g/mL for B16F10, as compared to 60.74 and 98.75 mu g/mL, respectively, for unloaded controls. Incubation of cells with Fe3O4-L-Cys-Dox modulated MAPK signaling pathway activity 3 h post-treatment and produced cell cycle arrest and increased apoptosis by 48 h. We show that within the first 2 h of incubation in physiological (pH = 7.4) media, similar to 10-15 mu M Dox/h was released from a 200 mu g/mL Fe3O4-L-Cys-Dox solution, as compared to double upon incubation in citrate solution (pH = 3), which resembles acidic environment conditions. Our results highlight the potential of Fe3O4-L-Cys-Dox NPs as efficient drug delivery vehicles in melanoma therapy.

18. Synthesis of TiO₂-(B) Nanobelts for Acetone Sensing

Authors: Kumarage, GWC; Panamaldeniya, SA; Maddumage, DC; Moumen, A; Maraloiu, VA; Mihalcea, CG; Negrea, RF; Dassanayake, BS; Gunawardhana, N; Zappa, D; Galstyan, V; Comini, E

Published: OCT 2023, SENSORS, 23, 8322, DOI: 10.3390/s23198322

Titanium dioxide nanobelts were prepared via the alkali-hydrothermal method for application in chemical gas sensing. The formation process of TiO2-(B) nanobelts and their sensing properties were investigated in detail. FE-SEM was used to study the surface of the obtained structures. The TEM and XRD analyses show that the prepared TiO2 nanobelts are in the monoclinic phase. Furthermore, TEM shows the formation of porous-like morphology due to crystal defects in the TiO2-(B) nanobelts. The gas-sensing performance of the structure toward various concentrations of hydrogen, ethanol, acetone, nitrogen dioxide, and methane gases was studied at a temperature range between 100 and 500 C-degrees. The fabricated sensor shows a high response toward acetone at a relatively low working temperature (150 C-degrees), which is important for the development of low-power-consumption functional devices. Moreover, the obtained results indicate that monoclinic TiO2-B is a promising material for applications in chemo-resistive gas detectors.

19. 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.

20. Memory Properties of Zr-Doped ZrO2 MOS-like Capacitor

Authors: Palade, C; Slav, A; Stavarache, I; Maraloiu, VA; Negrila, C; Ciurea, ML

Published: SEP 2022, COATINGS, 12, 1369, DOI: 10.3390/coatings12091369

The high-k-based MOS-like capacitors are a promising approach for the domain of non-volatile memory devices, which currently is limited by SiO2 technology and cannot face the rapid downsizing of the electronic device trend. In this paper, we prepare MOS-like trilayer memory structures based on high-k ZrO2 by magnetron sputtering, with a 5% and a 10% concentrations of Zr in the Zr-ZrO2 floating gate layer. For crystallization of the memory structure, rapid thermal annealing at different temperatures between 500 degrees C and 700 degrees C was performed. Additionally, Al electrodes were deposited in a top-down configuration. High-resolution transmission electron microscopy reveals that ZrO2 has a polycrystalline-columnar crystallization and a tetragonal crystalline structure, which was confirmed by X-ray diffraction measurements. It is shown that the tetragonal phase is stabilized during the crystallization by the fast diffusion of oxygen atoms. The capacitance-voltage characteristics show that the widest memory window (Delta V = 2.23 V) was obtained for samples with 10% Zr annealed at 700 degrees C for 4 min. The charge retention characteristics show a capacitance decrease of 36% after 10 years.

21. Increasing Permittivity and Mechanical Harvesting Response of PVDF-Based Flexible Composites by Using Ag Nanoparticles onto BaTiO3 Nanofillers

Authors: Horchidan, N; Ciomaga, CE; Curecheriu, LP; Stoian, G; Botea, M; Florea, M; Maraloiu, VA; Pintilie, L; Tufescu, FM; Tiron, V; Rotaru, A; Mitoseriu, L

Published: MAR 2022, NANOMATERIALS, 12, 934, DOI: 10.3390/nano12060934

The role of Ag addition on the structural, dielectric, and mechanical harvesting response of 20%(xAg - (1 - x)BaTiO3) - 80%PVDF (x = 0, 2, 5, 7 and 27 vol.%) flexible composites is investigated. The inorganic fillers were realized by precipitating fine (similar to 3 nm) silver nanoparticles onto BaTiO3 nanoparticles (similar to 60 nm average size). The hybrid admixtures with a total filling factor of 20 vol.% were embedded into the PVDF matrix. The presence of filler enhances the amount of beta-PVDF polar phase and the BaTiO3 filler induces an increase of the permittivity from 11 to 18 (1 kHz) in the flexible composites. The addition of increasing amounts of Ag is further beneficial for permittivity increase; with the maximum amount (x = 27 vol.%), permittivity is three times larger than in pure PVDF (epsilon(r) similar to 33 at 1 kHz) with a similar level of tangent losses. This result is due to the local field enhancement in the regions close to the filler-PVDF interfaces which are additionally intensified by the presence of silver nanoparticles. The metallic addition is also beneficial for the mechanical harvesting ability of such composites: the amplitude of the maximum piezoelectric-triboelectric combined output collected in open circuit conditions increases from 0.2 V/cm(2) (PVDF) to 30 V/cm(2) for x = 27 vol.% Ag in a capacitive configuration. The role of ferroelectric and metallic nanoparticles on the increasing mechanical-electric conversion response is also been explained.

