National Institute Of Materials Physics - Romania

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5714 articles found

3021. Submicron wires with nanosized grain structure

Authors: Sima, M; Ion, L; Antohe, S; Vasile, E

Published: DEC 2009, SUPERLATTICES AND MICROSTRUCTURES, 46, 839, DOI: 10.1016/j.spmi.2009.09.010

Recent results have shown that size-effects in nanostructured materials may enable much more efficient thermoelectric devices. In this paper, the electrochemical preparation of Bi(1.95)Te(2.7)Se(0.35) and Bi(2.15)Te(2.55)Se(0.3) submicron wires arrays with nanosized grain structure is reported. X-ray diffraction (XRD) analysis has indicated the presence of nanosized crystallites in the structure of the wires; high resolution transmission electron microscopy (HRTEM) investigations have confirmed the formation of crystallites with geometrical dimensions of 5-14 nm and random orientations in the structure of these wires. These wires were further analyzed by field emission scanning electron microscopy (FESEM). The measurement of the transport properties showed that a highly degenerate semiconductor with a large thermopower (-125 mu V K(-1) at 300 K) and a low resistivity was obtained. (C) 2009 Elsevier Ltd. All rights reserved.

3022. Optical and EPR investigations of the thermal treatment effects on YVO4 nanocrystals

Authors: Georgescu, S; Cotoi, E; Voiculescu, AM; Toma, O; Grecu, MN; Borca, E; Hodorogea, S

Published: DEC 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1387, DOI:

YVO4 nanocrystals doped with Eu (5 at.%) or Gd (1 at.%) were synthesized by precipitation method and annealed at various temperatures between 60 degrees C and 900 degrees C. The average size (coherence domain) of the YVO4 and nanocrystals, estimated from X-ray diffraction measurements, varies from similar to 7 nm to similar to 60 nm, function of the annealing temperature. The morphological transformations produced by thermal treatments in YVO4 nanocrystals were monitored using optical spectroscopy with Eu3+ as probe and EPR spectroscopy, the paramagnetic probe being Gd3+.

3023. Fabrication of submicrometer periodic structures using interference lithography and two-layer chalcogenide photoresist

Authors: Indutnyi, IZ; Popescu, M; Lorinczi, A; Sava, F; Min'ko, VI; Shepeliavyi, PE; Dan'ko, VA

Published: DEC 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1971, DOI:

Technological process of interference lithography using two-layer chalcogenide photoresist were investigated. Top As(40)S(30)Se(30) layer is photoresist with a high selectivity and can be used for recording of interference pattern and formation of first lithographic mask. Second, more thick As(4)Ge(30)S(66) layer, almost is not sensitive to light, but dissolves in weak (0.05%) water solution of KOH. That, optimizing the etchant solutions for both layers, exposure and time of etching it is possible to carry out the technological process of formation of the lithographic mask with high modulation and with the groove form close to rectangular. This technology has been used for the fabrication of one- and two-dimensional periodic structures. Using two layer As(40)S(30)Se(30)-As(4)Ge(30)S(66) photoresist, we have fabricated the diffraction gratings and two-dimensional periodic structures with elements of submicron size. Relief parameters and diffractions properties of the obtained structures and their dependence on etching time are studied.

3024. Matrix-assisted photo-amorphization effect in As40S30Se30 films with silver

Authors: Popescu, M; Petkov, K; Sava, F; Taseeva, J; Lorinczi, A; Velea, A

Published: DEC 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 2003, DOI:

Matrix assisted photo-amorphization effect has been observed in thin chalcogenide films of composition As40S30Se30 deposited by thermal evaporation on silicon wafer substrate covered by silver. The initial films contain Ag2S and Ag4SeS crystallites embedded in an amorphous matrix. Illumination by a cold light halogen lamp induces the disappearance of the crystalline fraction and leads to significant changes in the diffraction pattern of the amorphous films.

