NIMP| Catalin NEGRILA, Author at NIMP

Resume

Constantin Cătălin Negrilă, II degree Scientific Researcher in INCDFM, born on 16.08.1978, graduate of the University of Bucharest, Faculty of Physics, PhD in 2011 at the University of Bucharest, Faculty of Physics, completed a work stage (training in XPS technique ) at the Institut für Angewandte Chemie Berlin-Adlershof during August-September 2004.

Areas of interest / expertise: Surface and interface analysis techniques (XPS, AES, UPS, STM, SHG, CRDS), Semiconductor physics and technology (techniques for growing and obtaining semiconductor single crystals, techniques for obtaining of thin semiconductor films, semiconductor interfaces, optical and electrical characterization methods, active structures and semiconductor devices, heterostructures, vacuum and vacuum systems technology, data acquisition and computer programming.

More than 120 papers in ISI indexed journals - J Cryst Growth, Appl Surf Sci, Coatings, Polymers, Nanomater, Electrochim Acta, Catal Today, Phys Chem Chem Phys, J of Nanomater. 1088 citations, Hirsch Index 21.

Member in Editorial Board of Materials (since 2021). Reviewer to Surf Interfaces, J of Nanomater, J of Optelectron Adv Mater.

Project manger of a Post Doc type project : PD- PN-II-RU-PD-2012-3-0051, Improving of some in situ techniques for the obtaining of metal/GaAs structures with applications in X-Ray detection. Contract no. 20-26.04.2013- 300000 lei.

Responsible for more research topics within the Core Projects. 8 patents published, awarded at ProInvent 2009, ProInvent2013 and Geneva 2012 exhibitions.

Contracts with companies worth more than 70000 lei.

UEF-ID Brainmap: U-1700-039K-8673

ORCID: 0000-0002-5756-2851

Web of Science ResearcherID: B-9285-2012

Publications

1. Sodium bicarbonate-hydroxyapatite used for removal of lead ions from aqueous solution

Authors: Predoi, SA; Ciobanu, SC; Chifiriuc, CM; Iconaru, SL; Predoi, D; Negrila, CC; Marinas, IC; Raaen, S; Rokosz, K; Motelica-Heino, M

Published: JAN 1 2024, CERAMICS INTERNATIONAL, 50, DOI: 10.1016/j.ceramint.2023.10.273

This study reports the development of a novel biocomposite for potential applications in the environmental remediation. The hydroxyapatite/sodium bicarbonate (HAp-SB) biocomposite obtained by a cheap method could offer promising characteristics to be used in environmental applications. The obtaining of HAp-SB ceramic composites was studied with the aim of increasing the adsorption efficiency of lead ions from contaminated waters. A composite material (HAp-SB) with good crystallinity that preserves the hexagonal structure of pure hydroxyapatite was obtained. For the powder recovered after decontamination of the lead solution (PbHAp-SB), the XRD model highlighted additional maxima belonging to Ca10(PO4)5(OH)2, Ca0.805Pb4.195(PO4)(OH) and PbH2P2O7. The FTIR spectra of PbHAp-SB are similar to those of HAp-SB composites showing a broadening of the vibration peaks and a slight shift. The XPS and EDS studies illustrated the purity of the HAp-SB sample. Moreover, the presence of lead in the powder recovered after decontamination was also highlighted by XPS and EDS studies. The efficiency of HAp-SB in the adsorption of Pb2+ ions from the contaminated solution was also highlighted by ultrasound studies using double-distilled water as the reference liquid. The adsorption kinetics were investigated with the aid of Langmuir and Freundlich theoretical models. The results demonstrated that the HAp-SB ceramic composite has a strong affinity for the adsorption of Pb2+ ions from contaminated solutions. The removal efficiency of Pb2+ ions was about 92% for the initial Pb2+ concentration above 50 mg/L. The results of the cell viability and cytotoxicity studies demonstrated that HAp-SB nanoparticles did not influence negatively the HeLa cell's viability and did not induce any significant changes of the morphological features of HeLa cells after 24 h of incubation. The batch adsorption results as well as the cytotoxicity assay results suggested that the HAp-SB powder could be successfully used for the removal of Pb2+ from contaminated water.

2. Iron oxide/hydroxide-nitrogen doped graphene-like visible-light active photocatalytic layers for antibiotics removal from wastewater

Authors: Ivan, R; Popescu, C; Antohe, VA; Antohe, S; Negrila, C; Logofatu, C; del Pino, AP; György, E

Published: FEB 15 2023, SCIENTIFIC REPORTS, 13, 2740, DOI: 10.1038/s41598-023-29927-9

Hybrid layers consisting of Fe oxide, Fe hydroxide, and nitrogen doped graphene-like platelets have been synthesized by an eco-friendly laser-based method for photocatalytic applications. The complex composite layers show high photodecomposition efficiency towards degradation of antibiotic molecules under visible light irradiation. The photodecomposition efficiency was investigated as a function of relative concentrations of base materials, Fe oxide nanoparticles and graphene oxide platelets used for the preparation of target dispersions submitted to laser irradiation. Although reference pure Fe oxide/Fe hydroxide layers have high absorption in the visible spectral region, their photodecomposition efficiency is negligible under the same irradiation conditions. The high photocatalytic decomposition efficiency of the nanohybrid layer, up to 80% of the initial antibiotic molecules was assigned to synergistic effects between the constituent materials, efficient separation of the electron-hole pairs generated by visible light irradiation on the surface of Fe oxide and Fe hydroxide nanoparticles, in the presence of conducting graphene-like platelets. Nitrogen doped graphene-like platelets contribute also to the generation of electron-hole pairs under visible light irradiation, as demonstrated by the photocatalytic activity of pure, reference nitrogen doped graphene-like layers. The results also showed that adsorption processes do not contribute significantly to the removal of antibiotic molecules from the test solutions. The decrease of the antibiotic concentration under visible light irradiation was assigned primarily to photocatalytic decomposition mechanisms.

3. Boron and nitrogen co-doped carbon-based nanomaterials/nickel oxide/ hydroxide hybrids for sunlight induced photocatalytic water cleaning

Authors: Lebière, PG; Ivan, R; del Pino, AP; Logofatu, C; Negrila, C; György, E

Published: NOV 5 2023, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 676, 132159, DOI: 10.1016/j.colsurfa.2023.132159

B doped as well as B and N co-doped highly reduced graphene oxide and multiwall carbon nanotubes/Ni oxide and Ni hydroxide nanohybrid layers were synthesized using a one-step laser technique. NiO nanoparticles, graphene oxide platelets, and multiwall carbon nanotubes were used as starting materials for the preparation of the composite layers. H3BO3 was used as B precursor and urea as well as NH3 as N precursors for B and N co -doping of the composite layers. The influence of the nature and concentration of the B and N precursors on the physico-chemical properties of the nanohybrid layers, chemical composition and chemical bonding states, crystalline structure, as well as charge transfer properties was systematically investigated. The relation between the physico-chemical properties and functional characteristics of the nanohybrid layers, photocatalytic removal of water contaminants under simulated sun irradiation conditions was studied, identifying the optimum con-centrations of the dopant precursor materials. The mechanism of the photodegradation process was explored, based of the band structure of the composites. The main intermediates, reactive oxygen species implied in the photocatalytic degradation processes of organic molecules, was investigated through the addition of scavengers to the organic dye test solutions. The highest photocatalytic activities were achieved for B and N co-doped samples synthesised using H3BO3 as B and urea as N precursors.

4. Photocatalytic Activity of the Blends Based on TiO2 Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

The aim of this work is to highlight the influence of blends based on TiO2 nanoparticles and reduced graphene oxide (RGO) on the photodegradation of acetaminophen (AC). To this end, the catalysts of TiO2/RGO blends with RGO sheet concentrations equal 5, 10, and 20 wt. % were prepared by the solid-state interaction of the two constituents. The preferential adsorption of TiO2 particles onto the RGO sheets' surfaces via the water molecules on the TiO2 particle surface was demonstrated by FTIR spectroscopy. This adsorption process induced an increase in the disordered state of the RGO sheets in the presence of the TiO2 particles, as highlighted by Raman scattering and scanning electron microscopy (SEM). The novelty of this work lies in the demonstration that TiO2/RGO mixtures, obtained by the solid-phase interaction of the two constituents, allow an acetaminophen removal of up to 95.18% after 100 min of UV irradiation. This TiO2/RGO catalyst induced a higher photodegradation efficiency of AC than TiO2 due to the presence of RGO sheets, which acted as a capture agent for the photogenerated electrons of TiO2, hindering the electron-hole recombination. The reaction kinetics of AC aqueous solutions containing TiO2/RGO blends followed a complex first-order kinetic model. Another novelty of this work is the demonstration of the ability of PVC membranes modified with Au nanoparticles to act both as filters for the removal of TiO2/RGO blends after AC photodegradation and as potential SERS supports, which illustrate the vibrational properties of the reused catalyst. The reuse of the TiO2/RGO blends after the first cycle of AC photodegradation indicated their suitable stability during the five cycles of pharmaceutical compound photodegradation.

5. Defect structures and (ferro)magnetism in Zn_1-xFe_xO nanoparticles with the iron concentration level in the dilute regime (x = 0.001 - 0.01) prepared from acetate precursors

Authors: Mihalache, V; Negrila, C; Secu, M; Mercioniu, I; Iacob, N; Kuncser, V

Published: AUG 2023, RESULTS IN PHYSICS, 51, 106644, DOI: 10.1016/j.rinp.2023.106644

Zn1-xFexO nanoparticles with the iron concentrations level in the dilute regime (x = 0.001---0.01) were produced by a sol-gel route from acetate precursors along with an un-doped and 3 at.% Fe-doped reference. The X-ray diffraction of the un-doped and 0.1-1 at.% Fe-doped samples reveal the reflections for only the ZnO wurtzite structure. Fe doping enhances the a-axis lattice constant, the unit cell volume and the microstrain. Iron doping reduces the average crystallite/particle size (confirmed by Scanning Electron Microscopy), improving the surface-to-volume ratio or the concentration of defective surface sites. XPS identifies the iron in both Fe3+ and Fe2+ states. XPS and Fe-57 Mossbauer spectroscopy indicate a broad distribution (distortion) of Fe3+ sites on the surface of ZnO nanoparticles. The blue shift and broadening of the UV emission, and quenching of defect-related photoluminescence in the Fe-doped samples verify the presence of iron in the ZnO lattice and surface intrinsic defects. 0.1-1 at.% Fe-doped ZnO show room temperature ferromagnetism, RTFM, characteristic of dilute magnetic semiconductors, DMS. The magnetization measurements with temperature evidence an antiferromagnetic alignment and an increase of ferromagnetic contribution with Fe doping up to 1 at.%. Zn0.97Fe0.3O reference is a superparamagnetic ZnO/ZnFe2O4 nanocomposite with a blocking temperature of 20 K; HRTEM shows (ultra)fine ZnFe2O4 particles at the surface of ZnO nanoparticles. The analysis of experimental data of 0.1-1 at.% Fe-doped ZnO was done in terms of iron coupling with intrinsic defects, which can generate surface Fe3+ states with geometries similar to the Fe3+ in inverse spinel ZnFe2O4. The superexchange interaction (resembling that in the inverse spinel ZnFe2O4) between the Fe3+ sites with distorted configuration resulting in ferrimagnetism was hypothesised as a possible mechanism of RTFM. Experimental (structural, local chemical, magnetic, optical) and interpretation results can be used to optimize the processing conditions for Fe-doped ZnO to serve as an effective DMS, e.g. for spintronic applications.

6. Photocatalytic Activity of the Blends Based on TiO₂ Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

7. Pulsed laser deposited V2O3 thin-films on graphene/aluminum foil for micro-battery applications

Authors: Tite, T; Ungureanu, C; Buga, M; Stavarache, I; Matei, E; Negrila, CC; Trupina, L; Spinu-Zaulet, A; Galca, AC

Published: MAR 15 2023, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 933, 117290, DOI: 10.1016/j.jelechem.2023.117290

The development of new thin-film cathodes triggered a recent research interest in energy storage applications. Over the past years, vanadium oxides have been extensively explored as promising electrodes for batteries owing to their rich valence states and remarkable electrochemical properties. Herein, we report on the synthe-sis of undoped and Sn doped V2O3 thin-films on graphene (G)/Al foil by pulsed laser deposition followed by rapid thermal annealing in N2 at low temperature (similar to 430 degrees C). The obtaining V2O3 phase on graphene/Al foil (G/Al) has been confirmed by X-ray diffraction and Raman and X-ray photoelectron spectroscopy analyses. The synthesized vanadium oxide films were tested as cathodes in coin cells. The electrochemical properties have been systematically investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) measurements. A superior electrochemical performance was observed for the V2O3 on G/Al structures, with an initial capacity of around 300 mAh g-1, with respect to the bare G/Al electrode. The use of the Sn-doped (5 mol%) V2O3 thin-films improved slightly the initial capac-ity up to a value of ca. 311 mAh g-1. Both V2O3/G/Al and Sn-doped V2O3/G/Al exhibited excellent cycling performances after 40 cycles with a capacity maintenance at a C-rate C/20 of 317 mAh g-1. Long-term cycling test (up to 200 cycles) showed that the Sn doping could be an excellent strategy to improve the stability of the electrodes, which yielded a capacity loss of only 0.128% per cycle. Possible mechanisms are presented and dis-cussed. This work could serve as point of reference for future developments in the field of batteries employing vanadium oxide-based thin-films deposited by physical vapor deposition techniques.

8. WO₃ layer sensitized with BiVO₄ and MIL-101(Fe) as photoanode for photoelectrochemical water oxidation

Authors: Sima, M; Vasile, E; Preda, N; Matei, E; Sima, A; Negrila, C

Published: OCT 2023, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 181, 111472, DOI: 10.1016/j.jpcs.2023.111472

Thick tungsten oxide layers were prepared electrophoretically in order to be used as photoanodes in photoelectrochemical water oxidation applications. The highest photocurrent density was obtained for a WO3 layer with thickness of similar to 900 nm. Additionally, WO3/BiVO4 and WO3/BiVO4/MIL-101(Fe) heterojunctions have been fabricated using WO3 layer as substrate. WO3/BiVO4 shows an increased value of the electrochemical active surface area indicating that more sites of this photoanode are activated through the formation of the heterojunction. The small V5+ signals observed in the V 2p XPS spectra of these heterojunctions were attributed to the substitution of V5+ atoms with W6+ atoms on the surface of BiVO4. Excessive W doping of the BiVO4 film determined the decrease of the photoelectrochemical performance of WO3/BiVO4 photoanode. The significant improvement of the photoconversion efficiency of the sample decorated with MIL-101(Fe) indicated that this cocatalyst provides sites more efficiently in the photoelectrochemical process. This performance was correlated with the reduced value of the charge transfer resistance at electrode/electrolyte interface obtained from electrochemical impedance spectroscopy investigation.

9. 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.

10. Boron and nitrogen co-doped carbon-based nanomaterials/nickel oxide/hydroxide hybrids for sunlight induced photocatalytic water cleaning

Authors: Lebière, PG; Ivan, R; del Pino, AP; Logofatu, C; Negrila, C; György, E

Published: NOV 5 2023, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 676, 132159, DOI: 10.1016/j.colsurfa.2023.132159

11.
Ageing studies of Multi-Strip Multi-Gap Resistive Plate Counters based on low resistivity glass electrodes in high irradiation dose & nbsp;

Authors: Bartos, D; Burducea, C; Burducea, I; Caragheorgheopol, G; Constantin, F; Craciun, L; Dorobantu, D; Ghena, M; Iancu, D; Marcu, A; Mateescu, G; Mereuta, P; Moise, V; Negrila, C; Negut, D; Petris, M; Petrovici, M; Radulescu, L; Aprodu, V; Prodan, L; Radu, A; Stoian, G

Published: FEB 1 2022, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1024, DOI: 10.1016/j.nima.2021.166122

Detailed tests and analysis of ageing effects of high irradiation dose on Multi-Strip Multi-Gap Resistive Plate Counters (MSMGRPC) based on low resistivity glass electrodes, foreseen to be used for the most forward polar angles covered by the Time-of Flight (ToF) sub-detector of the Compressed Baryonic Matter (CBM) experiment at Facility for Antiprotons and Ion Research (FAIR) - Darmstadt are reported. The tests were performed at a multi-purpose irradiation facility of IFIN-HH based on( 60)Co source. MSMGRPC efficiency, cluster size, surface and volume resistivity of the glass electrodes after irradiation are measured and compared with their values before irradiation. The results of a comprehensive analysis of the composition and properties of the deposited layers on the glass electrodes, based on different methods, i.e. Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), foil Elastic Recoil Detection Analysis (ERDA), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Terahertz Time Domain Spectroscopy (THz-TDS), are presented.

12. 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.

13. The Photoluminescence and Vibrational Properties of Black Phosphorous Sheets Chemically/Electrochemically Functionalized in the Presence of Diphenylamine

Authors: Baibarac, M., Burlanescu, T., Stroe, M., Smaranda, I., & Negrila, C.

Published: NOV 2022, Polymers, 21, 4479, DOI: 10.3390/polym14214479

In this work, new information concerning the optical properties of black phosphorus (BP) sheets chemically/electrochemically functionalized with diphenyl amine (DPA) and its macromolecular compound (poly(diphenylamine) (PDPA)) in the absence/presence of phosphotungstic acid (PTA) is reported. Raman scattering and FTIR spectroscopy studies indicate that the interaction of BP with PTA leads to the elimination of the PxOy layer onto the surface of the BP sheets. In the case of the chemical interaction of BP with DPA, the reaction product corresponds to DPA chemically functionalized BP sheets having an imino-phosphorane (IP) structure. The electrochemical oxidation of BP sheets chemically functionalized with DPA in the presence of PTA leads to an increase in the weight of P-N bonds as a consequence of the generation of PDPA doped with the PTA heteropolyanions, as shown by FTIR spectroscopy and Raman scattering. This process is evidenced by a shift of the Raman line from 362 cm(-1) to 378 cm(-1), assigned to the A(1g) mode. This change was explained by taking into account the compression of the layers containing P atoms, which is induced by PDPA macromolecular chains. The decrease in the intensity of the PL spectra of DPA as well as PDPA, in the presence of BP, indicates that BP acts as a PL quenching agent for these compounds. A preferential orientation of the PDPA doped with the PTA heteropolyanions on the surface of BP sheets is highlighted by the variation of the binding angle of the PDPA on the surface of BP sheets from 44.7 degrees to 39.9 degrees.

14. Bulk and surface characteristics of co-electrodeposited Cu2FeSnS4 thin films sulfurized at different annealing temperatures

Authors: El Khouja, O; Negrila, CC; Nouneh, K; Secu, M; Touhami, ME; Matei, E; Stancu, V; Enculescu, M; Kuncser, V; Galca, AC

Published: JUN 15 2022, JOURNAL OF ALLOYS AND COMPOUNDS, 906, 164379, DOI: 10.1016/j.jallcom.2022.164379

In this study, stannite, Cu2FeSnS4 (CFTS), absorber films were obtained by electrodeposition on Molybdenum-coated soda-lime substrates, followed by sulfurization treatment at certain temperatures in the 400-550 degrees C range. The purposes of this work were to control the manufacturing of CFTS films with good stoichiometry, high crystallinity and to study the annealing temperature impact on CFTS films properties. The X-ray diffraction and the Raman spectroscopy measurement distinguished the CFTS phase formation, with a presence of SnS2 secondary phase. The energy dispersive spectroscopy results reveal compositional differences between samples as well as the in-depth gradients. The photoluminescence emission band around 1.35-1.40 eV is slightly below the direct bandgap inferred from the conventional spectroscopy (diffuse reflectance). X-ray photoelectron spectroscopy results indicate clearly a high amount of Sn on the surface. The Conversion Electron Mossbauer unveiled the presence of Fe in the chalcogenide unit cell. The electrochemical characteristics of the synthesized films are also given. (c) 2022 Elsevier B.V. All rights reserved.

15. Enhanced magnetocaloric properties of La0.8K0.2-xPbxMnO3 nanoparticles by optimizing Pb doping concentrations

Authors: Bouzid, SA; Essoumhi, A; Rostas, AM; Kuncser, AC; Negrila, CC; Iacob, N; Galatanu, A; Popescu, B; Sajieddine, M; Galca, AC; Kuncser, V

Published: JUN 15 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.02.239

Polycrystalline La(0.8)K(0.2-x)Pb(x)MnO3 (x = 0.05, 0.10, 0.15, 0.20) ceramics were successfully prepared by flash combustion route and their structural, morphological, magnetic and magnetocaloric properties were investi-gated. Structural analyses using X-ray diffraction reveal that all samples are crystallized in the rhombohedral structure and belong to R <(3) over bar > c space group. The increase of Pb doping does not modify the crystalline structure but changes the grain size and lattice parameters. X-ray photoelectron spectroscopy (XPS) fitting results of Mn 2p peaks confirmed the coexistence of Mn3+ and Mn4+ ions which contribute to the double exchange interactions improving the ferromagnetic order in the samples. The magnetization's temperature and magnetic field de-pendences indicate a second-order ferromagnetic-paramagnetic transition of the ceramics. A significant mag-netic entropy change near room temperature was observed for La0.8K0.1Pb0.1MnO3, showing considerable magnetocaloric properties. Furthermore, electron paramagnetic resonance spectroscopy (EPR) was also used to examine the ferromagnetic-paramagnetic transition.

16. Photodegradation of Azathioprine in the Presence of Sodium Thiosulfate

Authors: Toulbe, N; Smaranda, I; Negrila, C; Bartha, C; Manta, CM; Baibarac, M

Published: APR 2022, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 23, 3975, DOI: 10.3390/ijms23073975

The effect of sodium thiosulfate (ST) on the photodegradation of azathioprine (AZA) was analyzed by UV-VIS spectroscopy, photoluminescence (PL), FTIR spectroscopy, Raman scattering, X-ray photoelectron (XPS) spectroscopy, thermogravimetry (TG) and mass spectrometry (MS). The PL studies highlighted that as the ST concentration increased from 25 wt.% to 75 wt.% in the AZA:ST mixture, the emission band of AZA gradual downshifted to 553, 542 and 530 nm. The photodegradation process of AZA:ST induced: (i) the emergence of a new band in the 320-400 nm range in the UV-VIS spectra of AZA and (ii) a change in the intensity ratio of the photoluminescence excitation (PLE) bands in the 280-335 and 335-430 nm spectral ranges. These changes suggest the emergence of new compounds during the photo-oxidation reaction of AZA with ST. The invoked photodegradation compounds were confirmed by studies of the Raman scattering, the FTIR spectroscopy and XPS spectroscopy through: (i) the downshift of the IR band of AZA from 1336 cm(-1) to 1331 cm(-1), attributed to N-C-N deformation in the purine ring; (ii) the change in the intensity ratio of the Raman lines peaking at 1305 cm(-1) and 1330 cm(-1) from 3.45 to 4.57, as the weight of ST in the AZA:ST mixture mass increased; and (iii) the emergence of a new band in the XPS O1s spectrum peaking at 531 eV, which was associated with the C=O bond. Through correlated studies of TG-MS, the main key fragments of ST-reacted AZA are reported.