22. Facile synthesis of low toxicity iron oxide/TiO2 nanocomposites with hyperthermic and photo-oxidation properties

Authors: Popescu, T; Matei, CO; Culita, DC; Maraloiu, VA; Rostas, AM; Diamandescu, L; Iacob, N; Savopol, T; Ilas, MC; Feder, M; Lupu, AR; Iacoban, AC; Vlaicu, ID; Moisescu, MG

Published: APR 27 2022, SCIENTIFIC REPORTS, 12, 6887, DOI: 10.1038/s41598-022-11003-3

The present study aimed to assess the feasibility of developing low-cost multipurpose iron oxide/TiO2 nanocomposites (NCs) for use in combined antitumor therapies and water treatment applications. Larger size (approximate to 100 nm) iron oxide nanoparticles (IONPs) formed magnetic core-TiO2 shell structures at high Fe/Ti ratios and solid dispersions of IONPs embedded in TiO2 matrices when the Fe/Ti ratio was low. When the size of the iron phase was comparable to the size of the crystallized TiO2 nanoparticles (approximate to 10 nm), the obtained nanocomposites consisted of randomly mixed aggregates of TiO2 and IONPs. The best inductive heating and ROS photogeneration properties were shown by the NCs synthesized at 400 degrees C which contained the minimum amount of alpha-Fe2O3 and sufficiently crystallized anatase TiO2. Their cytocompatibility was assessed on cultured human and murine fibroblast cells and analyzed in relation to the adsorption of bovine serum albumin from the culture medium onto their surface. The tested nanocomposites showed excellent cytocompatibility to human fibroblast cells. The results also indicated that the environment (i.e. phosphate buffer or culture medium) used to disperse the nanomaterials prior to performing the viability tests can have a significant impact on their cytotoxicity.

23. 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.

24. Properties of Ni0.5Zn0.5Fe2O4 nanoparticles with the spinel structure synthesized via cryo-chemical method

Authors: Timashkov, I; Shlapa, Y; Maraloiu, VA; Rajnak, M; Timko, M; Belous, A

Published: SEP 2021, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 127, DOI: 10.1007/s00339-021-04795-0

Ni0.5Zn0.5Fe2O4 nanoparticles (NPs) with the spinel structure were synthesized by the cryo-chemical method with further heat treatment in the temperature range of 200-800 degrees C. Crystalline NPs began to form in one-stage and the degree of crystallinity grew with the increase of the heating temperature. Particles sizes, their size distributions and magnetization also tended to growth directly with the increasing the heating temperature of NPs. Magnetic fluids based on the obtained Ni0.5Zn0.5Fe2O4 NPs demonstrated effective and self-controlled heating up to the certain temperatures under the effect of an alternating magnetic field in contrast to known in literature Fe3O4 NPs with the spinel structure, which heated up uncontrolled to the extremely high phase transition temperature.

25. Experimental tuning of AuAg nanoalloy plasmon resonances assisted by machine learning method

Authors: Koziol, R; Lapinski, M; Syty, P; Sadowski, W; Sienkiewicz, JE; Nurek, B; Maraloiu, VA; Koscielska, B

Published: NOV 30 2021, APPLIED SURFACE SCIENCE, 567, DOI: 10.1016/j.apsusc.2021.150802

Plasmonic nanostructures based on AuAg nanoalloys were fabricated by thermal annealing of metallic films in an argon atmosphere. The nanoalloys were chosen because they can extend the wavelength range in which plasmon resonance occurs and thus allow the design of plasmonic platforms with the desired parameters. The influence of initial fabrication parameters and experimental conditions on the formation of nanostructures was investigated. For the surface morphology studies, chemical composition analysis and nanograin structure, Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), Energy Dispersive X-Ray Spectroscopy (EDS) and High-Resolution Transmission Electron Microscopy (HR TEM) measurements were performed. The position of the resonance band was successfully tuned in the 100 nm range. The EDS together with the XPS analysis confirmed the formation of an alloy with the aspect ratio of individual metals in a single nanoisland similar to the ratio of the thicknesses of the initially sputtered layers. The experimental research was complemented by the neural network model, which enables the calculation of the absorbance peak depending on the thickness of Au and Ag layers and the annealing time. The proposed model of machine learning makes it possible to fine-tune the desired position of the plasmon resonance.

26. Biocompatible Silver Nanoparticles: Study of the Chemical and Molecular Structure, and the Ability to Interact with Cadmium and Arsenic in Water and Biological Properties

Authors: Bertela, F; Marsotto, M; Meneghini, C; Burratti, L; Maraloiu, VA; Iucci, G; Venditti, I; Prosposito, P; D'Ezio, V; Persichini, T; Battocchio, C

Published: OCT 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11102540

In the field of research for designing and preparing innovative nanostructured systems, these systems are able to reveal the presence of heavy metals in water samples, and can efficiently and selectively interact with them, allowing for future applications in the field of water remediation. We investigated the electronic and molecular structure, as well as the morphology, of silver nanoparticles stabilized by mixed biocompatible ligands (the amino acid L-cysteine and the organic molecule citrate) in the presence of cadmium and arsenic ions. The molecular, electronic, and local structure at the ligands/silver nanoparticles interface was probed by the complementary synchrotron radiation-induced techniques (SR-XPS, NEXAFS and XAS). The optical absorption (in the UV-Vis range) of the nanosystem was investigated in the presence of Cd(II) and As(III) and the observed behavior suggested a selective interaction with cadmium. In addition, the toxicological profile of the innovative nanosystem was assessed in vitro using a human epithelial cell line HEK293T. We analyzed the viability of the cells treated with silver nanoparticles, as well as the activation of antioxidant response.

27. 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.

28. 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.