3025. Growth and optical characteristics of coumarin 6 doped potassium hydrogen phthalate (KAP) crystals

Authors: Enculescu, M

Published: DEC 2009, OPTICAL MATERIALS, 32, 285, DOI: 10.1016/j.optmat.2009.08.002

Single-crystals of potassium hydrogen phthalate (KAP) doped with coumarin 6 (C6) were grown by solution evaporation technique. Powder X-ray diffraction. optical transmission and luminescence measurements were performed. The structure and morphology of the KAP crystals are not changed with the incorporation of the dye. Transparency of the dye-doped crystals is suited for non-linear optical (NLO) applications and UV cut-off is not changed when compared with the pure KAP crystals. The dye-doped crystals present an absorption band at 350 nm while the growth solution exhibits a peak at 400 nm. The doped crystals have a strong emission band at 450 nm that is excited at 350 nm and the second harmonic generating (SHG) properties are demonstrated using luminescence measurements. (C) 2009 Elsevier B.V. All rights reserved.

3026. Vibrational properties of the electrochemically synthesized polyindole/single-walled carbon nanotubes composite

Authors: Baibarac, M; Baltog, I; Scocioreanu, M; Lefrant, S; Mevellec, JY

Published: DEC 2009, SYNTHETIC METALS, 159, 2555, DOI: 10.1016/j.synthmet.2009.09.010

Electrochemical polymerization of indole in a LiClO4/CH3CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm(-1) is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH4OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect. (C) 2009 Elsevier B.V. All rights reserved.

3027. 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.

3028. Radiation-induced point- and cluster-related defects with strong impact on damage properties of silicon detectors

Authors: Pintilie, I; Lindstroem, G; Junkes, A; Fretwurst, E

Published: NOV 21 2009, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 611, 68, DOI: 10.1016/j.nima.2009.09.065

This work focuses on the investigation of radiation-induced defects responsible for the degradation of silicon detector performance. Comparative studies of the defects induced by irradiation with Co-60-gamma rays, 6 and 15 MeV electrons, 23 GeV protons and reactor neutrons revealed the existence of point defects and cluster-related centers having a strong impact on damage properties of Si diodes. The detailed relation between the "microscopic" reasons as based on defect analysis and their "macroscopic" consequences for detector performance is presented. In particular, it is shown that the changes in the Si device properties (depletion voltage and leakage current) after exposure to high levels of Co-60-gamma doses can be completely understood by the microscopically investigated formation of two point defects, a deep acceptor and a shallow donor, both depending strongly on the oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease (increase) the originally observed damage effects as seen by the changes of the depletion voltage and these effects are known as "beneficial" and "reverse" annealing, respectively. A group of three cluster-related defects, revealed as deep hole traps, proved to be responsible specifically for the reverse annealing. Their formation is not affected by the oxygen content or silicon growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions. (C) 2009 Elsevier B.V. All rights reserved.

3029. Local environment of vanadium in V/Al/O-mixed oxide catalyst for propane ammoxidation: Characterization by in situ valence-to-core X-ray emission spectroscopy and X-ray absorption spectroscopy

Authors: Safonova, OV; Florea, M; Bilde, J; Delichere, P; Millet, JMM

Published: NOV 15 2009, , DOI: 10.1016/j.jcat.2009.09.014

3030. AlN on silicon based surface acoustic wave resonators operating at 5 GHz

Authors: Neculoiu, D; Muller, A; Deligeorgis, G; Dinescu, A; Stavrinidis, A; Vasilache, D; Cismaru, AM; Stan, GE; Konstantinidis, G

Published: NOV 5 2009, ELECTRONICS LETTERS, 45, 1197, DOI: 10.1049/el.2009.2520

The fabrication and characterisation of surface acoustic wave resonators operating in the gigahertz frequency range are presented. The devices were fabricated on thin AlN layers deposited by magnetron sputtering on high resistivity (100) oriented silicon substrates. Using direct writing e-beam lithography, well defined interdigital transducers with 300 nm finger width and spacing have been obtained. On-wafer microwave measurements have demonstrated a narrow bandstop frequency characteristic with high rejection at approximately 5 GHz and an electromechanical coupling coefficient of 0.53%.