17. Ageing studies of Multi-Strip Multi-Gap Resistive Plate Counters based on low resistivity glass electrodes in high irradiation dose

Published: FEB 1 2022, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1024, 166122, DOI: 10.1016/j.nima.2021.166122

Detailed tests and analysis of ageing effects of high irradiation dose on Multi-Strip Multi-Gap Resistive Plate Counters (MSMGRPC) based on low resistivity glass electrodes, foreseen to be used for the most forward polar angles covered by the Time-of Flight (ToF) sub-detector of the Compressed Baryonic Matter (CBM) experiment at Facility for Antiprotons and Ion Research (FAIR) - Darmstadt are reported. The tests were performed at a multi-purpose irradiation facility of IFIN-HH based on Co-60 source. MSMGRPC efficiency, cluster size, surface and volume resistivity of the glass electrodes after irradiation are measured and compared with their values before irradiation. The results of a comprehensive analysis of the composition and properties of the deposited layers on the glass electrodes, based on different methods, i.e. Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), foil Elastic Recoil Detection Analysis (ERDA), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Terahertz Time Domain Spectroscopy (THz-TDS), are presented.

18. Iron-Oxide-Nanoparticles-Doped Polyaniline Composite Thin Films

Authors: Butoi, B; Ciobanu, CS; Iconaru, SL; Negrila, CC; Badea, MA; Balas, M; Dinischiotu, A; Predoi, G; Bita, B; Groza, A; Predoi, D

Published: MAY 2022, POLYMERS, 14, 1821, DOI: 10.3390/polym14091821

Iron-oxide-doped polyaniline (PANI-IO) thin films were obtained by the polymerization of aniline monomers and iron oxide solutions in direct current glow discharge plasma in the absence of a buffer gas for the first time. The PANI-IO thin films were deposited on optical polished Si wafers in order to study surface morphology and evaluate their in vitro biocompatibility. The characterization of the coatings was accomplished using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), metallographic microscopy (MM), and X-ray photoelectron spectroscopy (XPS). In vitro biocompatibility assessments were also conducted on the PANI-IO thin films. It was observed that a uniform distribution of iron oxide particles inside the PANI layers was obtained. The constituent elements of the coatings were uniformly distributed. The Fe-O bonds were associated with magnetite in the XPS studies. The surface morphology of the PANI-IO thin films was assessed by atomic force microscopy (AFM). The AFM topographies revealed that PANI-IO exhibited the morphology of a uniformly distributed and continuous layer. The viability of Caco-2 cells cultured on the Si substrate and PANI-IO coating was not significantly modified compared to control cells. Moreover, after 24 h of incubation, we observed no increase in LDH activity in media in comparison to the control. In addition, our results revealed that the NO levels for the Si substrate and PANI-IO coating were similar to those found in the control sample.

19. Water denitration over titania-supported Pt and Cu by combined photocatalytic and catalytic processes: Implications for hydrogen generation properties in a photocatalytic system

Authors: Vasile, A; Papa, F; Bratan, V; Munteanu, C; Teodorescu, M; Atkinson, I; Anastasescu, M; Kawamoto, D; Negrila, C; Ene, CDD; Spataru, T; Balint, I

Published: APR 2022, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, 10, 107129, DOI: 10.1016/j.jece.2022.107129

The present work provides a new approach to the water denitration process and a facile strategy of catalyst preparation for the efficient hydrogen generation. The main focus of the research reported here was nitrate removal from aqueous solutions and simultaneous hydrogen generation under UV-Vis-light irradiation. This is a very important aspect in case of practical applications, eliminating the external source of hydrogen. Aiming to get a deeper understanding on the role of surface structures (size and shape of nanoparticles) towards the reduction mechanism and to establish basic principles for an efficient process, Pt-Cu/TiO2 and Pt-Cu/TiO2 modified with well-defined Pt nanoparticles were employed. The synthesized materials were characterized using various physicochemical techniques and tested comparatively for: (i) nitrate catalytic reduction by hydrogen (dark reaction) and (ii) nitrate photocatalytic reduction by in-situ generated solar hydrogen. In order to enhance overall denitration reaction by combined photocatalytic and catalytic processes, photo-generated charges and in-situ generated H-2 as reducing agent were used. Improvement of catalytic performances of nitrate hydrogenation reaction (~100% NO3 over line conversion) related to intimate contact between Pt and Cu was obtained. The in-situ generated H-2 by water splitting over the studied catalysts reduces efficiently NO3 over line ions. Enhanced photo-catalytic activity toward solar H-2 production by deposited well-defined Pt nanoparticles (~10 nm) was achieved. In order to make possible decontamination of polluted waters using in-situ generated H-2 under light exposure, the future optimization of such photo-catalytic systems looks promising.

20. Role of vanadium oxide on the lithium silicate glass structure and properties

Authors: Gaddam, A; Allu, AR; Fernandes, HR; Stan, GE; Negrila, CC; Jamale, AP; Mear, FO; Montagne, L; Ferreira, JMF

Published: JUN 2021, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 104, 2505, DOI: 10.1111/jace.17671

The structural role of V in 28Li(2)O-72SiO(2) (in mol%) lithium silicate glass doped with 0.5 mol% V2O5 was assessed using Si-29 and V-51 Nuclear Magnetic Resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopy techniques. Despite the low amount of V2O5 used, the structural information obtained or deduced from the statistical analysis of the NMR data could explain the evolution of glass properties after V2O5 addition. The XPS results indicated that all vanadium exists in 5+ oxidation state. Both the Si-29 NMR and FTIR data point toward an increase in the polymerization of the silicate network, caused by the V2O5 acting as network former, capable to form various QVn tetrahedral units (for n = 0, 1, and 2) in the glasses. These QVn units, which are similar to phosphate units, scavenge the Li+ ions and cause the silicate network to polymerize. However, in an overall balance, the entire glass network is depolymerized due to the additional nonbridging oxygens contributed by the vanadium polyhedra. The addition of vanadium causes the network to expand and increases the ionic conductivity.

21. Effect of Vanadium Oxide on the Structure and Li-Ion Conductivity of Lithium Silicate Glasses

Authors: Gaddam, A; Allu, AR; Ganisetti, S; Fernandes, HR; Stan, GE; Negrila, CC; Jamale, AP; Mear, F; Montagne, L; Ferreira, JMF

Published: AUG 5 2021, JOURNAL OF PHYSICAL CHEMISTRY C, 125, 16857, DOI: 10.1021/acs.jpcc.1c05059

The commercially ubiquitous liquid electrolytes for lithium-ion batteries have several shortcomings in terms of safety. Therefore, development of solid electrolytes, especially those that are glass-based, has been gaining increasing interest in recent times. However, the fundamental understanding of the changes in the glass structure and the corresponding changes in the properties due to the addition of dopants is necessary for the development of glasses. Therefore, here, we report a study on the role of vanadium on the glass structure, ionic conduction, crystallization behavior, and other properties of lithium silicate-based glasses (23Li(2)O-2.64K(2)O-2.64Al(2)O(3)-71.72SiO(2)) as a solid electrolyte for high-temperature Li-ion battery applications. Furthermore, we proposed a mathematical model to describe/quantify the ion-conducting channels' connectivity in glasses. The experimental glass structures were assessed using Si-29, V-51, Al-27 nuclear magnetic resonance, Fourier transform infrared, and ultraviolet-visible spectroscopy techniques. The ionic conductivity was measured by impedance spectroscopy, and the crystallization behavior was studied by optical microscopy and X-ray diffraction. Furthermore, molecular dynamics simulations were also used to gain structural insights of the glasses. In the designed compositions, the addition of vanadium decreased the overall concentration of Li+ ions. However, the results revealed that the ionic conductivity improved with the addition of vanadium in spite of a decrease in the number of charge carriers. This suggests that vanadium makes the pathways easier for the conducting ions. Thus, we conclude that vanadium modifies the conduction channels to promote better hoping of the ions from one site to another.

22. Structural, morphological and optical properties of Cu-Fe-Sn-S thin films prepared by electrodeposition at fixed applied potential

Authors: El Khouja, O; Galca, AC; Nouneh, K; Zaki, MY; Touhami, ME; Taibi, M; Matei, E; Negrila, CC; Enculescu, M; Pintilie, L

Published: MAR 1 2021, THIN SOLID FILMS, 721, DOI: 10.1016/j.tsf.2021.138547

Cu-Fe-Sn-S films were obtained on indium tin oxide / glass substrates by a low-cost electrodeposition using an aqueous solution of CuSO4, FeSO4, SnSO4, and Na2S2O3 at room temperature followed by high-temperature sulfurization (500 degrees C) in argon flow. A range of cathodic potentials have been used for electrodeposition, those being chosen after a preliminary cyclic voltammetry study. The coatings were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray Photoelectron Spectroscopy and conventional spectroscopy (diffuse reflectance and specular transmission). The results are discussed with respect to the used applied potential.

23. Multi-Level Evaluation of UV Action upon Vitamin D Enhanced, Silver Doped Hydroxyapatite Thin Films Deposited on Titanium Substrate

Authors: Negrila, CC; Predoi, D; Ghita, RV; Iconaru, SL; Ciobanu, SC; Manea, M; Badea, ML; Costescu, A; Trusca, R; Predoi, G; Stanciu, GA; Hristu, R; Dragu, LD; Bleotu, C; Groza, A; Marinas, IC; Chifiriuc, MC

Published: FEB 2021, COATINGS, 11, DOI: 10.3390/coatings11020120

Hydroxyapatite Ca-10(PO4)(6)(OH)(2) (HAp) is an important bioactive material for bone tissue reconstruction, due to its highly thermodynamic stability at a physiological pH without bio-resorption. In the present study, the Ag:HAp and the corresponding Ag:HAp + D-3 thin films (similar to 200 nm) coating were obtained by vacuum deposition method on Ti substrate. The obtained samples were exposed to different UV irradiation times, in order to investigate the UV light action upon thin films, before considering this method for the thin film's decontamination. The effects of UV irradiation upon Ag:Hap + D-3 are presented for the first time in the literature, marking a turning point for understanding the effect of UV light on composite biomaterial thin films. The UV irradiation induced an increase in the initial stages of surface roughness of Ag:HAp thin film, correlated with the modifications of XPS and FTIR signals. The characteristics of thin films measured by AFM (RMS) analysis corroborated with XPS and FTIR investigation highlighted a process of recovery of the thin film's properties (e.g., RMS), suggesting a possible adaptation to UV irradiation. This process has been a stage to a more complicated UVA rapid degradation process. The antifungal assays demonstrated that all the investigated samples exhibited antifungal properties. Moreover, the cytotoxicity assays revealed that the HeLa cells morphology did not show any alterations after 24 h of incubation with the Ag:HAp and Ag:HAp + D-3 thin films.

24. Nitrogen and Bromide Co-Doped Hydroxyapatite Thin Films with Antimicrobial Properties

Authors: Iconaru, SL; Ciobanu, CS; Predoi, D; Motelica-Heino, M; Negrila, CC; Badea, ML; Predoi, MV; Chifiriuc, CM; Popa, M

Published: DEC 2021, COATINGS, 11, DOI: 10.3390/coatings11121505

Hydroxyapatite (Ca-10(PO4)(6)(OH)(2), HAp), due to its high biocompatibility, is widely used as biomaterial. Doping with various ions of hydroxyapatite is performed to acquire properties as close as possible to the biological apatite present in bones and teeth. In this research the results of a study performed on thin films of hydroxyapatite co-doped with nitrogen and bromine (NBrHAp) are presented for the first time. The NBrHAp suspension was obtained by performing the adapted co-precipitation method using cetyltrimethylammonium bromide (CTAB). The thin layers of NBrHAp were obtained by spin-coating. The stability of the NBrHAp suspension was examined by ultrasound measurements. The thin layers obtained by the spin-coating method were examined by scanning electron microscopy (SEM), optical microscopy (OM), and metallographic microscopy (MM). The presence of nitrogen and bromine were highlighted by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) studies. Fourier transform infrared spectroscopy (FTIR) was used to highlight the chemical status of nitrogen and bromine. In addition, the powder obtained from the NBrHAp suspension was analyzed by XRD. Moreover, the in vitro antimicrobial activity of the NBrHAp suspensions and coatings was investigated using the reference microbial strains Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. The results highlighted the successful obtainment of N and Br co-doped hydroxyapatite suspension for the first time by an adapted co-precipitation method. The obtained suspension was used to produce pure NBrHAp composite thin films with superior morphological properties. The NBrHAp suspensions and coatings exhibited in vitro antimicrobial activity against bacterial and fungal strains and revealed their good antimicrobial activity.

25. Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Authors: Amarande, L; Cioangher, MC; Toma, V; Miclea, CF; Stefan, M; Pasuk, I; Iuga, AR; Negrila, C; Matei, E; Palici, AM; Joita, AC

Published: DEC 1 2021, CERAMICS INTERNATIONAL, 47, 33389, DOI: 10.1016/j.ceramint.2021.08.243

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)(1-0.015-x)Mn0.015Sbx)O-3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.

26. Zn-Fe-oxide nanostructures of different iron concentrations for multifunctional applications: properties and precursor influence

Authors: Mihalache, V; Negrila, C; Mercioniu, I; Iacob, N; Kuncser, V

Published: AUG 14 2021, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 23, 16127, DOI: 10.1039/d1cp01002f

Zn-Fe-O nanoparticle systems (Z3F, Z20F and Z60F) were produced by changing the Zn:Fe ratio (0.97 : 0.03, 0.8 : 0.2 and 0.4 : 0.6 in at%, respectively) in Zn(ii)-Fe(iii)-carboxylate precursors. According to X-ray diffraction, Z60F is nearly single-phase ZnFe2O4 (5.9 nm crystallite size), Z20F is a ZnO/ZnFe2O4 nanocomposite consisting of 48.8% ZnFe2O4 (4.7 nm crystallite size), and Z3F is apparently pure ZnO (9.5 nm). We found evidence for a ZnFe2O4 spinel of high inversion degree (80-100%) and with superparamagnetic (SPM) behaviour at room temperature in all three samples by a remarkable correlation between HRTEM, FTIR, XPS, Mossbauer and magnetization analyses. Iron modifies the decomposition process of the precursor and enhances its viscosity, which appears to favour the separation of Zn- and Fe-rich phases. As a consequence, two-phase systems of individual nanocrystals/nanoparticles (ZnO and ZnFe2O4) are formed. The large anisotropy constant, 10(6)-10(7) erg cm(-3), of the ZnFe2O4 nanoparticles and the concentration dependence of their magnetic energy barrier are explained in terms of interparticle interactions interlinked with finite size effects and high inversion degree; these factors also control the other parameters of importance for applications, including the blocking temperature (13-111 K), saturation magnetization (1.08-17.7 emu g(-1) at 300 K, 4.6-44.8 emu g(-1) at 5 K) and coercivity (85.4-491 Oe at 5 K). Magnetic dynamic results, particularly modelled by the Neel-Brown and Vogel-Fulcher laws, yield fitting parameters which validate the presence of concentration-dependent dipole-like interactions between ZnFe2O4 nanoparticles. A fraction of iron was found in the Fe2+ state, presumably substituting for Zn2+ in zinc oxide; however, the samples behave like ZnFe2O4 SPM nanoclusters/nanoparticles dispersed in a nonmagnetic ZnO particle assembly, rather than Zn(Fe)O dilute magnetic semiconductors. The relevance of the properties of the investigated material for specific applications is highlighted throughout the manuscript.

27. EPR spectroscopy and structural investigations, of Eu2+-doped chloroborate glass-ceramic

Authors: Secu, M; Kuncser, A; Negrila, C; Rostas, AM

Published: DEC 15 2021, CERAMICS INTERNATIONAL, 47, 35095, DOI: 10.1016/j.ceramint.2021.09.051

Europium doped (0.1% and 1%) chlomborate BaO-B2O3-BaCl2 glass and glass-ceramic with embedded BaCl2 nanocrystals have been synthesised, investigated, and compared with the corresponding nanocrystalline powder. The structural analysis of the glass evidenced ionic bonds characteristic to the glass host structure and compositional changes during the melting. X-ray diffraction and transmission electron microscopy revealed the formation of orthorhombic BaCl2 nanocrystals of about tens on nm in size and a smaller amount of BaB2O4 nanocrystals. Structural analysis of the Eu2+-doped BaCl2 nanocrystals has shown a distortion of the crystalline cell assigned to the growth process, affected by defects and ionic impurities. Photoluminescence spectra of the glass-ceramic revealed Eu3+ and Eu2+ luminescent ion species, but only Eu2+ is incorporated within the BaCl2 nanocrystalline phase. Electron paramagnetic resonance measurements in X-band sustain the presence of Eu2+ ions. The EPR parameters (g values and hyperfine constants) resulting from the Q-band EPR spectra simulations recorded on glass-ceramic are similar to those in Eu2+-doped BaCl2 and confirmed the partial incorporation of Eu2+ ions within the BaCl2:Eu2+ nanocrystals in the glass-ceramics.

28. Cytotoxicity, Antioxidant, Antibacterial, and Photocatalytic Activities of ZnO-CdS Powders (vol 13, 182, 2020)

Authors: Zgura, I; Preda, N; Enculescu, M; Diamandescu, L; Negrila, C; Bacalum, M; Ungureanu, C; Barbinta-Patrascu, ME

Published: DEC 2021, MATERIALS, 14, DOI: 10.3390/ma14247713

29. Nitrogen Functionalization of CVD Grown Three-Dimensional Graphene Foam for Hydrogen Evolution Reactions in Alkaline Media

Authors: Ion-Ebrasu, D; Andrei, RD; Enache, S; Caprarescu, S; Negrila, CC; Jianu, C; Enache, A; Boerasu, I; Carcadea, E; Varlam, M; Vasile, BS; Ren, JW

Published: SEP 2021, MATERIALS, 14, DOI: 10.3390/ma14174952

Three-dimensional graphene foam (3D-GrFoam) is a highly porous structure and sustained lattice formed by graphene layers with sp(2) and sp(3) hybridized carbon. In this work, chemical vapor deposition (CVD)-grown 3D-GrFoam was nitrogen-doped and platinum functionalized using hydrothermal treatment with different reducing agents (i.e., urea, hydrazine, ammonia, and dihydrogen hexachloroplatinate (IV) hydrate, respectively). X-ray photoelectron spectroscopy (XPS) survey showed that the most electrochemically active nitrogen-doped sample (GrFoam3N) contained 1.8 at % of N, and it exhibited a 172 mV dec(-1) Tafel plot associated with the Volmer-Heyrovsky hydrogen evolution (HER) mechanism in 0.1 M KOH. By the hydrothermal process, 0.2 at % of platinum was anchored to the graphene foam surface, and the resultant sample of GrFoamPt yielded a value of 80 mV dec(-1) Tafel associated with the Volmer-Tafel HER mechanism. Furthermore, Raman and infrared spectroscopy analysis, as well as scanning electron microscopy (SEM) were carried out to understand the structure of the samples.

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

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

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

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

31. Spectroscopic studies on photodegradation of atorvastatin calcium

Authors: Oprica, M; Iota, M; Daescu, M; Fejer, SN; Negrila, C; Baibarac, M

Published: JUL 28 2021, SCIENTIFIC REPORTS, 11, DOI: 10.1038/s41598-021-94693-5

In this work, the photodegradation process of atorvastatin calcium (ATC) is reported as depending on: (1) the presence and the absence of excipients in the solid state; (2) the chemical interaction of ATC with phosphate buffer (PB) having pH equal to 7 and 8; and (3) hydrolysis reaction of ATC in the presence of aqueous solution of NaOH. The novelty of this work consists in the monitoring of the ATC photodegradation by photoluminescence (PL). The exposure of ATC in solid state to UV light induces the photo-oxygenation reactions in the presence of water vapors and oxygen from air. According to the X-ray photoelectron spectroscopic studies, we demonstrate that the photo-oxygenation reaction leads to photodegradation compounds having a high share of C=O bonds compared to ATC before exposure to UV light. Both in the presence of PB and NaOH, the photodegradation process of ATC is highlighted by a significant decrease in the intensity of the PL and photoluminescence excitation (PLE) spectra. According to PLE spectra, the exposure of ATC in the presence of NaOH to UV light leads to the appearance of a new band in the spectral range 340-370 nm, this belonging to the photodegradation products. Arguments concerning the chemical compounds, that resulted in this last case, are shown by Raman scattering and FTIR spectroscopy.

32. Poly(Vinyl Chloride) Spheres Coated with Graphene Oxide Sheets: From Synthesis to Optical Properties and Their Applications as Flame-Retardant Agents

Authors: Baibarac, M; Stingescu, L; Stroe, M; Negrila, C; Matei, E; Cotet, LC; Anghel, I; Sofran, IE; Baia, L

Published: FEB 2021, POLYMERS, 13, DOI: 10.3390/polym13040565

A new method to obtain poly(vinyl chloride) (PVC) spheres, which consists of an interaction between commercial PVC grains and hexyl ethyl cellulose and lauroyl peroxide at a temperature of 60 degrees C, is reported. The addition of the graphene oxide (GO) sheets dispersed in dimethylformamide to the reaction mixture leads to the generation of composites made of PVC spheres coated with GO sheets. Scanning electron microscopy studies have demonstrated that this method allows for the transformation of PVC grains with sizes between 75 and 227 mu m into spheres with sizes varying from 0.7 to 3.5 mu m when the GO concentration in the PVC/GO composite mass increases from 0.5 to 5 wt.%. Our studies of Raman scattering and FTIR spectroscopy highlight a series of changes that indicate the appearance of ClCH=CH-, CH2=CCl-, and/or -CH=CCl- units as a result of PVC partial dehydrogenation. New -COO- and C-OH bonds on the GO sheet surfaces are induced during the preparation of PVC spheres coated with GO sheets. A photoluminescence (PL) band with a maximum at 325 nm is reported to characterize the PVC spheres. A PVC PL quenching process is demonstrated to be induced by the increase in the concentration of the GO sheets in the PVC/GO composite mass. The perspectives regarding the use of this composite as a flame-retardant material are also reported.

33. Cytotoxicity, Antioxidant, Antibacterial, and Photocatalytic Activities of ZnO-CdS Powders

Authors: Zgura, I; Preda, N; Enculescu, M; Diamandescu, L; Negrila, C; Bacalum, M; Ungureanu, C; Barbinta-Patrascu, ME

Published: JAN 1 2020, MATERIALS, 13, DOI: 10.3390/ma13010182

In this work, ZnO-CdS composite powders synthesized by a simple chemical precipitation method were thoroughly characterized. The morphological, structural, compositional, photocatalytical, and biological properties of the prepared composites were investigated in comparison with those of the pristine components and correlated with the CdS concentration. ZnO-CdS composites contain flower-like structures, their size being tuned by the CdS amount added during the chemical synthesis. The photocatalytic activity of the composites was analyzed under UV irradiation using powders impregnated with methylene blue; the tests confirming that the presence of CdS along the ZnO in composites can improve the dye discoloration. The biological properties such as antioxidant capacity, antibacterial activity, and cytotoxicity of the ZnO, CdS, and ZnO-CdS composites were evaluated. Thus, the obtained composites presented medium antioxidant effect, biocidal activity against Escherichia coli, and no toxicity (at concentrations less than 0.05 mg/mL for composites with a low CdS amount) for human fibroblast cells. Based on these results, such composites can be used as photocatalytic and/or biocidal additives for photoactive coatings, paints, or epoxy floors, which in their turn can provide a cleaner and healthier environment.