29. Mesoporous TiO2 from Metal-Organic Frameworks for Photoluminescence-Based Optical Sensing of Oxygen

Authors: Alfe, M; Gargiulo, V; Amati, M; Maraloiu, VA; Maddalena, P; Lettieri, S

Published: JUL 2021, CATALYSTS, 11, DOI: 10.3390/catal11070795

Metal-organic frameworks (MOFs) are a class of porous coordination networks extraordinarily varied in physicochemical characteristics such as porosity, morphologies, and compositions. These peculiarities make MOFs widely exploited in a large array of applications, such as catalysis, chemicals and gas sensing, drug delivery, energy storage, and energy conversion. MOFs can also serve as nanostructured precursors of metal oxides with peculiar characteristics and controlled shapes. In this work, starting from MIL125-(Ti), a 1,4-benzenedicarboxylate (BDC)-based MOF with Ti as metallic center, mesoporous TiO2 powders containing both anatase and rutile crystalline phases were produced. A challenging utilization of these porous MOF-derived Ti-based oxides is the optically-based quantitative detection of molecular oxygen (O-2) in gaseous and/or aqueous media. In this study, the photoluminescence (PL) intensity changes during O-2 exposure of two MOF-derived mixed-phase TiO2 powders were probed by exploiting the opposite response of rutile and anatase in VIS-PL and NIR-PL wavelength intervals. This result highlights promising future possibilities for the realization of MOF-derived doubly-parametric TiO2-based optical sensors.

30. Low Blue Dose Photodynamic Therapy with Porphyrin-Iron Oxide Nanoparticles Complexes: In Vitro Study on Human Melanoma Cells

Authors: Nistorescu, S; Udrea, AM; Badea, MA; Lungu, I; Boni, M; Tozar, T; Dumitrache, F; Maraloiu, VA; Popescu, RG; Fleaca, C; Andronescu, E; Dinischiotu, A; Staicu, A; Balas, M

Published: DEC 2021, PHARMACEUTICS, 13, DOI: 10.3390/pharmaceutics13122130

The purpose of this study was to investigate the effectiveness in photodynamic therapy of iron oxide nanoparticles (gamma-Fe2O3 NPs), synthesized by laser pyrolysis technique, functionalized with 5,10,15,20-(Tetra-4-sulfonatophenyl) porphyrin tetraammonium (TPPS) on human cutaneous melanoma cells, after only 1 min blue light exposure. The efficiency of porphyrin loading on the iron oxide nanocarriers was estimated by using absorption and FTIR spectroscopy. The singlet oxygen yield was determined via transient characteristics of singlet oxygen phosphorescence at 1270 nm both for porphyrin functionalized nanoparticles and rose bengal used as standard. The irradiation was performed with a LED (405 nm, 1 mW/cm(2)) for 1 min after melanoma cells were treated with TPPS functionalized iron oxide nanoparticles (gamma-Fe2O3 NPs_TPPS) and incubated for 24 h. Biological tests revealed a high anticancer effect of gamma-Fe2O3 NPs_TPPS complexes indi-cated by the inhibition of tumor cell proliferation, reduction of cell adhesion, and induction of cell death through ROS generated by TPPS under light exposure. The biological assays were combined with the pharmacokinetic prediction of the porphyrin.

31. 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.

32. 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)).

33. Electron paramagnetic resonance and microstructural insights into the thermal behavior of simonkolleite nanoplatelets

Authors: Rostas, AM; Kuncser, AC; Ghica, D; Palici, A; Maraloiu, VA; Vlaicu, ID

Published: MAY 7 2020, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 9512, DOI: 10.1039/d0cp00641f

The aim of this paper is the study of the thermal behavior of the simonkolleite Zn-5(OH)(8)Cl-2 center dot H2O (ZHC) by electron paramagnetic resonance (EPR) spectroscopy, in particular. It is well known that during heating ZHC undergoes a complex transformation which involves several overlapping stages. However, with reference to the data reported on this subject, it can be concluded that there is still an ongoing debate regarding the intermediate stages of this process. The data presented in this study support a simple decomposition process of the ZHC prepared using the precipitation method. The EPR data correlated to the data obtained by other experimental techniques, such as XRD, TEM, SEM and EDX, indicate that during the thermal treatment the ZHC suffers a partial decomposition to ZnO with no intermediate products. After annealing at 500 degrees C for 1 h, a recombination process of ZHC is observed. Moreover, the kinetics associated to these decomposition steps were determined and the evolution of the paramagnetic centers was also followed and studied. This study offers new information related to the thermal behavior of ZHC, especially regarding the EPR data which is reported for the first time on this subject and material.

34. 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.

35. Simple Ethanol Refluxing Method for Production of Blue-Colored Titanium Dioxide with Oxygen Vacancies and Visible Light-Driven Photocatalytic Properties

Authors: Lettieri, S; Gargiulo, V; Alfe, M; Amati, M; Zeller, P; Maraloiu, VA; Borbone, F; Pavone, M; Munoz-Garcia, AB; Maddalena, P

Published: FEB 13 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 3576, DOI: 10.1021/acs.jpcc.9b08993

We show that a simple ethanol (EtOH) refluxing treatment at mild temperature (120 degrees C) allows producing blue-colored and reduced titanium dioxide (TiO2-x) exhibiting improved visible-light (VIS) photocatalytic properties. The treatment causes an increase in the density of Ti(III) species and the appearance of two optical absorption features: a broad absorption band-responsible for the blue coloration- extending from the green region (similar to 2.3 eV) up to the near-infrared and a subgap absorption tail close to the band gap energy. The experimental results combined with a computation of the density of states via hybrid Hartree-Fock density functional support the hypothesis that the EtOH reflux treatment leads to formation of surface and subsurface oxygen (O) vacancies. We also show that the excitation-resolved photoluminescence technique allows a high-contrast detection of a subgap optical excitation band peaked at about 430 nm (similar to 2.9 eV), associated with anatase photoluminescence, whose intensity increases after the EtOH reflux treatment. This result gives a very direct support to the debated hypothesis identifying O vacancy states as the energy levels involved in the radiative transition of anatase TiO2. Improved photocatalytic degradation by the processed TiO2 under VIS illumination is demonstrated, and the possible mechanism involved in the formation of surface O vacancies is discussed. The method outlines a very simple, low-cost, and fast procedure to target the formation of O vacancies in the TiO2 surface region.

