National Institute Of Materials Physics - Romania

Publications

860 articles found

351. The effect of H-2/Ar plasma treatment over photoconductivity of SiGe nanoparticles sandwiched between silicon oxide matrix

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

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 260, DOI:

The effect of room temperature hydrogen plasma treatment on the photoconductive properties of the SiO2 matrix containing SiGe nanoparticles is investigated. A considerable increase in photocurrent intensity is observed after plasma treatment. The increase is partly attributed to neutralization of dangling bonds around the nanoparticles and partly to passivation of non-radiative centers and defects in the matrix and at the nanoparticles-matrix interfaces.

352. MOS DOSIMETER BASED ON Ge NANOCRYSTALS IN HfO2

Authors: Palade, C; Slav, A; Lepadatu, AM; Stavarache, I; Dascalescu, I; Cojocaru, O; Stoica, T; Ciurea, ML; Lazanu, S

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 90, DOI:

Trilayer MOS capacitors gate HfO2 / floating gate of Ge nanocrystals in HfO2 / tunnel HfO2 / Si substrate were prepared in the aim to be used for the detection of ionizing radiation. Magnetron sputtering and rapid thermal annealing were used for their fabrication. Capacitance-voltage measurements showed that Ge nanocrystals are the most important charge storage centres in our structure. The possibility to use these trilayer MOS capacitors as dosimeters was investigated, and the sensitivity to alpha particle irradiation was extracted.

353. Origin and chemical composition of the amorphous material from the intergrain pores of self-assembled cubic ZnS:Mn nanocrystals

Authors: Stefan, M; Vlaicu, ID; Nistor, LC; Ghica, D; Nistor, SV

Published: DEC 31 2017, APPLIED SURFACE SCIENCE, 426, 350, DOI: 10.1016/j.apsusc.2017.07.172

We have shown in previous investigations that the low temperature collective magnetism observed in mesoporous cubic ZnS:Mn nanocrystalline powders prepared by colloidal synthesis, with nominal doping concentrations above 0.2 at.%, is due to the formation of Mn2+ clusters with distributed antifer romagnetic coupling localized in an amorphous phase found between the cubic ZnS:Mn nanocrystals. Here we investigate the composition, origin and thermal annealing behavior of this amorphous phase in such a mesoporous ZnS:Mn sample doped with 5 at.% Mn nominal concentration. Correlated analytical transmission electron microscopy, multifrequency electron paramagnetic resonance and Fourier transform infrared spectroscopy data show that the amorphous nanomaterial consists of unreacted precursor hydrated zinc and manganese acetates trapped inside the pores and on the surface of the cubic ZnS nanocrystals. The decomposition of the acetates under isochronal annealing up to 270 degrees C, where the mesoporous structure is still preserved, lead to changes in the nature and strength of the magnetic inter actions between the aggregated Mn2+ ions. These results strongly suggest the possibility to modulate the magnetic properties of such transition metal ions doped II-VI mesoporous structures by varying the synthesis conditions and/or by post-synthesis thermochemical treatments. (C) 2017 Elsevier B.V. All rights reserved.

354. Multiple polarization states in symmetric ferroelectric heterostructures for multi-bit non-volatile memories

Authors: Boni, GA; Filip, LD; Chirila, C; Pasuk, I; Negrea, R; Pintilie, I; Pintilie, L

Published: DEC 28 2017, NANOSCALE, 9, 19278, DOI: 10.1039/c7nr06354g

Here we report a ferroelectric capacitor structure obtained by alternating ferroelectric and insulator thin-film layers which allows an increase of up to 2(n) polarization states, with n the number of ferroelectric layers. Four and up to eight distinct, stable and independently addressed polarization states are experimentally demonstrated in this work. The experimental findings are supported by a theoretical model based on the Landau-Ginzburg-Devonshire theory. The key parameter is the change in the strain conditions of ferroelectric layers induced by the insulating separator. Notably, the 2(n) increase in the storage capacity can be achieved without major changes in the present technology used for FeRAM devices. The test structures demonstrate very good memory characteristics such as retention and fatigue, opening the way towards the design of high density ferroelectric memories.

355. New ways to use the red mud waste as raw material for inorganic-organic hybrid hydrogels

Authors: Sandu, T; Sarbu, A; Zavoianu, R; Spatarelu, CP; Florea, M; Bradu, C; Mara, EL; Dragut, DV; Alexandrescu, E; Zaharia, A; Radu, AL

Published: DEC 10 2017, , DOI: 10.1016/j.minpro.2017.11.005

356. 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.