34. Strategy for Modifying Layered Perovskites toward Efficient Solar Light-Driven Photocatalysts for Removal of Chlorinated Pollutants

Authors: Raciulete, M; Papa, F; Negrila, C; Bratan, V; Munteanu, C; Pandele-Cusu, J; Culita, DC; Atkinson, I; Balint, I

Published: JUN 2020, CATALYSTS, 10, DOI: 10.3390/catal10060637

We have explored an efficient strategy to enhance the overall photocatalytic performances of layered perovskites by increasing the density of hydroxyl group by protonation. The experimental procedure consisted of the slow replacement of interlayer Rb(+)cation of RbLaTa(2)O(7)Dion-Jacobson (DJ) perovskite by H(+)via acid treatment. Two layered perovskites synthesized by mild (1200 degrees C for 18 h) and harsh (950 and 1200 degrees C, for 36 h) annealing treatment routes were used as starting materials. The successful intercalation of proton into D-J interlayer galleries was confirmed by FTIR spectroscopy, thermal analyses, ion chromatography and XPS results. In addition, the ion-exchange route was effective to enlarge the specific surface area, thus enhancing the supply of photocharges able to participate in redox processes involved in the degradation of organic pollutants. HLaTa_01 protonated layered perovskite is reported as a efficient photocatalyst for photomineralization of trichloroethylene (TCE) to Cl(-)and CO(2)under simulated solar light. The enhanced activity is attributed to combined beneficial roles played by the increased specific surface area and high density of hydroxyl groups, leading to an efficiency of TCE mineralization of 68% moles after 5 h of irradiation.

35. Development of Cerium-Doped Hydroxyapatite Coatings with Antimicrobial Properties for Biomedical Applications

Authors: Predoi, D; Iconaru, SL; Predoi, MV; Groza, A; Gaiaschi, S; Rokosz, K; Raaen, S; Negrila, CC; Prodan, AM; Costescu, A; Badea, ML; Chapon, P

Published: JUN 2020, COATINGS, 10, DOI: 10.3390/coatings10060516

Antibacterial cerium-doped hydroxyapatite (Ce-HAp) layers have been researched sparingly in recent years. The Ce-HAp powder, Ca10-xCex(PO4)(6)(OH()2)with x(Ce)= 0.05, was obtained by an adapted chemical co-precipitation method at room temperature. The target was prepared using the Ce-HAp (x(Ce)= 0.05) powder sintered in air at 600 degrees C. The coatings on the Ti substrate were generated in plasma using a radio frequency (RF) magnetron sputtering discharge in an Ar gas flow in a single run. To collect the most complete information regarding the antimicrobial activity of cerium-doped hydroxyapatite with x(Ce)= 0.05, (5Ce-HAp), antimicrobial studies were carried out both on the final suspensions and on the coated surfaces. The target was tested using ultrasound measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), glow-discharge optical emission spectroscopy (GDOES), and X-ray photoelectron spectroscopy (XPS). The present study exhibited for the first time results of the homogeneous coatings of hydroxyapatite doped with cerium using a radio frequency magnetron sputtering technique. In addition, this study highlighted for the first time the stability of the cerium-doped hydroxyapatite gels used in the creation of the coating. Ultrasound measurements on the concentrated suspension of 5Ce-HAp showed a good stability compared to double distilled, water which was chosen as the reference fluid. Particles with spherical shape were observed by both TEM and SEM analysis. The broadening of the IR bands in the IR spectrum of the 5Ce-HAp film in comparison with the IR spectrum of the precursor target indicate the formation of interlinked bonds into the layer bulk. XPS analysis revealed that the mixture of Ce(3+)and Ce(4+)ions in the hydroxyapatite (HAp) structure of the coatings could be due to the deposition process. The surface of 5Ce-HAp coatings was homogenous with particles having a spherical shape. A uniform distribution of all the constituent elements on the surface the 5Ce-HAp layer was revealed. The antimicrobial assays proved that both 5Ce-HAp suspensions and 5Ce-HAp coatings effectively inhibited the development of colony forming units (CFU) for all the tested microbial strains. Moreover, the antimicrobial assays emphasized that the 5Ce-HAp suspensions had a biocide effect against Escherichia coli (E. coli) andCandida albicans(C. albicans)microbial strains after 72 h of incubation.

36. Influence of Reduced Graphene Oxide on the Electropolymerization of 5-Amino-1-naphthol and the Interaction of 1,4-Phenylene Diisothiocyanate with the Poly(5-Amino-1-naphtol)/Reduced Graphene Oxide Composite

Authors: Baibarac, M; Daescu, M; Socol, M; Bartha, C; Negrila, C; Fejer, SN

Published: JUN 2020, POLYMERS, 12, DOI: 10.3390/polym12061299

A new composite base on reduced graphene oxide (RGO) and poly(5-amino-1-naphthol) (P5A1N) was synthesized by the electrochemical polymerization of 5-amino-1-naphthol (5A1N) in the presence of HClO(4)and H(4)SiW(12)O(40)onto the surface of Au electrode covered with the RGO sheets. The linear dependence of the current densities of the anodic and cathodic peaks with the scan rate of the potential range (0; 0.8) V vs. SCE, reported during electropolymerization of 5A1N, indicates an electron transfer that is controlled by diffusion. A covalent functionalization of the RGO sheets with P5A1N is argued by: (i) the simultaneous disappearance of the IR band at 1584 cm(-1)and the appearance of the new IR bands at 812, 976 and 3744 cm(-1), and (ii) the appearance of two Raman lines at 738 and 1428 cm(-1). An application of the RGO sheets covalently functionalized with P5A1N is demonstrated to support 1,4-phenylene diisothiocyanate (PDITC), a compound used as a cross-linking agent for various biological applications. The chemical adsorption of PDITC onto the RGO sheets covalently functionalized with P5A1N, which involves the appearance of new functional groups of the type thiourea, was proven by Raman scattering and IR spectroscopy.

37. Highly Active Transition Metal-Promoted CuCeMgAlO Mixed Oxide Catalysts Obtained from Multicationic LDH Precursors for the Total Oxidation of Methane

Authors: Al-Aani, HMS; Trandafir, MM; Fechete, I; Leonat, LN; Badea, M; Negrila, C; Popescu, I; Florea, M; Marcu, IC

Published: JUN 2020, CATALYSTS, 10, DOI: 10.3390/catal10060613

To improve the catalytic performance of an active layered double hydroxide (LDH)-derived CuCeMgAlO mixed oxide catalyst in the total oxidation of methane, it was promoted with different transition-metal cations. Thus, two series of multicationic mixed oxides were prepared by the thermal decomposition at 750 degrees C of their corresponding LDH precursors synthesized by coprecipitation at constant pH of 10 under ambient atmosphere. The first series of catalysts consisted of four M(3)CuCeMgAlO mixed oxides containing 3 at.% M (M = Mn, Fe, Co, Ni), 15 at.% Cu, 10 at.% Ce (at.% with respect to cations), and with Mg/Al atomic ratio fixed to 3. The second series consisted of four Co(x)CuCeMgAlO mixed oxides withx= 1, 3, 6, and 9 at.% Co, while keeping constant the Cu and Ce contents and the Mg/Al atomic ratio. All the mixed oxides were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersion analysis (EDX), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption at -196 degrees C, temperature-programmed reduction under hydrogen (H-2-TPR), and diffuse reflectance UV-VIS spectroscopy (DR UV-VIS), while thermogravimetric and differential thermal analyses (TG-DTG-DTA) together with XRD were used for the LDH precursors. The catalysts were evaluated in the total oxidation of methane, a test reaction for volatile organic compounds (VOC) abatement. Their catalytic performance was explained in correlation with their physicochemical properties and was compared with that of a reference Pd/Al(2)O(3)catalyst. Among the mixed oxides studied, Co(3)CuCeMgAlO was found to be the most active catalyst, with a temperature corresponding to 50% methane conversion (T-50) of 438 degrees C, which was only 19 degrees C higher than that of a reference Pd/Al(2)O(3)catalyst. On the other hand, this T(50)value was ca. 25 degrees C lower than that observed for the unpromoted CuCeMgAlO system, accounting for the improved performance of the Co-promoted catalyst, which also showed a good stability on stream.

38. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions

Authors: Daescu, Monica; Matea, Adelina; Negrila, Catalin; Serbschi, Constantin; Ion, Alina C; Baibarac, Mihaela

Published: Oct 07 2020 , , DOI: 10.3390/molecules25194571

39. The enhancement mechanism of dielectric properties of Pb(Zr,Ti)O-3 via (Mg2+,Sb3+) incorporation for supercapacitors

Authors: Craciun, F; Dimitriu, E; Vasile, BS; Negrila, CC; Trusca, R; Birjega, R; Cernea, M

Published: DEC 2020, MATERIALS TODAY CHEMISTRY, 18, DOI: 10.1016/j.mtchem.2020.100350

Due to the extraordinary versatility of the perovskite structure in accommodating different dopant ions in its structure, in recent years a huge number of multifunctional perovskite materials have been developed. In this work we aim to obtain high temperature-stable and huge dielectric constant materials for supercapacitors by doping divalent Mg2+ and trivalent Sb3+ ions into the octahedral sites, and divalent Sr2+ ions into the dodecahedral sites of lead zirconate-titanate perovskite. The resulting (Pb0.95Sr0.05)(Zr0.425Ti0.45Mg0.042Sb0.083)O3-delta is examined by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), dielectric spectroscopy (DS) and resonance dielectric spectroscopy (RDS) in order to correlate composition, local structure, ion valence and chemical environment of the doped material with the dielectric properties. HRTEM evidences that a composite structure, with co-existent ferroelectric domains and relaxor nanodomains, is formed by doping. XPS shows that Sb3+ and Mg2+ substitute for the Ti4+/Zr4+ ions, pointing to these strong defects as the main cause for the appearance of the relaxor phase. DS and RDS found that the ferroelectric lead zirconate-titanate transforms into a re-entrant relaxorferroelectric composite with a huge dielectric constant of about 10(4) which remains stable (within +/- 10%) in the high temperature range up to 250 degrees C, pointing to this mechanism of relaxor phase re-entrance below the normal ferroelectric phase transition, as being responsible for the enhancement. (C) 2020 Elsevier Ltd. All rights reserved.

40. Novel Ecogenic Plasmonic Biohybrids as Multifunctional Bioactive Coatings

Authors: Barbinta-Patrascu, ME; Ungureanu, C; Badea, N; Bacalum, M; Lazea-Stoyanova, A; Zgura, I; Negrila, C; Enculescu, M; Burnei, C

Published: JUL 2020, COATINGS, 10, DOI: 10.3390/coatings10070659

The objective of the present study is the valorization of natural resources and the recycling of vegetal wastes by converting them into novel plasmonic bio-active hybrids. Thus, a "green" approach was used to design pectin-coated bio-nanosilver. Silver nanoparticles were generated from two common garden herbs (Mentha piperitaandAmaranthus retroflexus), and pectin was extracted from lemon peels. The samples were characterized by the following methods: Ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier Transform Infrared (FT-IR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), dynamic light scattering (DLS), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM)-Energy-dispersive X-ray Spectroscopy (EDX), and zeta potential measurements. Microscopic investigations revealed the spherical shape and the nano-scale size of the prepared biohybrids. Their bioperformances were checked in terms of antioxidant and antibacterial activity. The developed plasmonic materials exhibited a strong ability to scavenge short-life (96.1% divided by 98.7%) and long-life (39.1% divided by 91%) free radicals. Microbiological analyses demonstrated an impressive antibacterial effectiveness of pectin-based hybrids againstEscherichia coli. The results are promising, and the obtained biomaterials could be used in many bio-applications, especially as antioxidant and antimicrobial biocoatings.

41. Surface states mediated charge transfer in redox behavior of hemin at GaAs(100) electrodes

Authors: Enache, M; Negrila, C; Lazarescu, V

Published: MAR 29 2020, RSC ADVANCES, 10, 12325, DOI: 10.1039/d0ra01508c

EIS and XPS investigations on the interaction of hemin with p- and n-doped GaAs(100) electrodes in PBS solution revealed significant differences concerning both the adsorbed species and the mechanism of the redox process caused by dopant nature. XPS data show that hemin is adsorbed on p-GaAs(100) by its carboxyl groups and adopts a vertical position favorable to a polymeric film formation whereas on n-GaAs(100), the adsorbed hemin is monomeric and has a rather planar configuration involving mainly the OH groups of the organic molecule. Hemin gives rise to a reversible redox process at the p-GaAs(100) electrode whereas at n-GaAs(100), there is only one reduction wave of a considerably lower current density appearing at a more negative potential. The effects of the applied potential on the phase angle measured at p-GaAs(100) point out major changes not only in the insulating properties of the adsorbed layer, as found at n-GaAs(100), but also in the electronic properties of the semiconductor triggered by the hemin redox process. Analysis of the experimental data points to a mechanism of charge transfer through surface states, the observed differences being related to the location of the surface states with respect to the formal potential of the hemin redox couple.

42. Influence of boric acid concentration on the properties of electrodeposited CZTS absorber layers

Authors: Zaki, MY; Nouneh, K; Touhami, ME; Matei, E; Badica, P; Burdusel, M; Negrila, CC; Baibarac, M; Pintilie, L; Galca, AC

Published: MAY 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab6afd

This work involves the synthesis and characterization of Cu2ZnSnS4 (CZTS) layers. The films were prepared on Mo/glass substrates by single-step electrodeposition method followed by sulfurization at 500 degrees C under argon flow. The effect of boric acid concentration on the crystallographic structure, compositional and morphological properties of CZTS films was investigated, with the objective to understand the growth behavior and to enhance the film properties. Cyclic Voltammetry was used in order to estimate the adequate deposition potential for the CZT alloy. The x-ray diffraction analysis showed the formation of the kesterite phase in all the samples. The Raman and x-ray photoelectron spectroscopy studies confirmed the existence of the CZTS phase. The scanning electron microscopy was employed to inspect the films structure. The results indicated that increasing the concentration of boric acid affects the physico-chemical properties of the films.

43. Temperature dependence and defect related structure, photoluminescence, (ferro)magnetism and ammonia sensitivity of un-doped nanocrystalline ZnO

Authors: Mihalache, V; Secu, M; Negrila, C; Bercu, V; Mercioniu, I; Leca, A

Published: DEC 2020, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 262, DOI: 10.1016/j.mseb.2020.114748

ZnO nanostructures with intrinsic and extended defects were prepared by rapid decomposition of zinc-propio-nate and annealing at 400 degrees C-970 degrees C. The correlation between the structure/morphology, type of native defects (photoluminescence (PL), EPR) and ferromagnetism was investigated, together with ammonia adsorption capacity. All the samples show room temperature ferromagnetism (RTFM). Crystallite size increases while the unit cell volume, c-axis constant, microstrain and saturation magnetization relax with increasing temperature; morphology varies from aggregated nanoparticles to frameworks of well-welded crystals. 400 degrees C-800 degrees C annealed samples show a broad visible and/or a prominent violet-blue PL emission and, two narrow g = 2.0065 and g = 1.9632 EPR signals. 800 degrees C-970 degrees C annealed samples exhibit very intense green-yellow photoluminescence. The intrinsic defects in conjunction with a deformed lattice and/or pinned by grain-boundaries appear responsible for RTFM and Curie temperature exceeding 700 degrees C. Tuning the morphology, PL intensity and ferromagnetic signal by choice of annealing temperature can find applications in (gas) sensing, photonic/optoelectronic and spintronic devices.

44. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions

Authors: Daescu, M; Matea, A; Negrila, C; Serbschi, C; Ion, AC; Baibarac, M

Published: OCT 2020, MOLECULES, 25, DOI: 10.3390/molecules25194571

In this work, new evidence for the photodegradation reactions of acetaminophen (AC) is reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. Under excitation wavelength of 320 nm, AC shows a PL band in the spectral range of 340-550 nm, whose intensity decreases by exposure to UV light. The chemical interaction of AC with the NaOH solutions, having the concentration ranging between 0.001 and 0.3 M, induces a gradual enhancement of the photoluminescence excitation (PLE) and PL spectra, when the exposure time of samples at the UV light increases until 140 min, as a result of the formation of p-aminophenol and sodium acetate. This behavior is not influenced by the excipients or other active compounds in pharmaceutical products as demonstrated by PLE and PL studies. Experimental arguments for the obtaining of p-aminophenol and sodium acetate, when AC has interacted with NaOH, are shown by Raman scattering and FTIR spectroscopy.

45. Towards a Correlation between Structural, Magnetic, and Luminescence Properties of CeF3:Tb(3+)Nanocrystals

Authors: Bartha, C; Secu, C; Matei, E; Negrila, C; Leca, A; Secu, M

Published: JUL 2020, MATERIALS, 13, DOI: 10.3390/ma13132980

In this study, we report on the structural, magnetic, and optical properties of Tb3+-doped CeF(3)nanocrystals prepared via a polyol-assisted route, followed by calcination. X-ray diffraction analysis and electron microscopy investigations have shown the formation of a dominant Ce(0.75)F(3)nanocrystalline phase (of about 99%), with a relatively uniform distribution of nanocrystals about 15 nm in size. Magnetization curves showed typical paramagnetic properties related to the presence of Ce(3+)and Tb(3+)ions. The magnetic susceptibility showed a weak inflexion at about 150 K, assigned to the cerium ions' crystal field splitting. Under UV light excitation of the Ce(3+)ions, we observed Tb(3+)green luminescence with a quantum yield of about 20%.

46. The Beneficial Mechanical and Biological Outcomes of Thin Copper-Gallium Doped Silica-Rich Bio-Active Glass Implant-Type Coatings

Authors: Stan, GE; Tite, T; Popa, AC; Chirica, IM; Negrila, CC; Besleaga, C; Zgura, I; Sergentu, AC; Popescu-Pelin, G; Cristea, D; Ionescu, LE; Necsulescu, M; Fernandes, HR; Ferreira, JMF

Published: NOV 2020, COATINGS, 10, DOI: 10.3390/coatings10111119

Silica-based bioactive glasses (SBG) hold great promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial efficacy. In the framework of this study, the FastOs(R)BG alkali-free SBG system (mol%: SiO2-38.49, CaO-36.07, P2O5-5.61, MgO-19.24, CaF2-0.59), with CuO (2 mol%) and Ga2O3 (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (similar to 600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (R-RMS < 1 nm) and hydrophilic (water contact angle of similar to 65 degrees). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs(R)BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of similar to 53 MPa, Lc3 critical load value of similar to 4.9 N, hardness of similar to 6.1 GPa and an elastic modulus of similar to 127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the Staphylococcus aureus bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in great demand nowadays.

47. Charge separation and ROS generation on tubular sodium titanates exposed to simulated solar light

Authors: Preda, S; Anastasescu, C; Balint, I; Umek, P; Sluban, M; Negrila, CC; Angelescu, DG; Bratan, V; Rusu, A; Zaharescu, M

Published: MAR 15 2019, APPLIED SURFACE SCIENCE, 470, 1063, DOI: 10.1016/j.apsusc.2018.11.194

The research focuses on a few key points concerning the light-driven processes taking place on TiO2 anatase and sodium titanates with tubular morphology, such as the relationship between the morphology and activity for H-2 and CO2 production, density of surface hydroxyl groups, ROS (center dot OH and center dot O-2(-)) production and photocatalytic activity, and charge separation at the interface of semiconducting domains and enhancement of activity. One key point discussed is whether the materials with peculiar morphologies (i.e. tubular) are superior to the conventional ones. The experimental evidences show that the main advantage of the tubular morphology of sodium titanate is given by its significantly higher surface area compared to parental anatase. FTIR and XPS progressive analyses evidence that the density of surface hydroxyl groups decreases with the development of the tubular morphology. The radical trapping experiments show that the variation of surface hydroxyl density is, generally, followed by activities for center dot OH and center dot O-2(-) generation, as well as by the photocatalytic production of H-2 and CO2 from water/methanol mixture. Consequently, the ROS, formed by action of photogenerated electrons and holes on adsorbed O-2 and hydroxyl groups, respectively, play an important role in determining the photocatalytic activity of titania-based materials. The other major aspect revealed by this research is that the charge separation at the interfaces formed between anatase and sodium titanate crystalline phases has remarkable effect on the activity formation rates of H-2 and CO2.

48. Effect of dilute doping and non-equilibrium synthesis on the structural, luminescent and magnetic properties of nanocrystalline Zn1-xNixO (x=0.0025-0.03)

Authors: Mihalache, V; Negrila, C; Bercu, V; Secu, M; Vasile, E; Stan, GE

Published: JUL 2019, MATERIALS RESEARCH BULLETIN, 115, 48, DOI: 10.1016/j.materresbull.2019.03.001

We report on the influence of dilute doping combined with the processing conditions on the morphological, structural, chemical states, photoluminescence and magnetic properties of Zn1-xNixO nanopowders. Ni doping changes the ZnO powder morphology from randomly-aggregated nanocrystals to densely-packed nanocrystals arranged in columnar particles, modifies the high-energy-component of O1 s spectrum and increases the modified Auger parameter in XPS, enhances the blue photoluminescence (PL) emission, suppresses the green PL emission and the intensity of the g = 1.997 EPR signal. Ni-ZnO nanostructures show room-temperature ferro-magnetism (implying they can serve as dilute magnetic semiconductors). The saturation magnetization, crystallite size and microstrain increase with the doping level; the c-axis constant and unit cell volume decrease, however, being unexpectedly higher with respect to a (reference) ZnO powder with a relaxed lattice. We demonstrate that the investigated properties were controlled by both (dilute) doping level and donor native defects produced by non-equilibrium (oxygen-deficiency and high rate of) ZnO formation.