36. PHOTO-ELECTRICAL PROPERTIES OF THIN FILMS WITH GE NANOPARTICLES EMBEDDED IN TIO2 MATRIX

Authors: Stavarache, I; Maraloiu, VA

Published: 2019, ROMANIAN REPORTS IN PHYSICS, 71, DOI:

We present photo-electrical properties of thin films formed of Ge nanoparticles in TiO2 correlated with structure and morphology. The films co-deposited on Si using magnetron sputtering were annealed in conventional oven at 550 degrees C. We performed structure investigations by X-ray diffraction, transmission electron microscopy and measured current-voltage characteristics in dark and under illumination at different temperatures. We show that the films are formed of cubic Ge nanoparticles in nanostructured anatase TiO2 matrix. Also, (TiGe)O-2 with rutile structure was observed. The films have high photosensitivity under white light as the ratio between photo- and dark currents (-1 V) is of similar to 10(2).

37. 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.

38. Tailoring the Dopant Distribution in ZnO:Mn Nanocrystals

Authors: Ghica, D; Vlaicu, ID; Stefan, M; Maraloiu, VA; Joita, AC; Ghica, C

Published: MAY 3 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-43388-z

The synthesis of semiconductor nanocrystals with controlled doping is highly challenging, as often a significant part of the doping ions are found segregated at nanocrystals surface, even forming secondary phases, rather than incorporated in the core. We have investigated the dopant distribution dynamics under slight changes in the preparation procedure of nanocrystalline ZnO doped with manganese in low concentration by electron paramagnetic resonance spectroscopy, paying attention to the formation of transient secondary phases and their transformation into doped ZnO. The acidification of the starting solution in the co-precipitation synthesis from nitrate precursors lead to the decrease of the Mn2+ ions concentration in the core of the ZnO nanocrystals and their accumulation in minority phases, until similar to 79% of the Mn2+ ions were localized in a thin disordered shell of zinc hydroxynitrate (ZHN). A lower synthesis temperature resulted in polycrystalline Mn-doped ZHN. Under isochronal annealing up to 250 degrees C the bulk ZHN and the minority phases from the ZnO samples decomposed into ZnO. The Mn2+ ions distribution in the annealed nanocrystals was significantly altered, varying from a uniform volume distribution to a preferential localization in the outer layers of the nanocrystals. Our results provide a synthesis strategy for tailoring the dopant distribution in ZnO nanocrystals for applications ranging from surface based to ones involving core properties.

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. 3D hybrid structures based on biomimetic membranes and Caryophyllus aromaticus - "green" synthesized nano-silver with improved bioperformances

Authors: Barbinta-Patrascu, ME; Badea, N; Bacalum, M; Ungureanu, C; Suica-Bunghez, IR; Lordache, SM; Pirvu, C; Zgura, I; Maraloiu, VA

Published: AUG 2019, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 101, 137, DOI: 10.1016/j.msec.2019.03.069

The paper describes an innovative bio-design of some hybrid nanoarchitectures containing bioartificial membranes and silver nanoparticles phytogenerated by using a natural extract Caryophyllus aromaticus (cloves) that contains many bioactive compounds. Two kinds of liposomes with and without chlorophyll a (Chla) obtained through thin film hydration method were used to achieve bio-green-generated hybrids by a simple, cost effective bottom-up approach. The characteristic peaks of CE-nAg monitored by UV-Vis absorption have firstly demonstrated the biohybrids formation. The slightly blue shift and fluorescence quenching observed by fluorescence emission spectra highlighted the formation of hybrid systems by biointeraction between lipid vesicles and silver nanoparticles. The incorporation of silver nanoparticles in lipid vesicles resulted in significant changes of FT-IR spectra of liposomes, indicating a reorganization of biomimetic membranes. All the microscopic methods (SEM, AFM and TEM) confirmed the biosynthesis of "green" AgNPs together with associated biohybrids, their spherical and quasi-spherical shapes with nano-scaled size. By TEM assay it was shown that CE-nAg are surrounded by petal like cloud structures that consist of biopolymers like proteins or polysaccharides and other phytochemicals arising from clove extract. EDS spectra confirmed the formation of phyto-nanoAg and also the presence of silver in the biohybrids. In addition, Selected Area Electron Diffraction showed characteristic polycrystalline ring patterns for a cubic structure of the clove-generated AgNPs. The hybrid materials showed efficient physical stability, ie. xi value of - 28.0 mV (for biohybrids without Chla, BH) and of - 31.7 mV (for biohybrids labelled with Chla, Chla-BH), assured by strong electrostatic repulsive forces between particles. The "green" nano-silver particles (CE-nAg) showed remarkable antioxidant activity (AA = 90.2%). The biohybrids loaded with clove-AgNPs proved to be more effective, scavenging about 98.8% of free radicals (in case of ChlaBH), and of 92.6% (in case of BH). The antibacterial effectiveness showed that green AgNPs combine in a synergistic manner the antibacterial properties of clove extract with those of silver, resulting in an enhancement of inhibition diameter, by 20%. Chla-BH proved to be more potent against Escherichia coli, than BH, exhibiting an inhibition diameter of 42 mm. Regarding the in vitro cytotoxicity against tumour cells, the CE-nAg concentration significantly influenced the cell viability, ie. IC50 was 3.6% (v/v) for HT-29 cells. Chla-BH was more effective against HT-29 cancer cells at the concentrations ranging from 0 to 18% (v/v), when the normal cells were not affected. Clove-generated AgNPs exhibited haemolytic activity against hRBCs, while the biohybrids were haemocompatible. The action mechanism on the two cell lines (mouse fibroblast L929 cells and human colorectal adenocarcinoma HT-29 cells) investigated by fluorescence microscopy demonstrated that CE-nAg killed almost all the cells (94%) through necrosis at a concentration of 33.4% (v/v). The treatment of HT-29 cells with BH resulted in: 71.5% viable cells, 19.5% apoptotic and only 9% necrotic cells, while in the case of Chla-BH treatment, only 77.5% cells were viable, 16% cells were apoptotic and 6.5% were necrotic. In this way, the developed silver-based nanoparticles can represent viable promoters to develop new biohybrids with improved features, e.g. antioxidant and antibacterial effectiveness, haemolytic activity and greater specificity towards tumour cells.