357. Transparent thin films of indium tin oxide: Morphology-optical investigations, inter dependence analyzes

Authors: Prepelita, P; Filipescu, M; Stavarache, I; Garoi, F; Craciun, D

Published: DEC 1 2017, APPLIED SURFACE SCIENCE, 424, 373, DOI: 10.1016/j.apsusc.2017.02.106

Using a fast and eco-friendly deposition method, ITO thin films with different thicknesses (0.5 mu m-0.7 mu m) were deposited on glass substrates by radio frequency magnetron sputtering technique. A comparative analysis of these oxide films was then carried out. AFM investigations showed that the deposited films were smooth, uniform and having a surface roughness smaller than 10 nm. X-ray diffraction investigations showed that all samples were polycrystalline and the grain sizes of the films, corresponding to (222) cubic reflection, were found to increase with the increasing film thickness. The optical properties, evaluated by UV-VIS-NIR (190-3000 nm) spectrophotometer, evidenced that the obtained thin films were highly transparent, with a transmission coefficient between 90 and 96%, depending on the film thickness. Various methods (Swanepoel and Drude) were employed to appreciate the optimal behaviour of transparent oxide films, in determining the dielectric optical parameters and refractive index dispersion for ITO films exhibiting interference patterns in the optical transmission spectra. The electrical conductivity also increased as the film thickness increased. (C) 2017 Elsevier B.V. All rights reserved.

358. Floating zone partial re-melting of B4C infiltrated with molten Si

Authors: Solodkyi, I; Bogomol, I; Loboda, P; Batalu, D; Vlaicu, AM; Badica, P

Published: DEC 1 2017, CERAMICS INTERNATIONAL, 43, 14725, DOI: 10.1016/j.ceramint.2017.07.203

Green compacts of B4C or B4C added with 1 vol% graphite were infiltrated with molten Si and subsequently were subject of processing by floating zone partial re-melting (FZPR). In FZPR only the low temperature fusible component, in this case Si, is melted. A fully dense B4C-based ceramic is obtained. It contains free-Si, SiC and B4C. In the center of the FZPR ceramic without graphite addition, the amount of Si is decreased when compared to the infiltrated material. Some impurity elements such as Al, Fe, or Ti detected in the raw B4C powder are preferentially gathered at the edges of the sample. In the sample added with graphite, formation of a high amount of SiC in the infiltrated material hinders Si shift from the center to the edges. The pulling rate and the particle size of the B4C raw powders are also important. It is recognized that sintering of powders larger than 10-20 gm is usually difficult: our approach is demonstrated to be suitable for processing of B4C powders with a very different particle size, from 10 to 250 gm. The FZPR ceramic had a Vickers hardness of 9-38 GPa depending on location of the indentation imprint and on the sample. A tensile strength of 114-188 MPa that is up to about 2-3 times higher than for the infiltrated material was recorded. Work indicates that the proposed processing approach offers extended control possibilities towards fabrication of new composite materials not available by traditional technologies.

359. Enhancement of the electroluminescence of organic light emitting devices based on Ir(ppy)(3) by doping with metallic and magnetic nanoparticles

Authors: Ciobotaru, CC; Ciobotaru, IC; Schinteie, G; Negrea, R; Polosan, S

Published: DEC 2017, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 72, 84, DOI: 10.1016/j.mssp.2017.09.019

Magnetic nanoparticles embedded in the active layer of the Organic Light Emitting Diodes (OLEDs) significantly increases the electroluminescence and the charge transport without influencing the transparency of these devices. A brief comparison was done in order to identify which parameter influences these properties, by comparing the CoFe2O4 magnetic nanoparticles with CoFe2 metallic magnetic nanoparticles, the latter one being obtained by thermal reduction in hydrogen of cobalt ferrite nanoparticles. CoFe2 have shown a better efficiency of the metallic nanoparticles where probably the main advantage is the higher magnetization property instead of the coercive field. Concerning the charge transport across the OLEDs, these nanoparticles reduce the electron injection, acting as filling traps, which directly increases the electroluminescence and the current at the same voltage.

360. Structure, transition temperature, and magnetoresistance of titanium-doped lanthanum barium manganite epilayers onto STO 001 substrates

Authors: Galca, AC; Oumezzine, M; Leca, A; Chirila, CF; Kuncser, V; Kuncser, A; Ghica, C; Pasuk, I; Oumezzine, M

Published: OCT 30 2017, APPLIED PHYSICS LETTERS, 111, DOI: 10.1063/1.4998011

We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room temperature, which is one of the operating requirements for many applications. It is shown that La0.67Ba0.33Ti0.02Mn0.98O3 epilayers obtained by pulsed laser deposition onto (001) SrTiO3 single crystal substrates exhibit the highest MRE, Delta R/R(H) approximate to 150% or Delta R/R(0) approximate to 60% under 5 T, at 300 K, a temperature near to the corresponding Curie temperature (T-C). Both doping with a tiny amount of titanium and induced stress due to lattice mismatch between the thin film and the substrate contribute to a decrease in T-C as compared to the pristine compound and therefore to the decrease in the temperature where the highest MRE is recorded. Published by AIP Publishing.