49. CuxCeMgAlO mixed oxide catalysts derived from multicationic LDH precursors for methane total oxidation

Authors: Al-Aani, HMS; Iro, E; Chirra, P; Fechete, I; Badea, M; Negrila, C; Popescu, I; Olea, M; Marcu, IC

Published: SEP 25 2019, APPLIED CATALYSIS A-GENERAL, 586, DOI: 10.1016/j.apcata.2019.117215

A series of five Cu(x)CeMgAlO mixed oxides with different copper contents (x) ranging from 6 to 18 at. % with respect to cations, but with fixed 10 at. % Ce and Mg/Al atomic ratio of 3, were prepared by thermal decomposition of layered double hydroxide (LDH) precursors at 750 degrees C. The solid containing 15 at. % Cu, i.e. Cu (15)CeMgAlO, was also calcined at 550 and 650 degrees C. Powder XRD was used to characterize the crystalline structure and SEM-EDX was used to monitor the morphology and chemical composition of both as prepared and calcined materials. Additionally, the textural properties and the reducibility of the mixed oxide catalysts were studied by nitrogen adsorption/desorption and temperature programmed reduction with hydrogen (H-2-TPR) techniques, respectively. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical state of the elements on the catalyst surface and the diffuse reflectance UV-vis spectroscopy, to obtain information about the stereochemistry and aggregation of copper in the Cu-containing mixed oxides. Their catalytic properties in the total oxidation of methane, used as a volatile organic compound (VOC) model molecule, were evaluated and compared with those of an industrial Pd/Al2O3 catalyst. Their catalytic behavior was explained in correlation with their physicochemical properties. Cu(15)CeMgAlO mixed oxide was shown to be the most active catalyst in this series, with a T-50 (temperature corresponding to 50% methane conversion) value of only ca. 45 degrees C higher than that of a commercial Pd/Al2O3 catalyst. This difference becomes as low as ca. 25 degrees C for the Cu(15)CeMgAlO system calcined at 550 degrees C. The influences of the contact time and of the methane concentration in the feed gas on the catalytic performances of the Cu(15)CeMgAlO catalyst have been investigated and its good stability on stream was evidenced.

50. Rapid thermal annealing for high-quality ITO thin films deposited by radio-frequency magnetron sputtering

Authors: Prepelita, P; Stavarache, I; Craciun, D; Garoi, F; Negrila, C; Sbarcea, BG; Craciun, V

Published: JUL 25 2019, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 10, 1522, DOI: 10.3762/bjnano.10.149

In this work, rapid thermal annealing (RTA) was applied to indium tin oxide (ITO) films in ambient atmosphere, resulting in significant improvements of the quality of the ITO films that are commonly used as conductive transparent electrodes for photovoltaic structures. Starting from a single sintered target (purity 99.95%), ITO thin films of predefined thickness (230 nm, 300 nm and 370 nm) were deposited at room temperature by radio-frequency magnetron sputtering (rfMS). After deposition, the films were subjected to a RTA process at 575 degrees C (heating rate 20 degrees C/s), maintained at this temperature for 10 minutes, then cooled down to room temperature at a rate of 20 degrees C/s. The film structure was modified by changing the deposition thickness or the RTA process. X-ray diffraction investigations revealed a cubic nanocrystalline structure for the as-deposited ITO films. After RTA, polycrystalline compounds with a textured (222) plane were observed. X-ray photon spectroscopy was used to confirm the beneficial effect of the RTA treatment on the ITO chemical composition. Using a Tauc plot, values of the optical band gap ranging from 3.17 to 3.67 eV were estimated. These values depend on the heat treatment and the thickness of the sample. Highly conductive indium tin oxide thin films (rho = 7.4 x 10(-5) Omega cm) were obtained after RTA treatment in an open atmosphere. Such films could be used to manufacture transparent contact electrodes for solar cells.

51. The influence of the nanocrystals size and surface on the Yb/Er doped LaF3 luminescence properties

Authors: Secu, CE; Matei, E; Negrila, C; Secu, M

Published: JUN 30 2019, JOURNAL OF ALLOYS AND COMPOUNDS, 791, 1104, DOI: 10.1016/j.jallcom.2019.03.267

Up-conversion luminescence and thermoluminescence properties of LaF3 nanocrystals, with sizes of about 20 nm, were studied and discussed in relation to -size and surface related effects. XPS spectra have evidenced the presence of oxidized Er and La ions within a thin layer (of about 1 nm thickness) at the nanocrystals surface, as well as Yb ions bonded with fluorine ions. The green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion emissions of Er3+ ions are influenced by the relative dominance of Erions that reside within the thin oxidized layer. The broad thermoluminescence curves are assigned to the recombination of trap defects associated with surface states and within the oxidized surface layer. (C) 2019 Elsevier B.V. All rights reserved.

52. Photoluminescence and structural properties of the nitrogen doped TiO2 and the influence of SiO2 and Ag nanoparticles

Authors: Nila, A; Baibarac, M; Udrescu, A; Smaranda, I; Mateescu, A; Mateescu, G; Mereuta, P; Negrila, CC

Published: SEP 18 2019, JOURNAL OF PHYSICS-CONDENSED MATTER, 31, DOI: 10.1088/1361-648X/ab2692

Mixtures of nitrogen-doped titanium dioxide (TiO2:N) with different concentrations of Ag and/or SiO2 particles (0.5, 1 and 2 wt.%) were prepared in solid state by mechanico-chemical interactions. Using UV-VIS spectroscopy, Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE), the influence of the particles on the host material is evaluated. UV-VIS spectroscopy studies indicate a TiO2:N band gap shift to the UV range with increasing concentrations of SiO2 and Ag particles. PL intensities decrease with increasing concentrations of Ag and/or SiO2 particles in the TiO2:N host matrix, which in turn could effectively restrict the electron and hole recombination. To explain these processes, the different de-excitation ways will be advanced, taking into account the energy levels diagram of TiO2:N/Ag, TiO2:N/SiO2 and TiO2:N/Ag/SiO2 systems. PLE spectra show a gradual decrease in their relative intensities after 165 min of continuous irradiation due to photosensitivity of TiO2:N. The plasmonic effect of Ag particles in the TiO2:N/Ag system is highlighted for the first time by PLE studies.

53. Photoluminescence and thermoluminescence properties of the Sr3Al2O6:Eu3+/Eu2+,Tb3+ persistent phosphor

Authors: Gingasu, D; Mindru, I; Ianculescu, A; Preda, S; Negrila, C; Secu, M

Published: OCT 2019, JOURNAL OF LUMINESCENCE, 214, DOI: 10.1016/j.jlumin.2019.116540

Eu3+,Tb3+-doped Sr3Al2O6 powder phosphor was synthesized via a precursor route and subjected to a subsequent thermal treatment in reducing atmosphere. Photoluminescence and thermoluminescence properties of Sr3Al2O6:Eu3+/Eu2+,Tb3+ were investigated. The structure and morphology of oxides were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used for the nanocrystals surface composition analysis. X-ray diffraction patterns confirmed the formation of the cubic structure specific to Sr3Al2O6 with space group Pa3 and lattice parameter a = 15.8322 angstrom, while SEM investigations revealed equiaxial, polycrystalline particles, with sizes in the submicronic range, for both Sr3Al2O6:Eu3+,Tb3+ and Sr3Al2O6:Eu3+/Eu2+,Tb3+ samples. The photoluminescence spectra showed the typical f-f luminescence lines of the Tb(3+ )and Eu3+ - ions, accompanied by a broad Eu2+ luminescence band at 510 nm (after calcination in reducing atmosphere). The "after-glow" luminescence signal and the thermoluminescence were assigned to the recombination of close neighbor partners (electron and Eu2+ - hole centers) within the same complex of defects.

54. Particularities of trichloroethylene photocatalytic degradation over crystalline RbLaTa2O7 nanowire bundles grown by solid-state synthesis route

Authors: Raciulete, M; Papa, F; Kawamoto, D; Munteanu, C; Culita, DC; Negrila, C; Atkinson, I; Bratan, V; Pandele-Cusu, J; Balint, I

Published: FEB 2019, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, 7, DOI: 10.1016/j.jece.2018.11.034

This is the first report on synthesis and photocatalytic activity for trichloroethylene (TCE) degradation under simulated solar light over RbLaTa2O7 layered perovskites with predominant nanowire or platelet morphologies. SEM images witnessed that the one step thermal treatment at 1200 degrees C lead to formation of RbLaTa2O7 nanowires with diameter of 80-320 nm and several microns in length associated in bundles and sharp-edged, merged platelets (minor phase). The two-step annealing at 950 degrees C and 1200 degrees C resulted in decrease of wires bundle population and increase in that of platelets merged in facetted particles. The RbLaTa2O7 nanowires are made of by well-aligned atomic rows with preferred orientation toward the c-axis, relatively free of defect. High density of hydroxyl groups on the sample calcined in mild conditions (RbLaTa_01) favors the photo mineralization of TCE. In contrast, the activity of RbLaTa_02 annealed in harsh conditions (950 and 1200 degrees C), poor in surface hydroxyl groups, remained modest. The weak surface basicity directed the reaction mainly to generation of intermediate chlorinated compounds. Pd and Au were supported on RbLaTa2O7 perovskites as an alternative strategy to boost the removal of chlorinated pollutants by combining photocatalytic (mineralization) and catalytic (hydrodechlorination, HDC) processes. The mineralization of TCE to Cl- was drastically hindered in presence of methanol due to quenching of -OH radicals by alcohol. The results suggested that the density of RbLaTa2O7 surface hydroxyl groups is essential for photo mineralization of TCE whereas the surface carbonate is beneficial for the formation of intermediate chlorinated product.

55. Gd3+ co-doping influence on the morphological, up-conversion luminescence and magnetic properties of LiYF4:Yb3+/Er3+ nanocrystals

Authors: Secu, CE; Bartha, C; Matei, E; Negrila, C; Crisan, A; Secu, M

Published: JUL 2019, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 130, 241, DOI: 10.1016/j.jpcs.2019.03.003

The influence of the Gd3+ co-dopant on the structure, morphology and up-conversion luminescence/magnetic properties of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals was investigated and compared to those of Gd-free samples. Electron microscopy has indicated an inhibiting effect of the agglomeration and collapsing process of the nanocrystals compared to the Gd-free powder samples. The surface analysis of nanocrystals have not shown oxygen-metal bonds related to the metal oxidation within the surface nanometric layer. The paramagnetic properties are related to the magnetic moment of the Gd3+ ions. The up-conversion luminescence of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals is about six times stronger than in LiYF4:Yb3+/Er3+ nanocrystals; the enhancement effect is most probably due to the lattice distortion induced by the Gd co-doping.

56. 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.

57. Commercial Hydroxyapatite Powders for Lead Removal from Aqueous Solution

Authors: Negrila, CC; Iconaru, SL; Motelica-Heino, M; Guegan, R; Predoi, G; Barbuceanu, F; Ghita, RV; Petre, CC; Jiga, G; Badea, ML; Prodan, AM; Predoi, D

Published: 2018, 9TH INTERNATIONAL CONFERENCE ON TIMES OF POLYMERS AND COMPOSITES: FROM AEROSPACE TO NANOTECHNOLOGY, 1981, DOI: 10.1063/1.5045983

Nowadays, the advances materials science have created the possibility of using nanomaterials as adsorbents in environmental technologies. This study is focused on the evaluation of C-HAp powders capacity in lead ions removal from contaminated solutions. The C-HAp powders after removal of lead (Pb2+) ions from contaminated water were characterized by X-Ray Photoelectron Spectroscopy (XPS) and Energy Dispersive X-ray analysis (EDX). The presence of lead in the hydroxyapatite powders after removal experiments was observed in the XPS general spectrum and also in the EDX spectra. In addition, the AAS studies revealed that the C-HAp powders possess a high affinity towards lead ions with an effective removal rate of 80% for an initial lead concentration of 20 mg.L-1.

58. Particularities of photocatalysis and formation of reactive oxygen species on insulators and semiconductors: cases of SiO2, TiO2 and their composite SiO2-TiO2

Authors: Anastasescu, C; Negrila, C; Angelescu, DG; Atkinson, I; Anastasescu, M; Spataru, N; Zaharescu, M; Balint, I

Published: NOV 7 2018, CATALYSIS SCIENCE & TECHNOLOGY, 8, 5668, DOI: 10.1039/c8cy00991k

Highly defected tubular SiO2 is found to outperform the activity of TiO2-P25 and the SiO2-TiO2 composite in photocatalytic H-2 generation from methanol-water solution under simulated solar light AM 1.5. The enhanced performances of SiO2 come from the particularities of the reaction mechanism and ROS (reactive oxygen species) generation. The SiO2 exposed to light generates solely O-1(2) (singlet oxygen). The TiO2-P25 produces uniquely large quantities of OH radicals whereas the formation of O-2(-) is evidenced only over SiO2-TiO2, along with small amounts of OH. The TiO2 works as a photocatalyst by intermediation of OH radicals. In contrast, the organic substrate is activated on the surface of SiO2 by the intra-band gap, isolated, surface quantum defects. Distinct reaction mechanisms, involving the participation of photogenerated charges and ROS, are proposed. The material-related ROS production can be of great practical importance in fields such as biology (germ inactivation), medicine (photodynamic therapy by O-1(2)), and synthesis of oxygenated organic compounds of great added value.

59. Surface States- and Field-Effects at GaAs(100) Electrodes in Sodium Dodecyl Sulfate Acid Solution

Authors: Enache, M; Negrila, C; Anastasescu, M; Dobrescu, G; Lazarescu, MF; Lazarescu, V

Published: 2018, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 165, H3017, DOI: 10.1149/2.0031804jes

Sodium dodecyl sulfate (SDS) effects at the electrified p- and n-GaAs(100)/H2SO4 interfaces were investigated by EIS, XPS and AFM. XPS data revealed that under the open circuit conditions, SDS adsorption on GaAs(100) results in a protective overlayer which prevents the further oxidation in air of both types of semiconductor surfaces. The dopant nature is, however, decisive for the way of bonding the surfactant molecule to the surface. At the p-doped substrate, SDS adsorbs mainly at As sites by its hydrocarbon tail and by the anion head to the Ga sites at the n-doped one. Although the surfactant behaves as a dipole under the applied potential control, the dopant type plays a key role in the SDS interaction with GaAs(100) electrodes too. EIS data evidenced that SDS interaction with n-GaAs(100) electrode brings a pronounced decrease of the capacitive contribution of the surface states and a shift of the flatband potential to less negative values, unlike the p-doped one, where no significant change in its electronic properties was observed. These results were rationalized in terms of surface states- and field-effects operating at the electrified interfaces under discussion. (C) The Author(s) 2017. Published by ECS.

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

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

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

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

61. The improvement of SiO2 nanotubes electrochemical behavior by hydrogen atmosphere thermal treatment

Authors: Spataru, N; Anastasescu, C; Radu, MM; Balint, I; Negrila, C; Spataru, T; Fujishima, A

Published: JUN 30 2018, APPLIED SURFACE SCIENCE, 444, 223, DOI: 10.1016/j.apsusc.2018.03.074

Highly defected SiO2 nanotubes (SiO2-NT) were obtained by a simple sol-gel procedure followed by calcination. Boron-doped diamond (BDD) polycrystalline films coated with SiO2-NT were used as working electrodes and, unexpectedly, cyclic voltammetric experiments have shown that the concentration of both positive and negative defects at the surface is high enough to enable redox processes involving positively charged Ru(bpy)(3)(2+/3+) to occur. Conversely, no electrochemical activity was put into evidence for Fe (CN)(6)(3/4) species, most likely as a result of the strong electrostatic repulsion exerted by the negatively charged SiO2 surface. The concentration of surface defects was further increased by a subsequent thermal treatment in a hydrogen atmosphere which, as EIS measurements have shown, significantly promotes Ru (bpy)(3)(2+) anodic oxidation. Digital simulation of the voltammetric responses demonstrated that this treatment does not lead to a similar increase of the number of electron-donor sites. It was also found that methanol anodic oxidation at hydrogenated SiO2-NT-supported platinum results in Tafel slopes of 116-220 mV decade(-1), comparable to those reported for both conventional PtRu and Pt-oxide catalysts. (C) 2018 Elsevier B.V. All rights reserved.

62. Functional properties improvement of Ag-ZnO thin films using Inconel 600 interlayer produced by electron beam evaporation technique

Authors: Lungu, MV; Sobetkii, A; Sobetkii, AA; Patroi, D; Prioteasa, P; Ion, I; Negrila, CC; Chifiriuc, MC

Published: DEC 1 2018, THIN SOLID FILMS, 667, 87, DOI: 10.1016/j.tsf.2018.09.055

500 nm thick silver-zinc oxide (Ag-ZnO) films were grown by electron beam evaporation on 316 L stainless steel (SS) substrate and on 150 nm thick Inconel 600 (IN600) interlayer. The films were annealed in air at 500 degrees C for 1 h. The morphological and structural analyses confirmed smooth, uniform, homogeneous and crack-free surfaces with nanocrystalline grain size for all films. The elemental composition analysis yielded up to 0.6 wt% Ag in Ag-ZnO/IN600 films. The ultraviolet-visible spectroscopy and Raman spectroscopy along with mechanical and electrochemical tests revealed improved optical, scratch resistance and electrochemical properties of Ag-ZnO/IN600 films than Ag-ZnO films. Ag-ZnO/IN600 and Ag-ZnO films exhibited higher antibiofilm activity against Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans pathogens, comparatively with IN600 films and SS substrate. The superior functional properties of Ag-ZnO/IN600 films suggest their potential for practical applications as antimicrobial and robust coatings on SS surface-contacting medical devices with limited exposure.

63. An X-ray photoelectron spectroscopy depth profile study on the InGeNi/(110) cleaved GaAs structure

Authors: Negrila, CC; Lazarescu, MF; Logofatu, C; Ghita, RV; Cotirlan, C

Published: AUG 1 2018, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 82, 66, DOI: 10.1016/j.mssp.2018.02.022

InGeNi ohmic contacts on n-type semi-insulating GaAs(110) cleaved surfaces were fabricated. Cleaving semiconductor single crystal ensures the obtaining of semiconductor surfaces almost ideal in terms of chemical purity and stoichiometry. The chemical depth profile of metallic layer was investigated and revealed through multiple alternating steps of Ar+ etchings and XPS (x-ray photoelectron spectroscopy) measurements. The metallic layers made of alloy of Ge, In and Ni (60 nm Ge, 60 nm In and 10 nm Ni), were obtained by thermal evaporation on cleaved surfaces in a high vacuum facility, followed by a thermal annealing at 430-450 degrees C for 5 min. Twelve etching sessions were required until the metal/semiconductor interface has been reached. A total of 14 etchings steps were performed during the experiment, a layer with a thickness of 140 nm being removed from the surface. The atomic concentrations of the constituent chemical elements were determined. In3d, In4d, Ga3d, Ga2p, As3d, As2p, Ni2p(3/2), Ge3d, O1s and C1s spectral lines were recorded and chemical bonds within the layer were analyzed from the fittings. The formation of InxGa1-xAs type compounds and of an intermediate semiconductor layer rich in Ge atoms at the interface was highlighted. X-ray detectors InGeNi/GaAs/Al and InGeNi/GaAs/Ti were fabricated with ohmic contacts based on this contacting scheme and Schottky interfaces prepared also by evaporation on cleaved edges. Electrical characteristics have been investigated and key diode parameters determined - ideality factor, Schottky barrier height, series resistance. Detection capabilities of these devices were studied in an x-rays flux, provided by a Co anode x-ray source.

64. Influence of Mn content on the catalytic properties of Cu(Mn)-Zn-Mg-Al mixed oxides derived from LDH precursors in the total oxidation of methane

Authors: Raciulete, M; Layrac, G; Papa, F; Negrila, C; Tichit, D; Marcu, IC

Published: MAY 15 2018, CATALYSIS TODAY, 306, 286, DOI: 10.1016/j.cattod.2017.01.013

Cu-(Mn)-Zn-Mg-Al mixed oxides with Cu/Zn atomic ratio of 1 and different Mn contents were synthesized by thermal decomposition of layered double hydroxides (LDHs) precursors. They were characterized using X-ray diffraction, textural measurements, EDX, TEM, H-2-TPR and XPS techniques, and their catalytic properties in the total oxidation of methane were evaluated. The precursors consisted in nitrate-interlayered multicationic LDH phase with additional Mn3O4 side phase for Mn-containing systems. Their thermal decomposition resulted in complex mixed oxides containing periclase-like, CuO and different spinel (Cu1.5Mn1.5O4, CuMn2O4, and MnAl2O4) phases. XPS analysis confirmed the existence of copper and manganese with different valence states in the Cu,Mn-containing mixed oxides. The catalytic activity expressed as the intrinsic rate of CH4 conversion increased by adding Mn to the CuZnMgAl mixed oxide calcined at 650 degrees C and by increasing its content. The intrinsic activity also strongly increased when the calcination temperature increased from 650 to 800 degrees C. The increased activity was correlated to enhanced catalyst reducibility due to the favorable Cu-Mn interaction. Among the different catalytic active phases, i.e. CuO, Cu1.5Mn1.5O4 and CuMn2O4, the Cu1.5Mn1.5O4 spinel seems to be the most active one. (C) 2017 Elsevier B.V. All rights reserved.

65. Development of Zinc-Doped Hydroxyapatite by Sol-Gel Method for Medical Applications

Authors: Negrila, CC; Predoi, MV; Iconaru, SL; Predoi, D

Published: NOV 2018, MOLECULES, 23, DOI: 10.3390/molecules23112986

Zinc- (Zn) doped hydroxyapatite (HAp) were prepared by sol-gel method. Zinc-doped hydroxyapatite (ZnHAp) and HAp were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Rietveld analysis revealed that the HAp and 7ZnHAp powders obtained by sol-gel method have a monophasic hydroxyapatite structure belonging to the P6(3/m) spatial group. The results obtained from the ultrasound characterization of HAp and ZnHAp are also presented in this study. The effect of zinc concentration on properties that were deduced from ultrasonic measurements are studied in the case of a significant zinc concentration (x(Zn) = 0.07). From the values of the ultrasonic waves velocities were determined by the pairs of elastic coefficients of the suspensions (Young modulus E, Poisson coefficient nu), which have proven to be similar to those determined by other authors.

66. ANALYSIS of Pdge-BASED CONTACT on N-Gasb

Authors: Ghita, RV; Negrila, CC; Predoi, D; Trusca, R

Published: 2018, 7TH INTERNATIONAL CONFERENCE ON STRUCTURAL ANALYSIS OF ADVANCED MATERIALS (ICSAAM 2017), 1932, DOI: 10.1063/1.5024167

Pd-Ge based ohmic contacts on III-V semiconductor e.g.Pd-Ge on n-GaAs are viewed as a viable alternative to low contact resistance metallization. As it was remarked [11, together with the device dimensions decrease, the AuGeNi metallization system becomes inadequate for shallow-junction devices. This characteristic is related to the formation of a low melting point beta- AuGa phase that leads to a poor contact thermal stability. Gallium Antimonide is anIII-V semiconductor compound that can be used in a photovoltaic convertor of GaAs/GaSb tandem stack With a predicted efficiency of 30%. Reduced series resistance on GaSb cells can be achieved by the improving of contact metallization properties. The present study is dedicated to the preparation conditions and structural analyzing of PdGe based contacts on n-GaSb, namely: Pd/Au/Ge. There are presented the depth profiling for PdGe metallization obtained from XPS measurements, and morphologic studies arisen from SEM technique and AFM technique.