41. Zinc incorporation in marine bivalve shells grown in mine-polluted seabed sediments: a case study in the Malfidano mining area (SW Sardinia, Italy)

Authors: Medas, D; Carlomagno, I; Meneghini, C; Aquilanti, G; Araki, T; Bedolla, DE; Buosi, C; Casu, MA; Gianoncelli, A; Kuncser, AC; Maraloiu, VA; De Giudici, G

Published: DEC 2018, ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH, 25, 36660, DOI: 10.1007/s11356-018-3504-y

Zinc incorporation into marine bivalve shells belonging to different genera (Donax, Glycymeris, Lentidium, and Chamelea) grown in mine-polluted seabed sediments (Zn up to 1% w/w) was investigated using x-ray diffraction (XRD), chemical analysis, soft x-ray microscopy combined with low-energy x-ray fluorescence (XRF) mapping, x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). These bivalves grew their shells, producing aragonite as the main biomineral and they were able to incorporate up to 2.0-80mg/kg of Zn, 5.4-60mg/kg of Fe and 0.5-4.5mg/kg of Mn. X-ray absorption near edge structure (XANES) analysis revealed that for all the investigated genera, Zn occurred as independent Zn mineral phases, i.e., it was not incorporated or adsorbed into the aragonitic lattice. Overall, our results indicated that Zn coordination environment depends on the amount of incorporated Zn. Zn phosphate was the most abundant species in Donax and Lentidium genera, whereas, Chamelea shells, characterized by the highest Zn concentrations, showed the prevalence of Zn-cysteine species (up to 56% of total speciation). Other Zn coordination species found in the investigated samples were Zn hydrate carbonate (hydrozincite) and Zn phosphate. On the basis of the coordination environments, it was deduced that bivalves have developed different biogeochemical mechanisms to regulate Zn content and its chemical speciation and that cysteine plays an important role as an active part of detoxification mechanism. This work represents a step forward for understanding bivalve biomineralization and its significance for environmental monitoring and paleoreconstruction.

42. Enhanced photoconductivity of SiGe-trilayer stack by retrenching annealing conditions

Authors: Sultan, MT; Gudmundsson, JT; Manolescu, A; Ciurea, ML; Palade, C; Maraloiu, AV; Svavarsson, HG

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 64, DOI:

We studied the effect of short term furnace annealing over the photoconductive properties of tristacked layer i.e. TiO2/(SiGe/TiO2)(3). The structure was prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A transmission electron microscopy and grazing incidence spectroscopy was used to analyze the morphology of the structure. Photoconductive properties were studied by measuring photocurrent spectra at different applied voltages and temperatures. Tristack layers were obtained with 5-10 nm SiGe nanocrystals (NCs) by annealing at 600 degrees C for 5 min. No sign of SiO2 formation was found inside stacked layers. A maximum in the photocurrent spectra was observed at 994 nm at 300 K but it red-shifted gradually to 1045 nm with decrease in temperature to 100 K. This transition in peak maxima is attributed to SiGe NCs, due to lattice vibration and to contribution of non-radiative recombination at low temperatures.

43. 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.

44. Heavy doping of ceria by wet impregnation: a viable alternative to bulk doping approaches

Authors: Florea, M; Avram, D; Maraloiu, VA; Cojocaru, B; Tiseanu, C

Published: OCT 7 2018, NANOSCALE, 10, 18054, DOI: 10.1039/c8nr03695k

To avoid the deleterious effects of dopant segregation, synthesis methods that facilitate a homogenous dopant distribution in the ceria lattice were employed. Though doping ceria by wet impregnation was also credited to induce a homogeneous solid solution even in the heavy regime (concentration >= 20%, A. Corma, P. Atienzar, H. Garcia and J. Chane-Ching, Nat. Mater., 2004, 3, 394-397), no follow up investigation has been reported. Herein, we investigated ceria nanoparticles (1% Tm-CeO2 and 1% Eu-CeO2) wetimpregnated with trivalent rare-earth (Yb, 20%), bivalent (Ca, 20%) and isovalent (Zr, 30%) metals, followed by annealing in air. Homogeneity of the solid solutions of Yb-impregnated ceria was confirmed by a two-feature characterization toolbox that included X-ray diffraction, Raman spectroscopy, transmission electron microscopy, as well as up-conversion emission as a probe tool. Since the up-conversion emission of Tm was not detectable in the absence of Yb while its efficiency depends on the average distance between Yb and Tm ions, the Yb incorporation and its migration from the surface to the lattice bulk sites in wet-impregnated ceria can be "visualized" and compared with that of the Yb bulk-doped counterpart. The use of Eu luminescence as a local probe confirmed the homogeneity of solid solutions of Ca and Zr-impregnated ceria and also sustained the opposite roles of Ca and Zr as the repeller and the scavenger of oxygen vacancies, respectively. All these results suggested that heavy doping of ceria by wet impregnation with metals with +2, +3 and +4 valencies represent a facile alternative to conventional doping approaches. Therefore, the effects of the amount and the type of metal dopant on the structural properties of CeO2 could be investigated in a more systematic and probably a more reproducible manner, which would significantly increase the potential of ceria in catalysis and other applications.

