National Institute Of Materials Physics - Romania

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860 articles found

641. TEMPERATURE DEPENDENCE OF CAPTURE COEFFICIENTS IN TRAPPING PHENOMENA

Authors: Lepadatu, AM; Stavarache, I; Lazanu, S; Iancu, V; Mitroi, MR; Nigmatulin, RR; Ciurea, ML

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 374, DOI:

The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian type and is in a good agreement with the experimental results.

642. HYDROGEN-PLASMA INDUCED PLATELETS AND VOIDS IN SILICON WAFERS

Authors: Ghica, C; Nistor, LC; Mironov, B; Vizireanu, S

Published: 2010, ROMANIAN REPORTS IN PHYSICS, 62, 340, DOI:

Silicon wafers have been submitted to hydrogen RF-plasma treatment in various experimental conditions The hydrogen RF-plasma treatment on Si wafers induces two kinds of effects surface corrugation and formation of structural defects below the wafer surface The structural defects resulted after the plasma treatments have been investigated by conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) techniques The specificity of the induced extended defects due to hydrogen decoration has been emphasized

643. Quantum Confinement in Nanometric Structures

Authors: Ciurea, ML; Iancu, V

Published: 2010, NEW TRENDS IN NANOTECHNOLOGY AND FRACTIONAL CALCULUS APPLICATIONS, +, DOI: 10.1007/978-90-481-3293-5_5

This paper discusses the quantum confinement effects in nanometric structures that form low dimensional systems. In such systems, each surface/interface acts like a potential barrier, i.e. the wall of a quantum well, generating new energy levels. These levels are computed in a model that uses the approximation of the infinite rectangular quantum wells. The model is adapted for 2D, 1D and 0D systems, respectively. Different applications are discussed. The differences between the model results and the experimental data are proved to be of the same order of magnitude as the differences between the levels computed within the frame of infinite and finite quantum well approximations.

644. Lattice defect assisted incorporation of Mn2+ ions in cubic II-VI semiconductor quantum dots

Authors: Nistor, SV; Stefan, M; Nistor, LC; Ghica, D; Mateescu, CD; Barascu, JN

Published: 2010, 11TH EUROPHYSICAL CONFERENCE ON DEFECTS IN INSULATING MATERIALS (EURODIM 2010), 15, DOI: 10.1088/1757-899X/15/1/012024

Electron paramagnetic resonance spectra from substitutional Mn2+ ions in quantum dots of cubic ZnS with tight size distribution centred at 2 nm were recorded in the 9.8 GHz and 34 GHz frequency bands. Their quantitative analysis with line shape simulation and fitting computer programs accounting for both forbidden transitions and line broadening effects demonstrate the presence of a local axial distortion attributed to a neighbouring extended planar stacking defect. The presence of such extended lattice defects, confirmed from a high resolution transmission electron microscopy study on presently investigated cubic ZnS quantum dots, seems to be essential in the incorporation and localization of Mn2+ activating ions in other cubic II-VI semiconductor quantum dots as well.

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

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

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

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

646. Study of the ground multiplet of Kramers rare earth ions in solid matrices by multifrequency electron paramagnetic resonance spectroscopy: Nd3+ in PbWO4 single-crystals (vol 131, 034505, 2009)

Authors: Popescu, FF; Bercu, V; Barascu, JN; Martinelli, M; Massa, CA; Pardi, LA; Stefan, M; Nistor, SV; Nikl, M; Bohacek, P

Published: DEC 28 2009, JOURNAL OF CHEMICAL PHYSICS, 131, DOI: 10.1063/1.3280223

647. Semiconductor detectors for high radiation fields: microscopic processes in materials and the control of device parameters

Authors: Lazanu, S; Ciurea, ML; Lazanu, I

Published: DEC 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 2154, DOI:

The knowledge of the effects of radiation in semiconductor devices, in particular in detectors, represents an important and active field of research. The influence of isovalent impurities, carbon and germanium, on the radiation damage of silicon for detectors is investigated in the frame of a quantitative phenomenological model for defect kinetics, developed previously by the authors. The concentrations of defects induced by irradiation in materials with different doping levels are calculated, as well as the leakage current and effective carrier concentrations in p-n junction detectors made from these materials. The beneficial effect of Ge on the radiation damage of silicon is deduced.

648. Atomic force microscopy study of TiO2 sol-gel films thermally treated under NH3 atmosphere

Authors: Trapalis, C; Todorova, N; Anastasescu, M; Anastasescu, C; Stoica, M; Gartner, M; Zaharescu, M; Stoica, T

Published: OCT 1 2009, THIN SOLID FILMS, 517, 6247, DOI: 10.1016/j.tsf.2009.02.070

Multilayered TiO2 films were obtained by sol-gel and dipping deposition on quartz substrate followed by thermal treatment under NH3 atmosphere. In an attempt to understand the close relationship between microstructural characteristics and the synthesis parameters, a systematic research of the structure and the morphology of NH3 modified TiO2 sol-gel films by XRD and Atomic Force Microscopy is reported. The surface morphology has been evaluated in terms of grains size, fractal dimension and surface roughness. For each surface, it was found a self-similar behavior (with mean fractal dimension in the range of 2.67-3.00) related to an optimum morphology favorable to maintain a nano-size distribution of the grains. The root mean square (RMS) roughness of the samples was found to be in the range of 0.72-6.02 nm. (C) 2009 Elsevier B.V. All rights reserved.

649. Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Authors: Secu, M; Secu, CE; Polosan, S; Aldica, G; Ghica, C

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1872, DOI: 10.1016/j.jnoncrysol.2009.04.062

Transparent oxyfluoride glass-ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing Eu-doped CaF2 nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF2 nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu3+ ion along with annealing time which is consistent with the Eu3+ environment evolving from a glassy to a crystalline state. (C) 2009 Elsevier B.V. All rights reserved.

650. Ultrafine particles of ZnGa2O4 obtained by solution combustion and complexation methods

Authors: Gingasu, D; Mindru, I; Marinescu, G; Patron, L; Ghica, C

Published: JUL 29 2009, JOURNAL OF ALLOYS AND COMPOUNDS, 481, 895, DOI: 10.1016/j.jallcom.2009.03.193

Two soft chemistry routes - complexation and solution combustion - are explored to obtain the zinc gallate spinel ZnGa2O4. Three types of complexes, namely: (NH4)(2)[ZnGa2(C4O6H4)(4)(OH)(2)]center dot 4H(2)O, [ZnGa2(NH2CH2COOH)(4.5)](NO3)(8)center dot 4H(2)O and [ZnGa2(CO(NH2)(2))(7)](NO3)(8)center dot 9H(2)O have been synthesized and characterized by IR and UV-vis spectroscopy. Zinc gallate spinels obtained by decomposition of these compounds have been investigated by XRD spectra, analytic electronic microscopy and photoluminescence spectroscopy. Zinc gallate spinels exhibited blue emission spectra in the wavelength range of 400 nm-450 nm. (C) 2009 Elsevier B.V. All rights reserved.