67. Photocatalytic activity of wool fabrics deposited at low temperature with ZnO or TiO2 nanoparticles: Methylene blue degradation as a test reaction

Authors: Frunza, L; Diamandescu, L; Zgura, I; Frunza, S; Ganea, CP; Negrila, CC; Enculescu, M; Birzu, M

Published: MAY 15 2018, CATALYSIS TODAY, 306, 259, DOI: 10.1016/j.cattod.2017.02.044

Different amounts of TiO2 and ZnO particles were deposited upon wool fabrics, which are among the less studied textiles. The materials were get from industry or were home made. Model samples for these oxide deposition and properties were also considered. Either sputtering or chemical sol-gel/electro less technique was respectively applied. The coated samples were then characterized structurally and morphologically, by XRD, SEM and XPS and were checked for photocatalytic properties. Both UV and vis light beams were used for irradiation. The photocatalytic experiments were performed by photodegradation of methylene blue in the PCC2 checker apparatus. The fabrics were firstly impregnated with the dye solution and then dried: self cleaning of the wool fabric samples took in fact place. Reflectance data in the visible spectral range of highest absorption band served for direct analysis of MB degradation. The photocatalytic properties of the coated fabrics increased much in comparison with the raw materials. The photocatalytic decolorization of methylene blue follows up a simple apparently first order kinetic equation in many studied cases. Thus it was demonstrated that MB decolorization can serve as a test reaction at least for self cleaning of fabrics. (C) 2017 Elsevier B.V. All rights reserved.

68. Investigation of sol-gel derived BaCl2:Eu2+ luminescent nanophosphor and the corresponding PVP@BaCl2:Eu2+ polymer nanocomposite

Authors: Secu, CE; Negrila, C; Secu, M

Published: AUG 1 2018, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 51, DOI: 10.1088/1361-6463/aace7c

We have prepared Eu2+ (1%) doped BaCl2 nanopowders by using a hybrid sol-gel/thermal decomposition route using barium acetate and trichloracetic acid as in situ chlorination agent. Structural and thermal analysis data have shown that orthorhombic BaCl2 phase crystallization occurs at 260 degrees C. BaCl2:Eu2+ nanocrystals of about 100-200 nm in size were produced after annealing (in air) at 500 degrees C and they displayed Eu2+ d -> f type luminescence at 396 nm. X-ray photoelectron spectroscopy indicated the presence of both Eu2+, Eu3+ ions species and a BaO passivating layer at the surface of the nanocrystals. A polymer nanocomposite (PVP@BaCl2:Eu2+) was also processed and its optical response under x-ray irradiation was found to be similar to that of the nanopowder. X-ray excited luminescence showed Eu2+ luminescence at 396 nm, whereas the thermoluminescence peak at 130 degrees C was assigned to the F(Cl)-center recombination with Eu2+ related hole centers.

69. Combined Electrochemical Impedance Spectroscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy study of the distinct behavior of L-cysteine-thiolate formed at p- and n-GaAs(100) electrodes in Sodium Dodecyl Sulfate solution

Authors: Lazarescu, V; Enache, M; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF

Published: JAN 20 2017, ELECTROCHIMICA ACTA, 225, 558, DOI: 10.1016/j.electacta.2016.12.156

Electrochemical impedance spectroscopy (EIS), X-ray spectroscopy (XPS), and atomic force microscopy (AFM) have been used to investigate the effects of the sodium dodecyl sulfate (SDS) interaction with the L-cysteine-thiolate covered p- and n-GaAs(100) electrodes in H2SO4 solution. The potential-induced reversible proton transfer found to occur within the L-cysteine-thiolate layer in the simple acid solution during the cathodic as well as the anodic potential scans at the p-doped semiconductor electrode and only in the anodic scan at the n-doped one is suppressed in both cases. XPS data revealed that the anionic surfactant has a complex interaction with the L-cysteine-thiolate covered GaAs(100) electrodes, which implicates both electrostatic and chemical forces. The SO42 head group interacts electrostatically with the NH3+ group of the cysteine-thiolate but it is also chemically involved in a chemisorption bond with the available Ga atoms. The amount of Ga-bound SDS species is much more pronounced at the L-cysteine-thiolate/p-GaAs(100) than at the L-cysteine thiolate/n-doped GaAs(100) electrodes meaning that cysteine-thiolate is mainly formed at As sites in the first case and at Ga sites in the latter one. This outcome strengthens the previous conclusions concerning the role of the dopant in determining the bonding way of the L-cysteine on GaAs(100) surfaces. (C) 2016 Elsevier Ltd. All rights reserved.

70. 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.

71. Chalcogenide thin films deposited by rfMS technique using a single quaternary target

Authors: Prepelita, P; Stavarache, I; Negrila, C; Garoi, F; Craciun, V

Published: DEC 1 2017, APPLIED SURFACE SCIENCE, 424, 427, DOI: 10.1016/j.apsusc.2016.11.071

Thin films of chalcogenide, Cu(In, Ga) Se-2 have been obtained using a single quaternary target by radio frequency magnetron sputtering method, with thickness in the range 750 nm to 1200 nm. X-ray photoelectron spectroscopy investigations showed, that the composition of Cu(In, Ga) Se-2 thin films was very similar to that of the used target CuIn0.75Ga0.25Se2. Identification of the chemical composition of Cu(In, Ga) Se-2 thin films by XPS performed in high vacuum, emphasized that the samples exhibit surface features suitable to be integrated into the structure of solar cells. Atomic Force Microscopy and Scanning Electron Microscopy investigations showed that surface morphology was influenced by the increase in thickness of the Cu(In, Ga) Se-2 layer. From X-Ray Diffraction investigations it was found that all films were polycrystalline, having a tetragonal lattice with a preferential orientation along the (112) direction. The optical reflectance as a function of wavelength was measured for the studied samples. The increase in thickness of the Cu(In, Ga) Se-2 absorber determined a decrease of its optical bandgap value from 1.53 eV to 1.44 eV. The results presented in this paper showed an excellent alternative of obtaining Cu(In, Ga) Se-2 compound thin films from a single target. (C) 2016 Elsevier B.V. All rights reserved.

72. Photocatalytic abatement of trichlorethylene over Au and Pd-Au supported on TiO2 by combined photomineralization/hydrodechlorination reactions under simulated solar irradiation

Authors: State, R; Papa, F; Tabakova, T; Atkinson, I; Negrila, C; Balint, I

Published: FEB 2017, JOURNAL OF CATALYSIS, 346, 108, DOI: 10.1016/j.jcat.2016.11.032

The present work investigates the photocatalytical abatement of trichlorethylene (TCE) under simulated solar irradiation (AM 1.5). The employed catalytic materials, Au and Pd-Au nanoparticles supported on TiO2, were prepared by incipient wetness and by deposition-precipitation methods. It is found out that TCE is converted efficiently (>80%) to CI- and CO2 over all scrutinized catalysts. Typically, the metal addition enhances to some extent the photooxidation activity of TiO2 via photogenerated center dot OH radicals, electrons, and holes. The photocatalytic abatement of TCE over the same catalytic materials was examined in the presence of small amount of methanol. The idea was to convert TCE to Cl- and C-2 (ethane and ethylene) over Au and Pd-Au/TiO2 catalysts by the H-2 generated photocatalytically in situ. The experimental results evidenced that, over Pd-Au/TiO2 catalysts, hydrodechlorination (HDC) and photomineralization reactions of TCE occurs simultaneously. In contrast, Au/TiO2 is inactive to catalyze the hydrogenation of TCE. The results of TCE abatement by combined photooxidation/HDC reactions in presence of methanol are corroborated with H-2 photocatalytic generation results, over the same catalytic materials, from water/methanol mixture. A reaction mechanism is advanced in light of experimental results. The photo generated center dot OH radicals, electrons, and holes participate in a complex reaction pathway to formation of oxygenated organic intermediates, Cl-, CO2, and H-2. (C) 2016 Elsevier Inc. All rights reserved.

73. Defect-related light absorption, photoluminiscence and photocatalytic activity of SiO2 with tubular morphology

Authors: Anastasescu, C; Zaharescu, M; Angelescu, D; Munteanu, C; Bratan, V; Spataru, T; Negrila, C; Spataru, N; Balint, I

Published: JAN 2017, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 159, 335, DOI: 10.1016/j.solmat.2016.09.032

The research describes the synthesis, optical, photocatalytic, electrochemical and photoelectrocatalytical properties of highly defected, low surface area, tubular SiO2. High surface density of light-absorbing defects is obtained by conducting the synthesis at low temperature (0 degrees C) and by optimizing the ratios between reactants. The calcined tubular SiO2 is characterized by intense and broad absorption band centered at approximate to 320 nm, spanning from deep UV to green. The formation of Si3+ surface defects by calcination is accompanied by a substantial intensification of light absorbing characteristics. The annealing leads also to appearance of intense photoluminescence bands centered at around 433 and 533 nm for excitation wavelengths 320-380 nm. The photocatalytic generation of H-2 and CO2 from water-methanol mixture under solar (AM 1.5) and visible (lambda > 390 nm) irradiation is performed to probe the capability of light-absorbing defects of SiO2 to work as active sites and to gather indirect information on nature of active sites. The electrochemical and photoelectrochemical activity of tubular SiO2 are highlighted by employing [Ru(bpy)(3)]Cl-2 complex as electron transfer witness. According to our results, highly defected nanotubular SiO2 exhibit uncommon optical, light harvesting, electronic and electrochemical properties with great potential for practical applications in numerous fields. (C) 2016 Elsevier B.V. All rights reserved.

74. Mechanical, Corrosion and Biological Properties of Room-Temperature Sputtered Aluminum Nitride Films with Dissimilar Nanostructure

Authors: Besleaga, C; Dumitru, V; Trinca, LM; Popa, AC; Negrila, CC; Kolodziejczyk, L; Luculescu, CR; Ionescu, GC; Ripeanu, RG; Vladescu, A; Stan, GE

Published: NOV 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7110394

Aluminum Nitride (AlN) has been long time being regarded as highly interesting material for developing sensing applications (including biosensors and implantable sensors). AlN, due to its appealing electronic properties, is envisaged lately to serve as a multi-functional biosensing platform. Although generally exploited for its intrinsic piezoelectricity, its surface morphology and mechanical performance (elastic modulus, hardness, wear, scratch and tensile resistance to delamination, adherence to the substrate), corrosion resistance and cytocompatibility are also essential features for high performance sustainable biosensor devices. However, information about AlN suitability for such applications is rather scarce or at best scattered and incomplete. Here, we aim to deliver a comprehensive evaluation of the morpho-structural, compositional, mechanical, electrochemical and biological properties of reactive radio-frequency magnetron sputtered AlN nanostructured thin films with various degrees of c-axis texturing, deposited at a low temperature (similar to 50 degrees C) on Si (100) substrates. The inter-conditionality elicited between the base pressure level attained in the reactor chamber and crystalline quality of AlN films is highlighted. The potential suitability of nanostructured AlN (in form of thin films) for the realization of various type of sensors (with emphasis on bio-sensors) is thoroughly probed, thus unveiling its advantages and limitations, as well as suggesting paths to safely exploit the remarkable prospects of this type of materials.

75. XPS Analysis of AuGeNi/Cleaved GaAs(110) Interface

Authors: Negrila, CC; Lazarescu, MF; Logofatu, C; Cotirlan, C; Ghita, RV; Frumosu, F; Trupina, L

Published: 2016, JOURNAL OF NANOMATERIALS, 2016, DOI: 10.1155/2016/7574526

The depth composition of the thin layer alloy, AuGeNi, devoted to acting as an ohmic contact on n-GaAs(110) has been investigated by in situ XPS combined with Argon ion sputtering techniques. The fresh cleaved surfaces, supposed to be free of oxygen, were usually deposited with a 200nm metallic layer in high vacuum conditions (better than 10(-7) torr), by thermal evaporation, and annealed at a 430-450 degrees Celsius temperature for 5 minutes. About 18 sessions of ion Ar surfaces etching and intermediate XPS measurements were performed in order to reveal the border of the metal/semiconductor interface. The atomic concentrations of the chemical elements have been approximated. Au4f, Ga3d, Ga2p, As3d, As2p, Ni2p(3/2), Ge3d, O1s, and C1s spectral lines were recorded. The Au, Ge, and Ni have a homogenous distribution while Ga and As tend to diffuse to the surface. Oxygen is present in the first layers of the surface while carbon completely disappears after the second etching step. The existence of an Au-Ga alloy was detected and XPS spectra show only metal Ni and Ge within the layer and at the interface. We tried to perform a study about the depth chemical composition profile analysis of AuGeNi layer on cleaved n-GaAs(110) by X-Ray Photoelectron Spectroscopy (XPS) technique.

76. Aspects of native oxides etching on n-GaSb(100) surface

Authors: Cotirlan, C; Ghita, RV; Negrila, CC; Logofatu, C; Frumosu, F; Lungu, GA

Published: FEB 15 2016, APPLIED SURFACE SCIENCE, 363, DOI: 10.1016/j.apsusc.2015.11.181

Gallium antimonide (GaSb) is the basis of the most photovoltaic and thermophotovoltaic (TPV) systems and its innovative technological aspects based on modern ultra-high vacuum techniques are in trend for device achievement. The real surface of GaSb is modified by technological processes that can conduce to problems related to the reproducible control of its surface properties. The GaSb surface is reactive in atmosphere due to oxygen presence and exhibits a native oxide layer. The evolution of native oxides during the ion sputtering, chemical etching and thermal annealing processes for preparing the surface is presented in detailed way. Ratios of surface constituents are obtained by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS). Moreover, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM) and Low-Energy Electron Diffraction (LEED) are used for characterization. The surface stoichiometry is changed using a specific etchant (e.g. citric acid) at different etching time and is analyzed by ARXPS, SEM, EDS and AFM methods. The experimental results provide useful information regarding surface native oxides characteristics on n-GaSb(100) to be taken into account for development of low resistance contacts for TPV devices based on GaSb alloy. (C) 2015 Elsevier B.V. All rights reserved.

77. Combined ab initio and XPS Investigations of the Electronic Interactions of L-Cysteine Adsorbed on GaAs(100)

Authors: Juarez, MF; Toader, AM; Negrila, C; Santos, E; Lazarescu, V

Published: AUG 16 2016, CHEMISTRYSELECT, 1, 3634, DOI: 10.1002/slct.201600589

The adsorption of L-cysteine from ethanol solutions on GaAs(1 0 0) surfaces has been studied by XPS and density-functional theory (DFT). XPS data reveal that the formation of the adsorbate involves preferentially the As-sites for p-GaAs(1 0 0) and the Ga-sites for n-GaAs(1 0 0). The adsorbed species show different orientations of the functional groups to the surface for the different substrates. DFT calculations performed for both Ga-dimers and As-dimers terminated surfaces show that the adsorption is energetically favourable on both substrates. However, the adsorption energy is more negative on top of Ga-atoms. Here an important contribution for the stabilization of the adsorbate is the interaction of the functional groups with the surface. The parallel orientation found for the Ga-bound species by DFT calculations is in good agreement with the shift in the binding energy of the NH2/NH3+ species observed by XPS analysis.

78. Role of the dithiolate backbone on the passivation of p-GaAs(111)B surface

Authors: Preda, L; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, V

Published: JUN 15 2016, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 771, 63, DOI: 10.1016/j.jelechem.2016.03.046

Effects of the self-assembled layers of biphenyl 4,4'-dithiol (BPDT) and 1,8-octanedithiol (ODT) on the chemical and electronic properties of p-doped GaAs (111)-As terminated substrate, (p-GaAs(111)B), were investigated in order to evidence whether the hydrocarbon moiety plays a role in tailoring the semiconductor surface properties. The electrochemical properties of the BPDT and ODT coated p-GaAs(111)B substrates were studied by Electrochemical Impedance Spectroscopy (EIS). The structural and chemical changes caused by the dithiolate layers formed on p-GaAs(111)B substrates were monitored by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) investigations, respectively. The XPS data showed that BPDT and ODT bind to pGaAs(111)B via the thiol group. The ODT layer provides better protection against the further oxidation in air of p-GaAs(111)B substrate compared to the BPDT layer. The EIS investigations are in good agreement with XPS results, pointing to better insulating properties of the ODT layer compared to the BPDT layer in the electron transfer at the electrode/solution interface. The results evidenced that backbone plays an important role in tailoring the properties of p-GaAs(111)B substrate. (C) 2016 Elsevier B.V. All rights reserved.

79. INFRARED AND X-RAY PHOTOELECTRON SPECTROSCOPY IN SURFACE CHARACTERIZATION OF POLYDIMETHYLSILOXANE THIN FILMS GENERATED ON METALLIC SUBSTRATES IN MULTIPOINTS TO PLANE CORONA DISCHARGES

Authors: Groza, A; Surmeian, A; Diplasu, C; Negrila, C; Mihalcea, B; Ganciu, M

Published: 2016, ROMANIAN JOURNAL OF PHYSICS, 61, 656, DOI:

By coupling two spectral techniques, namely, X-ray photoelectron and specular reflection infrared spectroscopy at high reflection angles, we identified, in this paper,. the formation of SiO2 respectively SiOx (1 < x < 2) structures on the surface of polydimethylsiloxane thin films. These layers have been obtained as a result of placing a thin liquid film precursor on a germanium substrate under corona charge injection in multipoints to plane electrodes configuration in air at atmospheric pressure for 2 hours.

80. Influence of Single-Walled Carbon Nanotubes Enriched in Semiconducting and Metallic Tubes on the Vibrational and Photoluminescence Properties of Poly(para-phenylenevinylene)

Authors: Baibarac, M; Baltog, I; Ilie, M; Humbert, B; Lefrant, S; Negrila, C

Published: MAR 17 2016, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 5705, DOI: 10.1021/acs.jpcc.5b11198

A new synthesis method based on the electrochemical reduction of alpha,alpha,alpha',alpha'-tetrabromo-p-xylene in the presence of single-walled carbon nanotubes (SWNTs) is used to obtain composites of carbon nanotubes (CNTs) functionalized with poly(para-phenyl-enevinylene) (PPV). To separate the effects of metallic and semiconducting CNTs on their interaction with PPV, the experiments are carried out with SWNTs enriched in semiconducting (S, 99%) and metallic (M, 98%) tubes. Significant changes in the relative intensity and shift of the radial breathing vibrational mode are reported in the Raman spectra of the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) entities and SWNTs enriched in M tubes (98%) that result from the electrofunctionalization with PPV. This different behavior originates in the noncovalent and covalent functionalization of SWNTs enriched in M and S SWNTs tubes with PPV, respectively. A gradual decrease in the absorption of the infrared (IR) bands of PPV situated in the spectral range of 750-1000 cm(-1) as a result of the increase of the polymer weight on the blank Au support is reported. The electrofunctionalization of the as-prepared SWNTs induces position changes of the PPV IR absorption bands. In the presence of S-enriched SWNTs, a significant increase in the absorbance of the two IR bands peaked at 1452 and 1471 cm(-1), which are assigned to the vibrational modes of the phenyl ring stretching and the quinoid structure of the PPV, respectively, is reported. This results from the covalent bonding of the PPV macromolecular chains onto the surface of the SWNTs enriched in S tubes. Our results also demonstrate that the photoluminescence quenching effect reported for the PPV/SWNTs composites is due to the metallic nanotubes.

81. Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere

Authors: Trupina, L; Nedelcu, L; Negrila, C; Banciu, MG; Huitema, L; Crunteanu, A; Rammal, M; Ghalem, A

Published: SEP 2016, JOURNAL OF MATERIALS SCIENCE, 51, 8717, DOI: 10.1007/s10853-016-0131-1

The growth and thermal stability of textured iridium thin films used as bottom electrode in electronic devices based on ferroelectric materials were investigated. The thin films were grown using the dc magnetron sputtering technique. The Ir layers directly deposited on SiO2/Si substrates present a mixed (111) and (200) orientations, while the films grown on Ti seed layers exhibit a strong preferred (111) orientation favoured by good matching with the titanium lattice. The substrate temperature during the growth of iridium/titanium stack has a significant effect on the surface morphology of the iridium layer and its thermal stability. The as-grown surface of 20-nm-thick Ir films is smooth, having a root-mean-square (rms) roughness of 0.7 nm. After thermal annealing the Ir film shows an increased surface roughness due to the formation of agglomerations. The change in the surface morphology of the Ir layer is due to titanium diffusion and its oxidation. Thicker and better crystallised iridium thin films annealed in oxygen atmosphere at 700 A degrees C show a good thermal stability with only a slight modification of the surface morphology. Within the limits of experimental error, there is no change in the electrical resistivity before and after thermal annealing. The rms roughness has not varied significantly and the XPS investigation shows no traces of titanium oxide on iridium surface. Ir/Ti stack deposited under the optimum conditions could be successfully used as electrode in devices based on oxide thin films.

82. Field - dipole interactions in L-cysteine-thiolate self assembled at p- and n-GaAs(100) electrodes

Authors: Lazarescu, V; Toader, AM; Enache, M; Preda, L; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF

Published: SEP 10 2015, ELECTROCHIMICA ACTA, 176, 124, DOI: 10.1016/j.electacta.2015.06.121

L-cysteine-thiolate monolayers spontaneously self-assembled on p- and n-GaAs(100) electrodes have been investigated by electrochemical impedance spectroscopy in H2SO4 solutions. On p-doped samples a potential-induced reversible proton transfer occurs within the L-cysteine-thiolate layer during both forward and backward potential scans; in contrast, on n-doped samples it is observed only in the reverse scan. The XPS data and the fractal analysis of the AFM images point to the field - dipole interactions operating distinctively in the L-cysteine-thiolate layer formed at p-and n-doped semiconducting substrates as the origin of the observed difference. The interaction of this small but highly polar molecule with the electrostatic field driven by the diffuse distribution of the excess charge in the semiconductor subsurface region both in equilibrium and under polarization conditions turned out to play a key role in determining the optimal orientation of the two polar groups. The latter one seems to be a prerequisite for the potential-induced internal proton transfer. (C) 2015 Elsevier Ltd. All rights reserved.

83. Titanium dioxide layer deposited at low temperature upon polyester fabrics

Authors: Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Ganea, CP; Negrila, CC; Diamandescu, L

Published: JUL-AUG 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1063, DOI:

TiO2 deposition by sputtering or sol-gel techniques was applied onto less thermal stable polyester textiles and onto a related poly(lactic acid) material. The temperature of deposition and of the further treatment was low enough as allowed by the support nature. Structural and spectroscopic characterization of the raw and coated samples has been performed. TiO2 coated particles are amorphous as indicated by X-ray diffraction and scanning electron microscopy. Sputtered layers consist in aggregates randomly distributed on the substrate while the sol gel layers show a uniform coverage of nanoparticles having a mosaic-like structure. The morphology of the sputtered layers depends on the deposition pressure as well. The loading degree estimated on the basis of the thermogravimetric data is rather low (ca. 2%), but the fabric properties are much influenced by the deposition. Photocatalytic activity also present on the coated surfaces was evaluated in the methylene blue degradation. TiO2 layer is quite adherent as checked by an ultra-sonication method.