45. Optoelectric charging-discharging of Ge nanocrystals in floating gate memory

Authors: Palade, C; Slav, A; Lepadatu, AM; Maraloiu, AV; Dascalescu, I; Iftimie, S; Lazanu, S; Ciurea, ML; Stoica, T

Published: NOV 19 2018, APPLIED PHYSICS LETTERS, 113, DOI: 10.1063/1.5039554

Photo-induced effects on charging and discharging of nanocrystals (NCs) in capacitor memories with Ge NCs in an HfO2 matrix as a floating gate layer are studied. The sequence of layers HfO2/Ge-HfO2/ HfO2 was deposited on a p-Si substrate using magnetron sputtering. Well separated Ge NCs are obtained after rapid thermal annealing at 600 degrees C. The optoelectric capacitor memories were fabricated with a semi-transparent electrode on top of the structure and an Al electrode on the back side of the Si substrate. Light illumination effects on hysteresis curves were investigated using different operation modes. The hysteresis window increases by increasing the light exposure time. The spectral dependence of the hysteresis window shows the maximum contribution of the light in the wavelength range of 950-1000 nm, corresponding to both contributions from the Si substrate and from Ge NCs. The stored information about the electrical and optical pulses is also investigated in the regime of the flat band potential measurements (retention measurements). It is shown that in our memory structure, the photo-effect on the memory retention corresponds to a tunnelling transfer of negative charges from the Si substrate to Ge NCs, up to a mean value of 1.6 electrons per NC. Published by AIP Publishing.

46. Limits and Particularities of the Synthesis of Ba1-xCaxTiO3 for Piezoelectric Applications, by Topochemical Conversion from Molten Salt Solutions

Authors: Vlaicu, ID; Maraloiu, AV; Ghica, D; Mercioniu, IF; Stefan, M; Vlaicu, AM; Negrea, RF; Kuncser, AC; Bulat, S; Krzmanc, MM; Ciobanu, R; Plopa, O

Published: 2018, 2018 INTERNATIONAL CONFERENCE AND EXPOSITION ON ELECTRICAL AND POWER ENGINEERING (EPE), 1050, DOI:

Because of the unique properties of the ferroelectric perovskite particles with a well-defined anisotropic form like shape-and size dependent at low dimensions they have all the attention of the scientific world. Extensive morphostructural techniques will be used to characterize the piezoelectric material.

47. Development and Biocompatibility Evaluation of Photocatalytic TiO2/Reduced Graphene Oxide-Based Nanoparticles Designed for Self-Cleaning Purposes

Authors: Nica, IC; Stan, MS; Popa, M; Chifiriuc, MC; Pircalabioru, GG; Lazar, V; Dumitrescu, I; Diamandescu, L; Feder, M; Baibarac, M; Cernea, M; Maraloiu, VA; Popescu, T; Dinischiotu, A

Published: SEP 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7090279

Graphene is widely used in nanotechnologies to amplify the photocatalytic activity of TiO2, but the development of TiO2/graphene composites imposes the assessment of their risk to human and environmental health. Therefore, reduced graphene oxide was decorated with two types of TiO2 particles co-doped with 1% iron and nitrogen, one of them being obtained by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution, and the other one after a sequential precipitation of these two cations for a higher concentration of iron on the surface. Physico-chemical characterization, photocatalytic efficiency evaluation, antimicrobial analysis and biocompatibility assessment were performed for these TiO2-based composites. The best photocatalytic efficiency was found for the sample with iron atoms localized at the sample surface. A very good anti-inhibitory activity was obtained for both samples against biofilms of Gram-positive and Gram-negative strains. Exposure of human skin and lung fibroblasts to photocatalysts did not significantly affect cell viability, but analysis of oxidative stress showed increased levels of carbonyl groups and advanced oxidation protein products for both cell lines after 48 h of incubation. Our findings are of major importance by providing useful knowledge for future photocatalytic self-cleaning and biomedical applications of graphene-based materials.

48. 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.

49. Electrochemically shape-controlled transformation of magnetron sputtered platinum films into platinum nanostructures enclosed by high-index facets

Authors: Khalakhan, I; Lavkova, J; Matolinova, I; Vorokhta, M; Potin, V; Kus, P; Vaclavu, M; Maraloiu, VA; Kuncser, AC; Matolin, V

Published: JAN 15 2017, SURFACE & COATINGS TECHNOLOGY, 309, 11, DOI: 10.1016/j.surfcoat.2016.11.017

A new method based on transformation of magnetron sputtered platinum thin films into platinum nanostructures enclosed by high-index facets, using electrochemical potential cycling in a twin working electrode system is reported. The controllable formation of various Pt nanostructures, described in this paper, indicates that this method can be used to control a selective growth of high purity Pt nanostructures with specific shapes (facets or edges). The method opens up new possibilities for electrochemical preparation of nanostructured Pt catalysts at high yield. (C) 2016 Elsevier B.V. All rights reserved.