84. Chemically assembled light harvesting CuOx-TiO2 p-n heterostructures

Authors: Anastasescu, C; Spataru, N; Culita, D; Atkinson, I; Spataru, T; Bratan, V; Munteanu, C; Anastasescu, M; Negrila, C; Balint, I

Published: DEC 1 2015, CHEMICAL ENGINEERING JOURNAL, 281, 311, DOI: 10.1016/j.cej.2015.06.098

CuOx nanorods grown by calcination on a Cu plate and TiO2 successive layers were assembled by chemical means to obtain a broad band light captor. The synthesis of composite with complex architecture aimed at maximization of light absorption and at improvement of electron-holes separation of via the multiple n-p heterojunctions created at TiO2-CuOx boundaries, formed mostly by filling the pore network composite material with CuOx. Au nanoparticles were embedded into TiO2 matrix to enhance the light harvesting ability in visible domain via surface plasmon resonance (SPR) phenomenon and to help the photo-generated charge separation through the formation of Schottky barriers. Dual p-n semiconducting character of the composite was clearly evidenced by photoelectrochemical measurements. The composite material exhibited photoresponse even at wavelengths higher than 420 nm (in visible domain), both in cathodic and anodic regions. The enhanced light adsorption characteristics, the advancement in synthesis procedure of CuOx-Au_TiO2 composite material provide rationale for further development of novel light captor composites for photoenergy conversion. Other applications such electronics and gas sensors are envisaged. (C) 2015 Elsevier B.V. All rights reserved.

85. Antimicrobial Activity Evaluation on Silver Doped Hydroxyapatite/Polydimethylsiloxane Composite Layer

Authors: Ciobanu, CS; Groza, A; Iconaru, SL; Popa, CL; Chapon, P; Chifiriuc, MC; Hristu, R; Stanciu, GA; Negrila, CC; Ghita, RV; Ganciu, M; Predoi, D

Published: 2015, BIOMED RESEARCH INTERNATIONAL, 2015, DOI: 10.1155/2015/926513

The goal of this study was the preparation, physicochemical characterization, and microbiological evaluation of novel hydroxyapatite doped with silver/polydimethylsiloxane (Ag:HAp-PDMS) composite layers. In the first stage, the deposition of polydimethylsiloxane (PDMS) polymer layer on commercially pure Si disks has been produced in atmospheric pressure corona discharges. Finally, the new silver doped hydroxyapatite/polydimethylsiloxane composite layer has been obtained by the thermal evaporation technique. The Ag: HAp-PDMS composite layers were characterized by various techniques, such as Scanning Electron Microscopy (SEM), Glow Discharge Optical Emission Spectroscopy (GDOES), and X-ray photoelectron spectroscopy (XPS). The antimicrobial activity of the Ag:HAp-PDMS composite layer was assessed against Candida albicans ATCC 10231 (ATCC-American Type Culture Collection) by culture based and confirmed by SEM and Confocal Laser Scanning Microscopy (CLSM) methods. This is the first study reporting the antimicrobial effect of the Ag: HAp-PDMS composite layer, which proved to be active against Candida albicans biofilm embedded cells.

86. Impact of particle size and metal-support interaction on denitration behavior of well-defined Pt-Cu nanoparticles

Authors: Miyazaki, A; Matsuda, K; Papa, F; Scurtu, M; Negrila, C; Dobrescu, G; Balint, I

Published: 2015, CATALYSIS SCIENCE & TECHNOLOGY, 5, 503, DOI: 10.1039/c4cy00929k

Well-dispersed Pt-Cu nanoparticles with two average sizes were synthesized: small (approximate to 1.6 nm) and large (approximate to 4.8 nm), respectively. The effects of size and support on the catalytic behavior of the nanoparticles for denitration reaction were analyzed. Both the unsupported and alumina-supported nanoparticles of smaller average size (1.6 nm) were very active, completely converting NO3- and NO2- (an intermediate reaction product) to N-2 and NH4+. They were also more selective of N-2 compared to the larger particles. The effects of particle size and alumina support on the denitration rate constants were analyzed in detail. The kinetic investigation indicates that the catalytic behavior is strongly related to the size of Pt-Cu nanoparticles as well as to the metal-support interaction. Generally, the larger nanoparticles proved to be less active, but on the other hand, they are less influenced by the support than the smaller ones. The metal-support interaction for bimetallic nanoparticles with smaller average size proved to be a key factor both for nitrate and nitrite reduction. Consideration of the reaction mechanism is made in light of the experimental results.

87. Systematic investigation and in vitro biocompatibility studies on mesoporous europium doped hydroxyapatite

Authors: Popa, CL; Ciobanu, CS; Iconaru, SL; Stan, M; Dinischiotu, A; Negrila, CC; Motelica-Heino, M; Guegan, R; Predoi, D

Published: OCT 2014, CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 12, 1046, DOI: 10.2478/s11532-014-0554-y

This paper reports the systematic investigation of europium doped hydroxyapatite (Eu:HAp). A set of complementary techniques, namely Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) technique were used towards attaining a detailed understanding of Eu:HAp. The XPS analysis confirmed the substitution of Ca ions by Eu ions in the Eu:HAp samples. Secondly, Eu:HAp and pure HAp present type IV isotherms with a hysteresis loop at a relative pressure (P/P-0) between 0.4 and 1.0, indicating the presence of mesopores. Finally, the in vitro biological effects of Eu:HAp nanoparticles were evaluated by focusing on the F-actin filament pattern and heat shock proteins (Hsp) expression in HEK293 human kidney cell line. Fluorescence microscopy studies of the actin protein revealed no changes of the immunolabelling profile in the renal cells cultured in the presence of Eu:HAp nanoparticles. Hsp60, Hsp70 and Hsp90 expressions measured by Western blot analysis were not affected after 24 and 48 hours exposure. Taken together, these results confirmed the lack of toxicity and the biocompatibility of the Eu:HAp nanoparticles. Consequently, the possibility of using these nanoparticles for medical purposes without affecting the renal function can be envisaged.

88. The evanescent-wave cavity ring-down spectroscopy technique applied to the investigation of thermally grown oxides on Si(100)

Authors: Cotirlan-Simioniuc, C; Ghita, RV; Negrila, CC; Logofatu, C

Published: NOV 2014, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 117, 1365, DOI: 10.1007/s00339-014-8556-3

We report about the contribution of thermally grown SiOx overlayer on the SiOx/Si interface (with oxidation states Sin+, where n = 1, 2, 3, 4) to the optical losses of a resonant spectroscopic cavity. The experiments on Si oxide thin films were performed in evanescent wave for Si samples in contact with a total internal reflection surface of a BK7 prism. The evanescent field can be exploited to investigate properties and processes such as the absorption of thin film or solid/air interface reactions. The results show that the oxide overlayer thickness grows with the thermal exposure time and is limited after more than 7 h of treatment. Transmission electron microscopy has been used for the native oxide thickness measurement and angle-resolved X-ray photoelectron spectroscopy used to determine the thermal oxide thickness. A change of absorption coefficient Delta alpha in the range 100-200 cm(-1) is obtained by evanescent-wave cavity ring-down spectroscopy (EW-CRDS) for thermal silicon oxide overlayer, in agreement with the general trend from literature. The evaluation from the EW-CRDS experiments presents the used setup as a competitive method for measuring the absorption properties of thin overlayer.

89. Supported Pd-Cu Nanoparticles for Water Phase Reduction of Nitrates. Influence of the Support and of the pH Conditions

Authors: Papa, F; Balint, I; Negrila, C; Olaru, EA; Zgura, I; Bradu, C

Published: DEC 10 2014, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 53, 19103, DOI: 10.1021/ie503070f

PdCu nanoparticles were synthesized by the alkaline polyol method and further supported on alumina or titania. The nanoparticles show a crystalline Pd core and a shell rich in amorphous copper as was put in evidence by complex characterization methods (X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and CO chemisorption). The performances of as-prepared catalysts in the water phase reduction of nitrate were assessed in comparison with catalysts obtained by impregnation. Supported nanoparticle catalysts show a high activity in the reduction of nitrates, better than the impregnated catalysts. The importance of the support choice was discussed. The catalyst based on PdCu nanoparticles supported on titania (PCT-np) is the most active, selective, and stable among those investigated. Also, the influence of pH conditions on the PCT-np catalyst performances was emphasized.

90. Electrochemical impedance spectroscopy investigations on the L-cysteine-thiolate self-assembled monolayers formed at p-GaAs(100) electrodes

Authors: Lazarescu, V; Enache, M; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF

Published: JUN 10 2014, ELECTROCHIMICA ACTA, 131, 51, DOI: 10.1016/j.electacta.2013.11.103

Electrochemical impedance spectroscopy investigations carried out in solutions with different pH brought evidence that the monolayers of L-cysteine-thiolate self-assembled on GaAs (hid) electrodes exert a complex molecular control over their electrochemical behavior. The analysis of the impedance spectra coupled with that of the XPS data and the AFM images taken before and after the EIS measurements reveled that both pH and applied potential brings significant changes at the electrified interface. The most important effect of pH is the conformational change of the L-cysteine-thiolate molecule observed at pH 11 that allows the interaction of the carboxyl group with the substrate atoms. A similar conformational change occurs at pH 5.5 but only under the applied potential control, being just a consequence of another major effect of the applied electric field. This is the H+ transfer inside the L-cysteine-thiolate film, an electric field driven process but pH dependent, which results in significant charge diminution both in the organic overlayer and in the semiconductor depletion region. (C) 2013 Elsevier Ltd. All rights reserved.

91. Generation of Porous Alumina Layers in a Polydimethylsiloxane/Hydrogen Peroxide Medium on Aluminum Substrate in Corona Discharges

Authors: Groza, A; Surmeian, A; Diplasu, C; Luculescu, C; Negrila, C; Ganciu, M

Published: 2014, JOURNAL OF NANOMATERIALS, 2014, DOI: 10.1155/2014/578720

The porous alumina (Al2O3) layer obtained at the interface between polydimethylsiloxane/hydrogen peroxide medium and aluminum substrate under charged and neutral species injection produced in negative corona discharges in air at atmospheric pressure is analyzed by different methods in this paper. The scanning electron microscopy investigations showed the uniform distribution of the pores formed in the alumina layer and their columnar structures. Both energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) measurements indicate that during the anodization process of the aluminum in the polydimethylsiloxane/hydrogen peroxide medium in corona discharge the incorporation of silicon in the structure of the alumina layer is possible.

92. Phytosynthesis of gold nanoparticles using caesalpinia pulcherrima (peacock flower) flower extract and evaluation of their antimicrobial activities

Authors: Nagaraj, B; Divya, TK; Barasa, M; Krishnamurthy, NB; Dinesh, R; Negrila, CC; Predoi, D

Published: MAR-APR 2013, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 15, 304, DOI:

Caesalpinia pulcherrima (Linn) popularly known as Peacock flower in India belongs to family Caesalpiniace. In this work, we describe environment friendly technique for green synthesis of gold nanoparticles from AuCl4 solution using the Caesalpinia pulcherrima (Peacock flower) flower extract as reducing agent. The gold nanoparticles were characterized using UV-visible spectroscopy and transmission electron microscopy (TEM). The UV- visible spectra indicate a strong Plasmon resonance that is located at similar to 450 nm. The TEM analysis shows that products have spherical morphology with size ranging between 1.0-50 nm. The study also indicates that gold nanoparticles show good antimicrobial activities when compared to the standard antibiotics.

93. Ga and As competition for thiolate formation at p-GaAs(111) surfaces

Authors: Preda, L; Negrila, C; Lazarescu, MF; Enache, M; Anastasescu, M; Toader, AM; Ionescu, S; Lazarescu, V

Published: AUG 1 2013, ELECTROCHIMICA ACTA, 104, 11, DOI: 10.1016/j.electacta.2013.04.077

Self-assembled layers of 4,4'-thio-bis-benzene-thiolate spontaneously adsorbed on p-doped GaAs(1 1 1)A and GaAs(1 1 1)B electrodes were examined by EIS, XPS, and AFM investigations. XPS data provide evidence that (i) both As and Ga atoms are involved in the thiolate formation no matter which one is prevailing on the semiconducting surface and (ii) only one of the two thiol groups participates in the chemisorption bond. EIS and AFM results point to a more stable thiolate layer formed on the As-terminated surface than that formed on the Ga-terminated surface due to stronger self-assembling effects developed between the adsorbed species. (C) 2013 Elsevier Ltd. All rights reserved.

94. ON THE PASSIVATION OF GaAs SURFACE BY SULFIDE COMPOUNDS

Authors: Ghita, RV; Negrila, CC; Cotirlan, C; Logofatu, C

Published: JUL-SEP 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1344, DOI:

A genuine GaAs surface is covered with a layer (similar to few nm) of native oxide pinning the surface Fermi level within the band gap of semiconductor. In this work is presented a study of GaAs surface passivation by sulfur compounds inorganic and organic (alkane thiols), a method that combines both chemical and electronic passivation. At the surface of GaAs it is developed an adherent layer of sulfur compound as a result of chemical interaction of sulfur ions with GaAs surface, a compound putted into evidence by scanning electron microscopy (SEM) images, photoluminescence analysis, second harmonic generation (SHG) measurement and Raman spectroscopy. Using X-ray photoelectron spectroscopy (XPS) it is putted into evidence the presence of covalent bonds Ga-S and AsS as a result of chemical interaction with sulf ions. Electrical characteristic of AuGeNi/thiol/GaAs structure is presented in I (V) recorded in the region of small currents.

95. Surface free energy of smooth and dehydroxylated fused quartz from contact angle measurements using some particular organics as probe liquids

Authors: Zgura, I; Moldovan, R; Negrila, CC; Frunza, S; Cotorobai, VF; Frunza, L

Published: JUL-AUG 2013, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 15, 634, DOI:

The dispersion and the polar independent contributions to the surface free energy in the case of fused quartz plates were evaluated by contact angle measurements against a series of liquids like water, glycerol, ethylene glycol, dimethyl sulfoxide and a nematic mixture NP5 of azoxybenzene type compounds. The smooth fused quartz plates were thermally pretreated at 240 degrees C and 1000 degrees C to decrease the number of surface hydroxyl groups; their surface was characterized by X-ray photoelectron spectroscopy. The contact angle data were further processed applying either the approach of Owens-Wendt with geometric mean or the Wu's approach of harmonic mean of nonpolar and polar interactions. The liquids were chosen thus to fulfill Della Volpe and Siboni's criterion namely that these have the condition number of system matrix low enough. The values obtained for the components of surface free energy were discussed in comparison with the results obtained in literature for crystalline quartz or for other silica forms as bulk or films. The study has shown a decrease of the polar component of the surface tension by increase of the pretreatment temperature.

96. Thermal analysis of corrosion products formed on carbon steel in ammonium chloride solution

Authors: Tutunaru, B; Samide, A; Negrila, C

Published: FEB 2013, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 111, 1154, DOI: 10.1007/s10973-011-2187-0

The influence of different ions NO3 (-) and SO4 (2-) on the carbon steel corrosion in ammonium chloride was investigated using mass loss measurements and potentiodynamic polarization. Corrosion products were analyzed using X-ray photoelectron spectroscopy (XPS) and simultaneous thermal and differential scanning calorimetry (TG/DSC). XPS analysis shows that the main product of corrosion is a non-stoichiometric Fe3+ oxyhydroxide, consisting of a mixture of FeO(OH) and FeO(OH) containing inclusions of these anions, species such as Fe3+O(OH,Cl-); Fe3+O(OH,SO4 (2-)); and Fe3+O(OH,NO3 (-)). TG/DSC confirms the decomposition of the rusty products formed by chemical corrosion, compounds like Fe3+ oxyhydroxides, with beta-FeOOH as the major phase, crystal structure of which may contain Cl-, NO3 (-), and SO4 (2-)-e.g., akaganeite [Fe3+O(OH,A)].

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

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

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

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

98. ATOMIC STRUCTURE AND MAGNETISM OF PLD DEPOSITED Tio(2):Fe

Authors: Costescu, RM; Lungu, GA; Socol, G; Gheorghe, NG; Macovei, D; Negrila, CC; Logofatu, C; Husanu, MA; Popescu, DG; Tache, CA; Teodorescu, CM

Published: JAN-MAR 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, DOI:

TiO2:Fe thin films prepared by pulsed laser deposition exhibit in some case light dependent saturation magnetization, as determined from Kerr magnetometry measurements performed in dark or by illuminating the sample. This phenomenon is studied in correlation with local atomic structure investigated by extended X-ray absorption fine structure, composition and chemical state analyzed by X-ray photoelectron spectroscopy and by X-ray absorption near-edge structure. It is found that light-controllable magnetism is a property of a mixture of Fe and oxidized Fe clusters embedded in the anatase TiO2 matrix.

99. Surface Analysis of Inhibitor Film Formed by 4-Amino-N-(1,3-thiazol-2-yl) Benzene Sulfonamide on Carbon Steel Surface in Acidic Media

Authors: Samide, A; Tutunaru, B; Negrila, C; Prunaru, I

Published: 2012, SPECTROSCOPY LETTERS, 45, 64, DOI: 10.1080/00387010.2011.598599

Inhibitive properties of the antibacterial sulfa drug sulfathiazole-IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide-on the corrosion of carbon steel in 1.0M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe3+ oxide/oxyhydroxide consisting of a mixture of Fe2O3, alpha, and gamma-FeO(OH) and/or Fe(OH)(3), where alpha, gamma-FeO(OH) is the main phase.

100. Study of the corrosion products formed on carbon steel surface in hydrochloric acid solution

Authors: Samide, A; Tutunaru, B; Dobritescu, A; Negrila, C

Published: OCT 2012, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 110, 152, DOI: 10.1007/s10973-011-2186-1

Effect of an antibacterial drug, sulfacetamide, IUPAC name N-[(4-aminophenyl) sulfonyl] acetamide (APSA), on the corrosion products formed on carbon steel surface in 1.0 mol L-1 HCl solution has been investigated using mass loss, X-ray photoelectron spectroscopy (XPS), and simultaneous thermal and differential scanning calorimetry/differential thermal analysis (TG/DSC/DTA). Mass loss measurements reveal that the corrosion rate of carbon steel is retarded by APSA and that the inhibition efficiency of this inhibitor increases with increasing the concentration. XPS analysis shows that, at this stage, the main product of corrosion is a non-stoichiometric Fe3+ oxyhydroxide, consisting of a mixture of FeO(OH) in anhydrous or hydrated forms, containing Cl- inclusions and adsorbed APSA molecules. The mechanism of inhibition was discussed in light of the chemical structure of the investigated inhibitor. The corrosion products were analyzed using TG/DSC/DTA technique.

101. PHYTOSYNTHESIS OF GOLD NANOPARTICLES USING CAESALPINIA PULCHERRIMA (PEACOCK FLOWER) FLOWER EXTRACT AND EVALUATION OF THEIR ANTIMICROBIAL ACTIVITIES

Authors: Nagaraj, B; Divya, TK; Barasa, M; Krishnamurthy, NB; Dinesh, R; Negrila, CC; Predoi, D

Published: JUL-SEP 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 905, DOI:

Caesalpinia pulcherrima (Linn) popularly known as Peacock flower in India belongs to family Caesalpiniace. In this work, we describe environment friendly technique for green synthesis of gold nanoparticles from AuCl4 solution using the Caesalpinia pulcherrima (Peacock flower) flower extract as reducing agent. The gold nanoparticles were characterized using UV-visible spectroscopy and transmission electron microscopy (TEM). The UV-visible spectra indicate a strong Plasmon resonance that is located at similar to 450 nm. The TEM analysis shows that products have spherical morphology with size ranging between 10-50 nm. The study also indicates that gold nanoparticles show good antimicrobial activities when compared to the standard antibiotics.

102. Electronic effects at self-assembled 4,4 '-thio-bis-benzenethiolate protected Au nanoparticles on p-GaAs (100) electrodes

Authors: Enache, M; Preda, L; Negrila, C; Lazarescu, MF; Mercioniu, I; Santos, E; Anastasescu, M; Dobrescu, G; Lazarescu, V

Published: AUG 30 2012, ELECTROCHIMICA ACTA, 77, 16, DOI: 10.1016/j.electacta.2012.04.161

The effects of the self-assembled 4,4'-thio-bis-benzenethiolate protected gold nanoclusters onto a p-GaAs (1 0 0) electrode were examined by AFM, XPS, SHG and EIS investigations. The AFM and XPS results revealed a well-ordered overlayer exhibiting a bi-modal highly correlated fractal behavior which, however, cannot fully protect the semiconducting surface against the oxidation in air. The EIS data pointed out the influence exerted by the gold-monolayer protected clusters (Au-MPCs) over the charging/discharging processes observed at p-GaAs (1 0 0) electrode. Although the applied potential is varied linearly, the potential drop within the semiconductor space charge region as well as that across the Au-MPCs layer undergoes stepped changes supposed to result in the discrete charging of the Au-MPCs. These effects point to an electronic equilibrium between the Au-MPCs and the semiconducting substrate. Fermi level pinning and enhancement of the SHG response in the potential range where the surface/interface states in the semiconductor band gap become electrically active bring further proof in this respect. (c) 2012 Elsevier Ltd. All rights reserved.

103. Study of thiols deposition on GaAs

Authors: Ghita, RV; Cotirlan, C; Ungureanu, F; Florica, C; Negrila, CC

Published: JAN-FEB 2012, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 6, 244, DOI:

A genuine GaAs surface is covered with a relatively thick layer (similar to nm) of native oxide pinning the Surface Fermi level within the band gap of semiconductor. The method presented in this work is related to sulfur passivation by treating n-GaAs in different solutions of alkane thiols. At the surface of GaAs it is developed an adherent layer of sulfur compound as a result of chemical interaction of sulfur ions with GaAs(100) face, that are putted in evidence by scanning electron microscopy (SEM) images and second harmonic generation (SHG) analysis. Using X-ray photoelectron spectroscopy (XPS) is presented a detailed analysis of XPS data at the surface of thiols on GaAs together with the presence of the covalent bond As-S. The electric characteristics of the AuGeNi/Thiol/GaAs structure are presented in I (V) curves recorded in the region of small currents.

104. Structural and optical properties of c-axis oriented aluminum nitride thin films prepared at low temperature by reactive radio-frequency magnetron sputtering

Authors: Galca, AC; Stan, GE; Trinca, LM; Negrila, CC; Nistor, LC

Published: DEC 1 2012, THIN SOLID FILMS, 524, 333, DOI: 10.1016/j.tsf.2012.10.015

Spectroscopic ellipsometry, X-ray diffraction and transmission electron microscopy experiments are employed to characterize aluminum nitride (AlN) thin films obtained by radio-frequency magnetron sputtering at low temperature (approximate to 50 degrees C). To understand the growth mechanism and to get in depth information of such films by using ex situ characterization techniques, the AlN thin film sample series were prepared for different sputtering times, while keeping constant all the other deposition conditions. The diffraction studies reveal a [002] oriented growth of the AlN thin films. The misorientation of this crystallographic axis to the normal to the surface reduces progressively with film growth. A nonmonotonic behavior of the AlN pseudo-refractive index versus deposition time indicates a complex depth profile of the AlN thin films optical properties. The difference in orientation dispersion of the [002] crystallite axis, the variation of defects concentration and each constituent atom density influence the refractive index evolution. Our interpretation validity was verified by producing and characterizing samples obtained at intermediate deposition time. The AlN thin films show also very good pull-out adherence values. (C) 2012 Elsevier B. V. All rights reserved.

105. Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion

Authors: Papa, F; Negrila, C; Dobrescu, G; Miyazaki, A; Balint, I

Published: SEP 2011, JOURNAL OF NATURAL GAS CHEMISTRY, 20, 542, DOI: 10.1016/S1003-9953(10)60221-6

Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.

106. EFFECT OF SULFACETAMIDE ON THE COMPOSITION OF CORROSION PRODUCTS FORMED ONTO CARBON STEEL SURFACE IN HYDROCHLORIC ACID

Authors: Samide, A; Tutunaru, B; Negrila, C; Trandafir, I; Maxut, A

Published: APR-JUN 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 673, DOI:

Effect of an antibacterial drug, sulfacetamide, IUPAC name N-[(4-aminophenyl) sulfonyl] acetamide (APSA) on the corrosion of carbon steel in 1.0 M HCl solution has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and XPS analysis. The electrochemical measurements indicated that the presence of APSA in 1.0 M HCl solution decreases the corrosion current (i(corr)) and increases the polarization rezistance (R-p). XPS surface analysis showed at this stage, in the absence of APSA, that the main product of corrosion is a non-stoichiometric Fe3+ oxide/oxide-hydroxide, consisting of a mixture of Fe2O3 and FeO(OH), where FeO(OH) is the main phase. Moreover, in presence of inhibitor the surface layer consists of FeO(OH) rather than pure oxide, adsorbed molecules of sulfacetamide and inorganic compounds such as: sulfides, carbonates, sulphates, nitrates, which were obtained by electrochemical degradation of APSA. UV-Vis spectrophotometry and HPLC technique were performed to determine the medium composition before and after corrosion. The results showed a decrease of the inhibitor concentration in 1.0 M HCl solution after carbon steel corrosion, indicating an adsorption process between organic compound molecules from aqueous phase and the electrode surface and/or the electrochemical degradation of APSA.

107. Study of SiO2/Si Interface by Surface Techniques

Authors: Logofatu, C; Negrila, CC; Ghita, RV; Ungureanu, F; Cotirlan, C; Manea, CGAS; Lazarescu, MF

Published: 2011, CRYSTALLINE SILICON - PROPERTIES AND USES, 42, DOI:

108. Corrosion Inhibition of Carbon Steel in Hydrochloric Acid Solution Using a Sulfa Drug

Authors: Samide, A; Tutunaru, B; Negrila, C

Published: SEP 2011, CHEMICAL AND BIOCHEMICAL ENGINEERING QUARTERLY, 25, 308, DOI:

The corrosion inhibition of carbon steel in 1.0 mol L(-1) HCl in the presence of an antibacterial sulfa drug Sulfathiazole, IUPAC name 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide (TBSA) was investigated using mass loss and electrochemical measurements such as: potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). For the study of the surface morphology scanning electron spectroscopy (SEM) was used. The results showed that TBSA acts as a corrosion inhibitor in 1.0 mol L(-1) HCl solution by suppressing simultaneously the cathodic and anodic processes via adsorption on the carbon steel surface and that the inhibition efficiency increases with increasing concentration. XPS analysis revealed that the corrosion product consists of an oxyhydroxide/oxide mixture and that the iron oxyhydroxide proportion is higher than the iron oxide proportion.

109. Morphology and chemical state of PVP-protected Pt, Pt-Cu, and Pt-Ag nanoparticles prepared by alkaline polyol method

Authors: Papa, F; Negrila, C; Miyazaki, A; Balint, I

Published: OCT 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 5064, DOI: 10.1007/s11051-011-0486-9

Well-dispersed, uniform monometallic Pt and bimetallic Pt-Cu, and Pt-Ag nanoparticles protected with PVP have been synthesized by a modified-protocol alkaline polyol method. The nanoparticles were characterized by various methods (TEM, XPS, and XRD) to elucidate the relationship between morphology and preparation variables. The average of monodispersed nanoparticles ranged between 4.1 and 4.9 nm. Core-shell structure was obtained in the case of bimetallic nanoparticles. The core of bimetallic nanoparticles was found to be rich in platinum, whereas the shell contained mostly copper or silver. The final structure of bimetallic nanoparticles was found to be determined by the morphology particles resulted in the first reduction step. Explanations are advanced on the light of experimental results.

110. Structural and chemical properties of cerium-magnetoplumbite in cerium based IT-SOFC compounds

Authors: Vlaicu, AM; Mercioniu, I; Vasile, BS; Negrila, CC; Logofatu, C; Cretu, NC; Nita, P; Popescu-Pogrion, N

Published: JAN 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 145, DOI:

Yttria doped ceria reinforced with yttria doped alumina compound for IT-SOFC applications has been prepared by sol-gel method and sintered at 1300 degrees C, 1400 degrees C, 1500 degrees C. XRD, and SEM show the presence of a needle-like cerium-magnetoplumbite (CeAl11O17) phase in the compound; the oxygen deficient phase grows from the alumina phase by using ceria from the surrounding matrix and releasing oxygen ions As the sintering temperature is increased, the alumina phase is gradually transformed into CeAl11O17. Compared to the yttria doped ceria without reinforcement, the obtained compounds with ceria-magnetoplumbite show only a slight decrease of the Young elasticity modulus. However, the samples become brittle after backing in oxygen atmosphere (1000 degrees C, and 1500 degrees C).

111. EVALUATION OF PROTECTIVE PROPERTIES OF POLY (VINYL) ALCOHOL THIN FILM FORMED ON STAINLESS STEEL FOR ORTHOPEDIC IMPLANT APPLICATIONS

Authors: Samide, A; Negrila, C; Ciuciu, A

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 1008, DOI:

The surface characterization of 304L stainless steel for orthopedic implant applications, unmodified and modified with poly (vinyl) alcohol (PVA) in physiological serum (PS) is discussed according to electrochemical measurements, Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM / EDS) and X-ray Photoelectron Spectroscopy (XPS) techniques. The results obtained through polarization curves indicate that PVA reduces anodic dissolution and also decrease of the corrosion current (i(corr)); decrease of the corrosion current (i(corr)) was associated with a shift of corrosion potential (E-corr) to a less negative values; the polarization resistance(R-p) increases for the surfaces which were treated in physiological serum in the presence of PVA. SEM / EDS and XPS analysis showed that the surface layer which was formed on 304L stainless steel consists of PVA containing of small amount of other elements, such as: Na and Cl.

112. Nanostructured gold layers. I. Deposition by Vacuum evaporation at small angles of incidence

Authors: Beica, T; Frunza, S; Zgura, I; Frunza, L; Cotarlan, C; Negrila, C; Vlaicu, AM; Zaharia, CN

Published: FEB 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 353, DOI:

Gold layers were deposited at oblique incidence onto glass plates. A B30.2 Hochvakuum Bedampfungsanlage equipment was used in this aim. The deposition conditions were chosen in order to obtain nanostructured layers. Correlations were found among these conditions and the corresponding nomograms were then obtained. Examples of such depositions were given and the layers structure was characterized and additionally supported by observing the molecular alignment given in the liquid crystal cells obtained with these gold layers.

113. Nanostructured thin layers of vanadium oxides doped with cobalt, prepared by pulsed laser ablation: chemistry, local atomic structure, morphology and magnetism

Authors: Teodorescu, CM; Socol, G; Negrila, C; Luca, D; Macovei, D

Published: 2010, JOURNAL OF EXPERIMENTAL NANOSCIENCE, 5, 526, DOI: 10.1080/17458081003671675

Cobalt-doped vanadium oxide thin layers prepared by pulsed laser ablation are investigated from the following points of view: (1) the chemical states by X-ray photoelectron spectroscopy (XPS), (2) the local atomic order by X-ray absorption fine structure at both vanadium and cobalt K-edges, (3) the morphology of the films by atomic force microscopy (AFM) and (4) the magnetic properties by magneto-optical Kerr effect (MOKE). The chemical composition of the host matrix was found to be close to VO2 at the sample surface, with V2O3 in the bulk. Co ions are found near the surface in high ionisation states Co4+ (for the samples synthesised in a high vacuum condition, denoted by VO1), or with Co(4-)+ (for the samples synthesised in an oxygen atmosphere, denoted by VO2), whereas in the bulk, Co1.5+ is obtained for VO1 and Co2+ is obtained for VO2. The AFM revealed nanoparticles with sizes 10-25 nm for VO1 samples, whereas a few bigger nanoparticles are observed for VO2 samples. The VO1 samples presented high coercitive fields with a relatively low saturation magnetisation at room temperature, superposed with a superparamagnetic component attributed to the observed nanoparticles, whereas the VO2 samples presented double-loop hysteresis curves, indicating the co-existence of two kinds of magnetic moieties with antiparallel coupling at zero applied field. The proposed two magnetic phases are Co-doped V2O3 and VO2.

114. XPS study of chemically sulphur-passivated n-GaAs

Authors: Ghita, RV; Negrila, CC; Ungureanu, F; Logofatu, C

Published: NOV 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1739, DOI:

A genuine GaAs surface was covered with a relatively thick layer (similar to nm) of native oxide pinning the surface Fermi level within the band gap of semiconductor. The method presented in this work is related to the sulphur passivation by treating n-GaAs in sulphide solutions (e.g. pure ammonium sulphide and sulphur monochloride) that combines both chemical and electronic passivation by reducing the surface state density. The presence of the covalent bonds As-S and Ga-S was putted into evidence by XPS analysis. It is presented the independence of XPS measurements on n-GaAs substrate orientation for (100) and (110) planes. At the surface of n-GaAs it is developed an adherent layer of sulphur compound as a result of chemical interaction of sulphur ions with n-GaAs surface.

115. ASPECTS OF TEMPERATURE DEPENDENCE ON Au-Ti/GaAs(SI) SCHOTTKY BARRIER

Authors: Negrila, CC; Ungureanu, F; Ghita, RV

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 458, DOI:

Fabrication of Au-Ti Schottky structure on GaAs semi-insulating wafer was related to an ultra-high vacuum deposition condition and low vacuum annealing in low vacuum and temperature range T=320-360 degrees C. There are presented representative I-V characteristics in dark and in different light (power levels). The spectral response has a maximum in Delta lambda = (850-950) nm corresponding to a band-to-band transition. The complex dependence of optical generated non-equilibrium carriers is related to the equivalent state density at the conduction band edge (in T(3/2) factor) and in exponential distribution factor exp (-(E-F)/kT).

116. Total oxidation of toluene on ferrite-type catalysts

Authors: Florea, M; Alifanti, M; Parvulescu, VI; Mihaila-Tarabasanu, D; Diamandescu, L; Feder, M; Negrila, C; Frunza, L

Published: MAR 30 2009, CATALYSIS TODAY, 141, 366, DOI: 10.1016/j.cattod.2008.05.005

Ferrite catalysts were prepared following two routes, i.e. the hydrothermal one and the calcination of an oxide mixture. In the first route sodium hydroxide, ferrous sulfate and the sulfate of the substituting ion (Mn, Ni) were used. The ferrites obtained using this route was NixFe3-xO4 (x = 0.5) and MnxFe3-xO4 (x similar to 0.65). Following the second route were prepared three samples: NiFe2O4, Ni0.5Zn0.5Fe2O4 and MnFe2O4. Two of them contain the corresponding ferrites while the latter is a presintered oxide mixture (Fe2O3-Mn2O3). All the samples were fully characterized using chemical analysis, X-ray fluorescence spectroscopy and EDX, nitrogen adsorption-desorption isotherms at -196 degrees C, X-ray diffraction (XRD), FTIR, scanning electron microscopy and XPS. The catalytic activity evaluation was made using a mixture of 1700 ppm vol. of toluene and air flowing at 100 ml min(-1) raising the temperature up to 600 degrees C in steps of 25 degrees C. Among these systems the sample representing the presintered Fe2O3-Mn2O3 mixture showed the highest activity. (C) 2008 Elsevier B.V. All rights reserved.

117. Thin films of Cu(II)-o,o '-dihydroxy azobenzene nanoparticle-embedded polyacrylic acid (PAA) for nonlinear optical applications developed by matrix assisted pulsed laser evaporation (MAPLE)

Authors: Constantinescu, C; Emandi, A; Vasiliu, C; Negrila, C; Logofatu, C; Cotarlan, C; Lazarescu, M

Published: MAR 1 2009, APPLIED SURFACE SCIENCE, 255, 5485, DOI: 10.1016/j.apsusc.2008.10.012

Thin films based on two different metal-organic systems are developed by MAPLE and their nonlinear optical applications are explored. A complex of o,o'-dihydroxy azobenzene with Cu(2+) cation is found to organize as a non-central symmetric crystallite. A simple protocol is developed for the in situ fabrication of highly monodisperse copper-complex nanoparticles in a polymer film matrix of polyacrylic acid. The thin films were deposited on quartz substrates by MAPLE ( matrix assisted pulsed laser evaporation) using a Nd:YAG laser working at 355 nm. Atomic force microscopy (AFM), Fourier transform infrared ( FTIR), X-ray photoelectron spectroscopy (XPS), and optical second harmonic generation (SHG) were performed on the samples. The optical limiting capability of the nanoparticle-embedded polymer film is investigated. (C) 2008 Elsevier B. V. All rights reserved.

118. XPS analysis of n-GaP(111) native and etched surfaces

Authors: Cotirlan, C; Logofatu, C; Negrila, CC; Ghita, RV; Manea, AS; Lazarescu, MF

Published: APR 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 390, DOI:

The obtaining of a good ohmic contacts on the semiconductor material surfaces is strongly depending on the ability of the cleaning procedures to remove the native oxides and also, in the case of the compounds, to keep the surface stoichiometry. In this work, the XPS technique has been used in order to compare the efficiency of both, chemical etching and the Ar+ ion sputtering methods as to be suitable cleaning procedures in the case of n-GaP semiconductor compound surfaces preparation for the optoelectronic devices obtaining. The results have revealed some differences in the final surface composition/stoichiometry. The atomic ratio P/Ga within the outer layer of the single crystalline sample (similar to 100 angstrom) has been evaluated. The presence of residual of surface oxides was recorded after performing the chemical cleaning.

119. Optical and structural investigations on rare earth-doped thin films of phosphate glasses prepared by pulsed laser deposition

Authors: Vasiliu, C; Epurescu, G; Niciu, H; Dumitrescu, O; Negrila, C; Elisa, M; Filipescu, M; Dinescu, M; Grigorescu, CEA

Published: JAN 2009, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 20, 289, DOI: 10.1007/s10854-008-9583-7

Thin films of phosphate glasses were prepared by pulsed laser deposition in oxygen atmosphere on ITO-coated glass and silicon substrates respectively, using a Nd:YAG laser (266 nm). The targets were Li(2)O-Al(2)O(3)-P(2)O(5) bulk glasses doped with Pr and Nd. Infrared transmission-, energy dispersive X-ray- and X-ray photoemission spectroscopy investigations carried out on targets as well as on the deposited films proved a satisfactory compositions transfer on both substrates. Scanning electron microscopy and atomic force microscopy show continuous films with glassy spheres. Processes where substrates were positioned perpendicularly to targets produced discontinuous drops free films.

120. Pulsed laser co-deposition of titania with Fe: chemistry, local atomic structure, and light-dependent magnetic properties

Authors: Negrila, C; Logofatu, C; Socol, G; Macovei, D; Teodorescu, CM

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:

TiO2:Fe thin films prepared by pulsed laser deposition exhibit in some case light dependent saturation magnetization, as determined from Kerr magnetometry measurements performed in dark or by illuminating the sample. This phenomenon is Studied in correlation with local atomic Structure investigated by extended X-ray absorption fine structure, composition and chemical state analyzed by X-ray photoelectron spectroscopy and by Xray absorption near-edge structure. It is found that light-controllable magnetism is a property of a mixture of Fe and oxidized Fe clusters embedded in the anatase TiO2 matrix.

121. Fabrication and characterization of nano-structured ferromagnetic Ti1-xFexO2 thin films

Authors: Apetrei, R; Negrila, C; Macovei, D; Dascaleanu, V; Teodorescu, CM; Mardare, D; Luca, D

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:

Nanostructured intrinsic and doped titania materials have long been subject to both basic and applied research, in connection with environment and energy related applications. Apart from beneficial effects. such as widening the wavelength range for surface photocatalytic activation, doping TiO2 materials with 3d ferromagnetic cations is a main route to develop ail important class of diluted semiconductors, with potential applications in spintronics. In all the previous investigations the concentration of the ferromagnetic dopant was limited to a few percents. Here, we initiate ail extended investigation of Ti1-xFexO2 within a, wider iron composition range (x = 0 - 0.55) and discuss the magnetic and optical properties of these materials in thin films in relation with their elemental composition, nano-structure and local atomic ordering.

122. Preparation and characterization of nitrogen-doped TiO2 nanoparticles by the laser pyrolysis of N2O-containing gas mixtures

Authors: Alexandrescu, R; Scarisoreanu, M; Morjan, I; Birjega, R; Fleaca, C; Luculescu, C; Soare, I; Cretu, O; Negrila, CC; Lazarescu, N; Ciupina, V

Published: MAR 1 2009, APPLIED SURFACE SCIENCE, 255, 5377, DOI: 10.1016/j.apsusc.2008.08.046

Nitrogen-doped TiO2 nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl4 (vapors) and N2O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18 nm in case of the almost pure anatase sample to about 13 nm in case of the anatase-rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process. (C) 2008 Elsevier B. V. All rights reserved.

123. Characteristics of arc plasma deposited TiAlZrCN coatings

Authors: Balaceanu, M; Braic, V; Kiss, A; Zoita, CN; Vladescu, A; Braic, M; Tudor, I; Popescu, A; Ripeanu, R; Logofatu, C; Negrila, CC

Published: MAY 15 2008, SURFACE & COATINGS TECHNOLOGY, 202, 3987, DOI: 10.1016/j.surfcoat.2008.02.005

TiAlZrCN superhard coatings, in which Ti and Al were additions to ZrCN base compound, were prepared by the cathodic arc method. The films were deposited on Si, plain carbon steel and high-speed steel substrates in a mixture of N-2 and CH4 gases. Elemental and phase composition, chemical bondings, texture, surface roughness, hardness, adhesion, tribological characteristics and erosive-corrosive resistance were investigates as a function of gas composition and total gas flow rate, using XPS, GDOES and XRD techniques, surface profilometry, microhardness and scratch adhesion measurements, tribological and erosive tests. It was shown that the properties and performance of the coatings were strongly dependent on the CH4/(CH4+N-2) flow rate and also on the total gas flow. The tribological and anti-erosive characteristics of the TiAlZrCN coatings were found to be superior to those of reference films (ZrN, ZrC, ZrCN, and TiAlCN). Maximum hardness values (42-45 GPa) were obtained for the films prepared at CH4/(CH4+N2) ratios ranging from 0.2 to 0.4. (c) 2008 Elsevier B.V. All rights reserved.

124. Capacitance-voltage characteristics of heterostructures with high leakage currents

Authors: Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Pintilie, I; Negrila, C; Botila, T

Published: MAR 1 2008, JOURNAL OF APPLIED PHYSICS, 103, DOI: 10.1063/1.2844210

Leakage currents determine bumps in the capacitance-voltage characteristics of metal-oxide-semiconductor-type heterostructures with capacitance values larger than the insulator capacitance. A nearly parallel shift with frequency is also observed. These aspects are connected with the presence of a high density of interface states. We illustrate these effects for the case of nano-PbS/SiO2/Si heterostructures. The phenomena were simulated and we propose a method to quickly estimate the interface state density level of a heterostructure when leakage channels are present. (C) 2008 American Institute of Physics.

125. Nanostructured thin layers of vanadium oxides doped with cobalt, prepared by pulsed laser ablation: structure, chemistry, morphology, and magnetism

Authors: Teodorescu, CM; Socol, G; Negrila, C; Luca, D; Macovei, D

Published: 2008, NSTI NANOTECH 2008, VOL 1, TECHNICAL PROCEEDINGS: MATERIALS, FABRICATION, PARTICLES, AND CHARACTERIZATION, 438, DOI:

Cobalt-doped vanadium oxide thin layers prepared by pulsed laser ablation are investigated by (i) X-ray photoelectron spectroscopy, (ii) the local atomic order by X-ray absorption near-edge structure (XANES), (iii) the morphology of the films was investigated by atomic force microscopy (AFM), and (iv) magnetic properties were quantified by magneto-optical Kerr effect (MOKE). In most cases, the chemical composition of the host matrix was found to be the vanadium (5+) oxide V2O5 at the sample surface and lower ionization states (+2 and +3) in the bulk. Co ions are found either in high ionization state Co5+ (for samples synthesized in high vacuum condition, denoted by VO1), or with Co in lower ionization states Co4+ (for samples synthesized in a mixture of argon and oxygen atmosphere, denoted by VO2). Consistent information was obtained from chemical shifts from individual core level scans in XPS, compared with existent data in litterature, and the amplitude of the pre-edge peak in XANES, which is a sign of quadrupole 1s -> 3d dipole-forbidden transition and whose amplitude is proportional to the number of 3d vacancies per atom. AFM revealed big particles with sizes > 100 mu m for VO1 samples, whereas smaller nanoparticles with sizes ranging between 20 and 30 mu m were observed for VO2 samples. VO1 samples presented very high coercitive fields with a relatively low saturation magnetisation at room temperature, whereas VO2 samples presented double-loop hysteresis curves, indicating the coexistence of exchange bias between two kinds of magnetic moieties with strong anisotropy.

126. ARXPS analysis of silicon oxide films

Authors: Negrila, CC; Cotirlan, C; Ungureanu, F; Logofatu, C; Lazarescu, RVGMF

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1383, DOI:

Angle-resolved X-ray Photoelectron Spectroscopy (ARXPS) has been performed on (100) Si surfaces in different conditions as regards the oxides nature - native oxides, thermally formed oxides, and also after a cleaning procedure by Ar+ ion sputtering (e.g. E= 2 keV). The most sensitive angle to surface oxidation states (Si1+, Si2+, Si3+, Si4+) was the take-off-angle (TOA): 25 degrees. Native oxides and thermally oxide phases on Si surfaces consists in a mixture of Si2O, SiO, Si2O3 and SiO2. The XPS measurements have putted into evidence a higher concentration of suboxides in high oxidation state (Si3+) on naturally oxidized Si substrates. The thermally oxidized Silicon surfaces contain suboxides in a low oxidation state (Si1+). The Ar+ ion sputtering removed rapidly the superficial silicon oxides. The analysis and computation of SiO2 film thickness on crystalline Silicon was done in the frame of modified Bethe equation for Electron inelastic mean free path (IMFP) and taking into account the intensity of SiO2 peak and Si peak together with the TOA in the XPS measurement. Native oxide thickness for SiO2 was d(oxy) similar to 24 angstrom and for thermally oxidized sample was d(oxy) similar to 27 angstrom. Due to the slightly difference in the nature oxidation states it is suggested that the silicon dioxide appeared from two different kinetics in the oxidation processes.