50. Photo-sensitive Ge nanocrystal based films controlled by substrate deposition temperature

Authors: Stavarache, I; Maraloiu, VA; Negrila, C; Prepelita, P; Gruia, I; Iordache, G

Published: OCT 2017, SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 32, DOI: 10.1088/1361-6641/aa8154

Lowering the temperature of crystallization by deposition of thin films on a heated substrate represents the easiest way to find new means to develop and improve new working devices based on nanocrystals embedded in thin films. The improvements are strongly related with the increasing of operation speed, substantially decreasing the energy consumption and reducing unit fabrication costs of the respective semiconductor devices. This approach avoids major problems, such as those related to diffusion or difficulties in controlling nanocrystallites size, which appear during thermal treatments at high temperatures after deposition. This article reports on a significant progress given by structuring Ge nanocrystals (Ge-NCs) embedded in silicon dioxide (SiO2) thin films by heating the substrate at 400 degrees C during co-deposition of Ge and SiO2 by magnetron sputtering. As a proof-of-concept, a Si/Ge-NCs:SiO2 photo-sensitive structure was fabricated thereof and characterized. The structure shows superior performance on broad operation bandwidth from visible to near-infrared, as strong rectification properties in dark, significant current rise in the inversion mode when illuminated, high responsivity, high photo-detectivity of 10(14) Jones, quick response and significant conversion efficiency with peak value reaching 850% at -1 V and about 1000 nm. This simple preparation approach brings an important contribution to the effort of structuring Ge nanocrystallites in SiO2 thin films at a lower temperature for the purpose of using these materials for devices in optoelectronics, solar cells and electronics on flexible substrates.

51. Mn2+ ions distribution in doped sol-gel deposited ZnO films

Authors: Stefan, M; Ghica, D; Nistor, SV; Maraloiu, AV; Plugaru, R

Published: FEB 28 2017, APPLIED SURFACE SCIENCE, 396, 1889, DOI: 10.1016/j.apsusc.2016.02.167

The localization and distribution of the Mn2+ ions in two sol-gel deposited ZnO films doped with different manganese concentrations were investigated by electron paramagnetic resonance spectroscopy and analytical transmission electron microscopy. In the lightly doped sample the Mn2+ ions are mainly localized substitutionally at isolated tetrahedrally coordinated Zn2+ sites in both crystalline ZnO nanograins (34%) and surrounding disordered ZnO (52%). In the highly doped ZnO film, a much smaller proportion of manganese substitutes Zn2+ in the crystalline and disordered ZnO (10%). The main amount (85%) of manganese aggregates in a secondary phase as an insular-like distribution between the ZnO nanograins. The remaining Mn2+ ions (14% and 5% at low and high doping levels, respectively) are localized at isolated, six-fold coordinated sites, very likely in the disordered intergrain region. Annealing at 600 degrees C induced changes in the Mn2+ ions distribution, reflecting the increase of the ZnO crystallization degree, better observed in the lightly doped sample. (C) 2016 Elsevier B.V. All rights reserved.

52. Submicrometer Hollow Bioglass Cones Deposited by Radio Frequency Magnetron Sputtering: Formation Mechanism, Properties, and Prospective Biomedical Applications

Authors: Popa, AC; Stan, GE; Besleaga, C; Ion, L; Maraloiu, VA; Tulyaganov, DU; Ferreira, JMF

Published: FEB 24 2016, ACS APPLIED MATERIALS & INTERFACES, 8, 4367, DOI: 10.1021/acsami.6b00606

This work reports on the unprecedented magnetron sputtering deposition of submicrometric hollow cones of bioactive glass at low temperature in the absence of any template or catalyst. The influence of sputtering conditions on the formation and development of bioglass cones was studied. It was shown that larger populations of well-developed cones could be achieved by increasing the argon sputtering pressure. A mechanism describing the growth of bioglass hollow cones is presented, offering the links for process control and reproducibility of the cone features. The composition, structure, and morphology of the as-synthesized hollow cones were investigated by energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), grazing incidence geometry X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)-selected area electron diffraction (SAED). The in vitro biological performance, assessed by degradation tests (ISO 10993-14) and cytocompatibility assays (ISO 10993-5) in endothelial cell cultures, was excellent. This allied with resorbability and the unique morphological features make the submicrometer hollow cones interesting candidate material devices for focal transitory permeabilization of the blood brain barrier in the treatment of carcinoma and neurodegenerative disorders.

53. Ferritin surplus in mouse spleen 14 months after intravenous injection of iron oxide nanoparticles at clinical dose

Authors: Tamion, A; Hillenkamp, M; Hillion, A; Maraloiu, VA; Vlaicu, ID; Stefan, M; Ghica, D; Rositi, H; Chauveau, F; Blanchin, MG; Wiart, M; Dupuis, V

Published: AUG 2016, NANO RESEARCH, 9, 2410, DOI: 10.1007/s12274-016-1126-6

In this study, we followed the biodegradation of ultra-small superparamagnetic iron oxide nanoparticles injected intravenously at clinical doses in mice. An advanced fitting procedure for magnetic susceptibility curves and low-temperature hysteresis loops was used to fully characterize the magnetic size distribution as well as the magnetic anisotropy energy of the injected P904 nanoparticles (Guerbet Laboratory). Additional magnetometry measurements and transmission electronic microscopy observations were systematically performed to examine dehydrated samples from the spleen and liver of healthy C57B16 mice after nanoparticle injection, with sacrifice of the mice for up to 14 months. At 3 months after injection, the magnetic properties of the spleen and liver were dramatically different. While the liver showed no magnetic signals other than those also present in the reference species, the spleen showed an increased magnetic signal attributed to ferritin. This surplus of ferritin remained constant up to 14 months after injection.