127. Electrical characterization of thiols self-assembled layers on GaP (111) structures

Authors: Ghita, RV; Lazarescu, V; Logofatu, C; Negrila, CC; Lazarescu, MF

Published: OCT 2008, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 11, 397, DOI: 10.1016/j.mssp.2008.11.012

The experimental studies on III-V semiconductor compounds surface passivation phenomena are mainly dedicated to solve some technological problems as those regarding the ways to keep the chemical stability of native oxides on surfaces. Self-assembled monolayers (SAMs) provide a simple way to produce relatively ordered structures at a molecular scale, which seems to be capable to protect the clean surface against the evolution of oxidation process. In this respect, thin films of SAMs of aliphatic thiol (dodencanthiol-CH3(CH2)(11)SH) and aromatic thiol (4, 4' tiobisbenzenthiol-S (C6H4SH)(2) have been deposited on the surface of Gap (111) samples. The electrical properties measurements of some structures based on GaP compound was performed. There were recorded current-voltage (I-V) characteristics for complex structures AuGeNi/R-SH/GaP and AuGeNi/Ar-SH/GaP in darkness and also exposed to a Xe lamp. In dark and in "reverse bias" way, the I-V characteristics present the feature of a Zenner diode for GaP/Ar-SH and a gradual increase of current for GaP/R-SH. In dark and "in forward bias" way, the current increases as for a normal diode for both GaP/Ar-SH and GaP/R-SH structures. The complex structures (e.g.: In/AuGeNi/R-SH/GaP/R-SH/AuGeNi/In) are less sensitive to light. The SEM analysis performed on a GaP/R-SH surface shows a continuous packed up layer while GaP/Ar-SH looks like an inhomogeneous deposition of layers with different thickness regions. The diodes' ideality factors determined from I-V characteristics are unusually high (n >> 2) as a possible result of inhomogeneous Schottky contacts or due to ageing effects, in the field of degradation. (C) 2009 Elsevier Ltd. All rights reserved.

128. Angle-resolved XPS structural investigation of GaAs surfaces

Authors: Negrila, CC; Logofatu, C; Ghita, RV; Cotirlan, C; Ungureanu, F; Manea, AS; Lazarescu, MF

Published: APR 2008, JOURNAL OF CRYSTAL GROWTH, 310, 1582, DOI: 10.1016/j.jcrysgro.2007.11.001

Angle-resolved X-ray photoelectron spectroscopy (ARXPS) analysis has been performed on GaAs (10 0) surfaces in different conditions as naturally oxidized, Ar+ ion sputtering (E = 1-5 keV) and chemical etching in H2SO4/H2O2/H2O(3: 1: 1). The most sensitive angle to the surface compositional changes was the take-off angle (TOA): 25 degrees. Native oxide phases on GaAs consist of a mixture of Ga2O3, As2O3 and As2O5. Ar+ ion sputtering procedure modifies the surface composition, in the altered layer where the concentration ratio C-Ga/C-As tends to 1.5-1.6. Wet chemical etching removes the oxide layer and the As-rich region from the surface. In the experiment combining chemical etching with Ar+ ion sputtering for cleaning purpose, the native oxides are removed from the surface and C-Ga/C-As tends to stoichiometry. The experiment on native oxide reconstruction after storage in high-vacuum conditions (P similar to 10(-8) Torr) provides evidence of the high reactivity of GaAs (10 0) surfaces. We have observed the presence of an As oxide (BE = 43 eV) within a concentration range of 2-3%. (C) 2007 Elsevier B.V. All rights reserved.

129. Influence of bilayer period on the characteristics of nanornetre-scale ZrN/TiAIN multilayers

Authors: Vladescu, A; Kiss, A; Popescu, A; Braic, M; Balaceanu, M; Braic, V; Tudor, I; Logofatu, C; Negrila, CC; Rapeanu, R

Published: FEB 2008, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 8, 721, DOI: 10.1166/jnn.2008.D218

in the last decade, considerable research effort was directed to the deposition of multilayer films with layer thicknesses in the nanometer range (superlattice coatings), in order to increase the performance of various cutting tools and machine parts. The goal of the present work was to investigate the main microstructural, mechanical and wear resistance characteristics of a superlattice coating, consisting of alternate multilayer ZrN/TiAIN films, with various bilayer periods (5 divided by 20 nm). The coatings were deposited by the cathodic arc method on Si, plain carbon steel and high speed steel substrates to be used as wear resistance surfaces. The multilayer structures were prepared by using shutters placed in front of each cathode (Zr and Ti + Al). The characteristics of multilayer structures (elemental and phase composition, texture, Vickers microhardness, thickness, adhesion, and wear resistance) were determined by using various techniques (AES, XPS, XRD, microhardness measurements, scratch, and tribological tests). A comparison with the properties of ZrN and TiAIN single-layer coatings was carried out.

130. Structural and optical properties of the SiO2-P2O5 films obtained by sol-gel method

Authors: Vasiliu, I; Gartner, M; Anastasescu, M; Todan, L; Predoana, L; Elisa, M; Negrila, C; Ungureanu, F; Logofatu, C; Moldovan, A; Birjega, R; Zaharescu, M

Published: JUN 4 2007, THIN SOLID FILMS, 515, 6605, DOI: 10.1016/j.tsf.2006.11.106

A comparative study of the sol-gel films prepared in the SiO2-P2O5 system starting with triethylphosphate, triethylphosphite and phosphoric acid as P precursors was performed. The work addresses basic aspects of physics, chemistry, and engineering of oxide films for applications in microelectronics, sensing, nano-photonics, and optoelectronics by establishing the influence of different precursors on the composition, structure and optical properties of the obtained films. The influence of the type of substrate (glass and indium tin oxide coated glass) and of the thermal treatment (200 and 500 degrees C on their structure and properties was studied. By spectroscopic ellipsometry, X-Ray photoemission spectroscopy and atomic force microscopy measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when P-alkoxides were used. The phosphoric acid that forms chemical bond with silica network during the sol-gel process leads to better incorporation of P in the silica network as compared to the P-alkoxides. (C) 2006 Elsevier B.V. All rights reserved.

131. Surface-analytical and EPR studies on sediment samples in Herastrau Lake, Romania

Authors: Seletchi, ED; Negrila, C; Duliu, OG; Turcas, CV

Published: SEP 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2953, DOI:

X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) have been used to investigate the elemental composition, chemical and electronic state of elements that exist within the Herastrau Lake (Bucharest, Romania) sediments. XPS spectra were obtained by irradiating the sediment samples with an Al source of X-rays (1486.6 eV). C, N, O, F, Na, Mg, Al, Si, S, Cl, K, Ca, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb have been determined by XPS and AES techniques. The analysis of Electron Paramagnetic Resonance (EPR) spectra revealed an additional free radical peak in the center of Mn2+ sextet, at a g = 2.0038, attributed to SO3- species as well a very intense and broad signal due to Fe3+ ions.

132. Spectral response of Au-Ti Schottky barrier on semi-insulating GaAs

Authors: Ghita, RV; Logofatu, C; Negrila, C; Cotirlan, C; Ghita, P; Manea, AS; Lazarescu, MF

Published: APR 2007, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 204, 1029, DOI: 10.1002/pssa.200674107

For the fabrication of the rectifying contact, respectively the Schottky diode structure on semi-insulating GaAs (100) oriented, Cr-doped, with a resistivity of rho similar to 10(6) - 10(7) Omega cm we have used Au-Ti contact. The Ti contact was deposited on a plasma etched GaAs surface in high vacuum (10(-8) torr), Au was deposited in medium vacuum (10(-6) torr) and the Au-Ti/GaAs interface was formed by a rapid thermal annealing procedure at T = 320 - 360 degrees C in low vacuum (10(-1) torr). The representative I-V characteristics in dark and under illumination at different power levels are presented. It is worth to mention that we estimate a barrier height of Phi(B) similar to 0.84 V (in the frame of thermionic emission model). The spectral response at two operating points and at different temperatures is presented. The signal has a maximum in the Delta lambda range (850-950) nm, which corresponds to the generation of photo-carriers due to a band-to-band direct transition. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

133. Electrical characteristics of nano-PbS/SiO2/Si heterostructures obtained by chemical bath method

Authors: Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Botila, T; Negrila, C

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3802, DOI:

The PbS/SiO2/Si structures show a clockwise hysteresis of capacitance-voltage (C-V) characteristics. The loop width increases with temperature and sweep time. The conductance-voltage (G-V) characteristics also present a hysteresis effect with two bumps. Both characteristics show a strong shift with frequency. We show that these effects are determined by the positive mobile ions injected in the oxide region during the chemical bath deposition of PbS and by the high concentration Of Si/SiO2 interface states. The corresponding C-V and G-V characteristics are simulated and the main peculiarities of the experimental results are well reproduced by the modeled curves.

134. Properties of TiO2 thin films prepared by different techniques

Authors: Ungureanu, F; Medianu, R; Ghita, RV; Negrila, CC; Ghita, P; Manea, AS; Lazarescu, MF

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1461, DOI:

TiO2 thin films prepared by sol-gel method and by RF magnetron sputtering deposited on p-Si(111), n-GaAs(100), and glass have been investigated by XRD, XPS and AFM techniques. The characteristics of the film: colour, adherence and composition are presented in the case of thermal treatments (500 degrees C and 800 degrees C) for sol-gel deposited films as well as for RF sputtering. The TiO2 plasma deposited film is uniform, homogeneous and stoichiometric.

135. Influence of the phosphorous precursors on the structure and properties of the SiO2-P(2)O(5)sol-gel films

Authors: Vasiliu, C; Grigorescu, C; Pavelescu, G; Predoana, L; Todan, L; Gartner, M; Anastasescu, M; Negrila, C; Logofatu, C; Moldovan, A; Zaharescu, M

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1410, DOI:

Thin films in the SiO2-P2O5 system are intensely studied due to their applications in microelectronics, sensing, nanophotonics, optoelectronics and as ionic conductors. Sol-gel is the most used method for preparation of such films. Previous studies established the very low reactivity of the phosphorous alkoxides and the high tendency of the phosphorous oxide to volatilise at thermal treatment. In order to identify the most appropriate precursor for obtaining layers with desired composition and properties a systematic study of the sol-gel film preparation using different phosphorous precursors was carried out. The films were deposited on ITO/SiO2 coated glass substrates at room temperature. To check the influence of the type of precursors on the layers thermal stability and properties a post deposition annealing was performed at temperatures of 150 and 200 degrees C. The film characterization was carried out using various techniques as Spectroscopic Ellipsometry (SE), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR).

136. SiOx-P2O5 films: promising components in photonic structure

Authors: Vasiliu, I; Gartner, M; Anastasescu, M; Todan, L; Predoana, L; Elisa, M; Grigorescu, C; Negrila, C; Logofatu, C; Enculescu, M; Moldovan, A; Pavelescu, G; Zaharescu, M

Published: MAR 2007, OPTICAL AND QUANTUM ELECTRONICS, 39, 521, DOI: 10.1007/s11082-007-9096-2

We intend to prepare periodic multilayered structures for photonic applications. With this goal we have performed a study of some characteristics of SiO (x) -P2O5 films deposited by the sol-gel method on glass and ITO (InSnO (x) )-coated glass. The as prepared films were annealed to different temperatures (150 and 200 degrees C). The chemical composition of the samples was determined by X-ray Photoelectron Spectroscopy (XPS). The XPS results revealed the presence of P in the as-deposited films. The structural an optical properties were examined by Fourier Transform Infrared Spectroscopy (FTIR), Spectroellipsometry (SE) and UV Transmission Spectroscopy. IR spectra of the deposited films attest the interaction of an amorphous SiO2 with the H3PO4 used as a P-precursor. Refractive indices for individual SiO (x) -P2O5 determined from SE measurements show a densification of the layer structure with the increasing temperature in the thermal treatment. The UV transmission spectra revealed a lower transmission for the sol-gel SiO (x) -P2O5 films as compared to ITO/glass substrate. AFM images proved the densification of the films with annealing in agreement with the ellipsometric results.

137. XPS, AES and ESR studies of Herastrau Lake sediments, Bucharest, Romania

Authors: Seletchi, ED; Negrila, C; Duliu, OG; Turcas, CV

Published: 2007, SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION, 899, +, DOI:

X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) have been used to investigate the elemental composition, chemical and electronic state of elements that exist within the Herastrau Lake (Bucharest, Romania) sediments. XPS spectra were obtained by irradiating the sediment samples with an Al source of X-rays (1486.6 eV). A very broad peak at 165-190 eV corresponds to sulfur oxides, sulfate and sulfite ions and sulfur hexafluoride. The measurements indicate metal oxides: (Al2O3, Fe2O3) at 528-531 eV, SiO2 at 533 eV, phosphates, nitrates at 531-533 eV, silicates at 532-533 eV, CaO, CaCO3 and CaS at 346-347 eV, CaSo(4) at 348 eV, Ca(NO3)(2) at 349 eV and slight traces of NH3. A very intense peak at 784 eV also appears due to CoSO4. The analysis of Electron Spin Resonance (ESR) spectra revealed an additional free radical peak in the center of Mn2+ sextet, at a g = 2.0038, attributed to SO3- species as well a very intense and broad signal due to Fe3+ ions.

138. Characteristics of hydroxyapatite thin films

Authors: Predoi, D; Ghita, RV; Ungureanu, F; Negrila, CC; Vatasescu-Balcan, RA; Costache, M

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3831, DOI:

Thin films of hydroxyapatite (HAp) (Ca-10(PO4)(6)(OH)(2)) were vacuum deposited on different substrates (quartz and silver) in connection with biomedical applications. Characteristics of thin films were putted into evidence by (SEM) and (XPS) analysis. The FT-IR spectroscopy was performed on hydroxyapatite powder and thin films deposited on quartz. The deposition of HAp thin films presents good surface quality as a smooth and an adherent layer. The biological tests confirm the characteristics of these thin films as bioactive materials. The hydroxyapatite thin films supports have a micro cell configuration that allows them to be used for obtaining medical biocompatible supports.

139. Loss of phosphorous in silica-phosphate sol-gel films

Authors: Anastasescu, M; Gartner, M; Ghita, A; Predoana, L; Todan, L; Zaharescu, M; Vasiliu, C; Grigorescu, C; Negrila, C

Published: DEC 2006, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 40, 333, DOI: 10.1007/s10971-006-8775-y

Phosphosilicate films with 90%SiO2-10%P2O5 molar composition, derived from tetraethoxysilane as SiO2 precursor and triethylphosphate, triethylphosphite or phosphoric acid as P2O5 precursors were prepared using the sol-gel method. The films were deposited on glass and ITO coated glass supports. The influence of the type of P2O5 precursor, type of substrate and of the thermal treatment (200, 300 and 500 degrees C) on their structure and properties was studied. By spectroellipsometric and XPS measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when alkoxide were used, underlying that the mentioned precursors are not recommended for thin phosphosilicate films preparation. The phosphoric acid that forms chemical bond with silica network during the sol-gel process lead to better incorporation of P in the silica network as compared to the P-alkoxides.

140. XPS study of Ti/oxidized GaAs interface

Authors: Grita, RV; Logofatu, C; Negrila, C; Manea, AS; Cernea, M; Ciupina, V; Lazarescu, MF

Published: FEB 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 36, DOI:

X-Ray Photoelectron Spectroscopy (XPS) analysis was performed on Ti/oxidized GaAs. This interface is prepared by chemical etching in a mixture of reagents, followed by a vacuum deposition of a nanometer Ti layer. The surface sensitivity of XPS (typically 40-100 angstrom), makes the technique ideal for the measurements of oxidation states and oxide layer thickness on III-V compounds. The study of Ti/oxidized GaAs put into evidence a lack of stoichiometry at the semiconductor surface due to the presence of a volatile element (As). At the interface Ti/Oxide/n-GaAs common oxides are present: Ga2O3, As2O3 and As2O5, together with titanium oxide. The XPS spectra recorded on the sample surface sputtered with 5 keV Ar+ ions (in two steps: t = 15 min, t = 45 min) were analyzed using SDP subroutines program facilities. The As signal at the interface after t = 15 min plasma etching is related to GaAs, As2O3 and over 40% from a GaAs oxidation complex or due to intermetallic oxide of Ti. After the last plasma etching at the surface of GaAs the stoichiometry was demonstrated: the signal of As and Ga arises commonly from GaAs. It was remarked a broader titanium line profile, which arises from titanium oxide and from different intermediate states at the interface.

141. Studies of ohmic contact and Schottky barriers on Au-Ge/GaAs and Au-Ti/GaAs

Authors: Ghita, RV; Logofatu, C; Negrila, C; Manea, AS; Cernea, M; Lazarescu, MF

Published: DEC 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 3037, DOI:

Gallium Arsenide (GaAs) has increasingly become an important compound-semiconductor material suited for high speed digital circuits, microwaves and detectors for high energy physics. For the fabrication of ohmic contacts on GaAs (semi-insulating- SI) wafers with characteristics as: Cr doped, (100) oriented, and p similar to 10(6)similar to 10(7) Omega cm, has been used alloyed contact Au-Ge. The ohmic film was deposited in a high vacuum chamber (10(-8) Torr), on a plasma etched surface of GaAs, followed by a rapid thermal annealing (RTA) at 450 degrees C in low vacuum. For the fabrication of the rectifying contact-respectively the Schottky diode structure, we have used the same GaAs substrates. The wafers were degreased in a standard cleaning procedure, followed by a chemical etching. The Au-Ti contact has been deposited by thermal evaporation in vacuum (10(-6) torr) followed by a RFA procedure at 300-320 degrees C. The carrier transport mechanisms through M/S interface are strongly influenced by the doping concentration in the semiconductor and temperature. There are presented the experimental I-V characteristics for selected samples in dark and illumination conditions. Schottky barriers height on Au-Ti/GaAs was 0.7325 V in accord with mean values on n and p type GaAs (0.5-0.8 V). The aim of this work is to fabricate a competitive X-ray detector.

142. Surface chemistry of plasma deposited ZrC hard coatings

Authors: Balaceanu, M; Braic, M; Braic, V; Vladescu, A; Negrila, CC

Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2560, DOI:

X-ray Photoelectron Spectroscopy (XPS) was used to investigate the chemical state of ZrC coatings deposited by cathodic arc method. A chemistry model of the ZrC films has been proposed. It was pointed out that on the films surface a highly oxidized passive layer, containing also carbon and oxygen as contaminants, was formed. The film bulk was composed by a mixture of ZrC (the dominant phase), ZrO2 and free carbon.

143. Microchemical and mechanical characteristics of arc plasma deposited TiAlN and TiN/TiAlN coatings

Authors: Braic, M; Braic, V; Balaceanu, M; Pavelescu, G; Vladescu, A; Tudor, I; Popescu, A; Borsos, Z; Logofatu, C; Negrila, CC

Published: APR 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 676, DOI:

Single layer TiAlN and alternate TiN/TiAlN multilayered hard coatings were deposited on Si, plain carbon steel and high-speed steel substrates by the cathodic are technique. Chemical composition, phase composition, texture, Vickers microhardness, adhesion, bilayer period, sliding friction coefficient and wear resistance were investigated by XPS, EDX and XRD analyses, microhardness measurements, scratch and tribological tests.

144. Heusler bulk materials as targets for pulsed laser deposition: growth and characterisation

Authors: Manea, AS; Monnereau, O; Notonier, R; Guinneton, F; Logofatu, C; Tortet, L; Garnier, A; Mitrea, M; Negrila, C; Branford, W; Grigorescu, CEA

Published: FEB 15 2005, JOURNAL OF CRYSTAL GROWTH, 275, E1792, DOI: 10.1016/j.jcrysgro.2004.11.213

This work concerns the preparation and characterisation of homogeneous bulk Co2Mn (Si, Ge, Ga, Sn Sb0.8Sn0.2) to be used as targets for pulsed laser deposition of magnetic contacts for spintronic devices. The samples have been prepared by direct synthesis from elemental powders followed by vertical gradient freeze. Characterisation of their structural properties and compositional homogeneity was performed by X-ray diffraction and energy-dispersive X-ray spectroscopy combined with scanning electron microscopy. The results show one-phase for the Heusler alloys. The Curie temperatures of the samples have been measured by both thermogravimetric analysis and differential scanning calorimetry and are in a good agreement with the previously published values. The saturation magnetisation values are close to the values for single crystals. (C) 2004 Elsevier B.V. All rights reserved.

145. Bar-configuration in hall measurements with GaAs

Authors: Ghita, RV; Logofatu, C; Negrila, C; Lazarescu, MF; Manea, AS; Ciupina, V

Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 363, DOI:

The electrical and transport properties of GaAs crystals such as resistivity (rho), mobility (mu) and carrier concentration (n) depend on the purity and defects of a particular crystal. These parameters are normally obtained by performing a simple Hall effect analysis in a bar configuration. The technical procedure is connected with the design of appropriate contacts for Hall bar configuration. In order to ensure good ohmic contacts oil GaAs, thin metal layers of Au-Ge-Ni have been deposited in high vacuum followed by heat treatment in low vacuum. Hall effect measurement is important for checking the quality of the GaAs wafers. We analyzed various GaAs wafers with (100) and (110), orientation obtained by LEC and HB methods. The resistivity of the wafers varied from low resistivity, n-type doped crystals (n = 10(18) cm(-3)), to high resistivity crystals (n = 10(14) cm(-3)). This paper presents the data of Hall characterization of wafers cut from GaAs crystals grown by different methods (LEC, HB).

146. X-ray photoelectron spectroscopy study on n-type GaAs

Authors: Ghita, RV; Negrila, C; Manea, AS; Logofatu, C; Cernea, M; Lazarescu, MF

Published: DEC 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 863, DOI:

A surface characterization has been performed on n-type GaAs (Si: GaAs) samples by using X-ray photoelectron spectroscopy (XPS) technique in order to get information on the degree of surface contamination during the device processing steps. The GaAs samples were etched by "in situ" ion sputtering (Ar plasma) before and after carrying out the measurements. According to XPS measurements the native oxide layer on as-received surface contains As2O3, AS(2)O(5) and Ga2O3. Large amounts of C and O are also present at surface before plasma cleaning of surface: C-C bonds, chemisorbed oxygen atoms. The XPS spectra recorded on the surface sample sputtered with 5 keV Ar+ ions were analyzed using SDP subroutines program facilities. After the first sputtering step it was observed different shifts of the principal peaks of GaAs bonding and compounds together with a modification of the relative peak intensities. The C1s and O1s peak size decreased but remained still significant. The following sputtering steps lead to a drastically decrease of C and 0 peaks down to the noise level.

147. Role of vanadium oxide on the lithium silicate glass structure and properties