54. 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.

55. 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.

56. Nanostructured germanium deposited on heated substrates with enhanced photoelectric properties

Authors: Stavarache, I; Maraloiu, VA; Prepelita, P; Iordache, G

Published: OCT 21 2016, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 7, 1500, DOI: 10.3762/bjnano.7.142

Obtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high Ge content (50 %) into SiO2. Crystalline Ge nanoparticles were directly formed during co-deposition of SiO2 and Ge on substrates at 300, 400 and 500 degrees C. Using this approach, effects related to Ge-Ge spacing are emphasized through a significant improvement of the spatial distribution of the Ge nanoparticles and by avoiding multi-step fabrication processes or Ge loss. The influence of the preparation conditions on structural, electrical and optical properties of the fabricated nanostructures was studied by X-ray diffraction, transmission electron microscopy, electrical measurements in dark or under illumination and response time investigations. Finally, we demonstrate the feasibility of the procedure by the means of an Al/n-Si/Ge:SiO2/ITO photodetector test structure. The structures, investigated at room temperature, show superior performance, high photoresponse gain, high responsivity (about 7 AW(-1)), fast response time (0.5 mu s at 4 kHz) and great optoelectronic conversion efficiency of 900% in a wide operation bandwidth, from 450 to 1300 nm. The obtained photoresponse gain and the spectral width are attributed mainly to the high Ge content packed into a SiO2 matrix showing the direct connection between synthesis and optical properties of the tested nanostructures. Our deposition approach put in evidence the great potential of Ge nanoparticles embedded in a SiO2 matrix for hybrid integration, as they may be employed in structures and devices individually or with other materials, hence the possibility of fabricating various heterojunctions on Si, glass or flexible substrates for future development of Si-based integrated optoelectronics.

57. 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.

58. 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.

59. 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.

60. 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.

61. 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.

62. Pattern formation on silicon by laser-initiated liquid-assisted colloidal lithography

Authors: Ulmeanu, M; Petkov, P; Ursescu, D; Maraloiu, VA; Jipa, F; Brousseau, E; Ashfold, MNR

Published: NOV 13 2015, NANOTECHNOLOGY, 26, DOI: 10.1088/0957-4484/26/45/455303

We report sub-diffraction limited patterning of Si substrate surfaces by laser-initiated liquid-assisted colloidal lithography. The technique involves exposing a two-dimensional lattice of transparent colloidal particles spin coated on the substrate of interest (here Si) immersed in a liquid (e.g. methanol, acetone, carbon tetrachloride, toluene) to a single picosecond pulse of ultraviolet laser radiation. Surface patterns formed using colloidal particles with different radii in the range 195 nm <= R <= 1.5 mu m and liquids with differing indices of refraction (n(liquid)) are demonstrated, the detailed topographies of which are sensitively dependent upon whether the index of refraction of the colloidal particle (n(colloid)) is greater or smaller than n(liquid) (i.e. upon whether the incident light converges or diverges upon interaction with the particle). The spatial intensity modulation formed by diffraction of the single laser pulse by the colloidal particles is imprinted into the Si substrate.

63. 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.

64. 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.

65. 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.

66. 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.

67. 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.

68. From synthetic to natural nanoparticles: monitoring the biodegradation of SPIO (P904) into ferritin by electron microscopy

Authors: Lopez-Castro, JD; Maraloiu, AV; Delgado, JJ; Calvino, JJ; Blanchin, MG; Galvez, N; Dominguez-Vera, JM

Published: 2011, NANOSCALE, 3, 4599, DOI: 10.1039/c1nr10980d

A strong focus on Superparamagnetic Iron Oxide Nanoparticles (SPIOs) has been appreciated recently especially for their use in Magnetic Resonance Imaging (MRI). However, some questions are being raised over these particles due to their long-term toxicity related to the production of toxic free iron during their biodegradation. Here we show by Electron Microscopy how SPIOs (P904) (Guerbet, Paris) are degraded after they are taken up by macrophages, so that iron from the SPIO core is progressively incorporated into the iron-storing protein ferritin (a nontoxic form of iron).

69. 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.

70. 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.

71. Study of magnetic nanovectors by Wet-STEM, a new ESEM mode in transmission

Authors: Maraloiu, VA; Hamoudeh, M; Fessi, H; Blanchin, MG

Published: DEC 15 2010, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 352, 392, DOI: 10.1016/j.jcis.2010.08.066

Many nanovectors used for therapy (drug targeting radiation therapy) or diagnostic such as Magnetic Resonance Imaging (MRI) have a composite structure consisting of an organic core or organic coverage encapsulating magnetic nanoparticles and they are commonly dispersed in liquid suspensions for intravenous injection Here is presented the application of a new Environmental Scanning Electron Microscopy (ESEM) mode in transmission so called Wet-STEM for transmission imaging of droplets of such suspensions This is illustrated by Wet-STEM images from PLLA/Re nanospheres (about 100-300 nm in diameter) loaded with magnetite nanoparticles (about 10 nm in diameter) and from iron oxide core (about 5 nm in size) MRI contrast agents both examples in aqueous suspensions It is shown that the Wet STEM mode allows both the collective behavior of such nanovectors in suspension to be characterized and the inner composite structure of individual vectors to be revealed Such experimental results are discussed by comparison with Monte Carlo computer simulations of the distribution of the electrons scattered through the samples in rather large solid angles (between 20 degrees and 47 degrees) corresponding to the detection conditions (C) 2010 Elsevier Inc All rights reserved

72. 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.

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