National Institute Of Materials Physics - Romania

Publications

5781 articles found

3081. HIGH PERFORMANCE COMPUTING INFRASTRUCTURE FOR MATERIALS SCIENCE

Authors: Chihaia, V; Slusanschi, E; Herisanu, A; Palade, P; Tapus, N

Published: NOV-DEC 2010, REVUE ROUMAINE DE CHIMIE, 55, +, DOI:

Computer Material Science is a branch of material sciences that uses theoretical concepts and models from chemistry, physics, geology, mineralogy, as well as biology and includes them into software applications in order to calculate the structure and the properties of molecules, gases, liquids, soft and condensed matter. This paper presents the estimated performances of the HPC-ICF cluster of the Institute of Physical Chemistry "Ilie Murgulescu" of the Romanian Academy and the NCIT-UPB Cluster developed by the Computer Science Department of the University Politehnica of Bucharest, with the run in the parallel mode on these systems of the HPL - High Performance Linpack Benchmark as well as of the electronic structure codes GAMESS and ONETEP. The results of the study show that both clusters break the Teraflop barrier, thus making available a valuable tool for the Romanian scientific community in Computing Materials Science.

3082. 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

3083. Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings (vol 255, pg 9132, 2009)

Authors: Stan, GE; Morosanu, CO; Marcov, DA; Pasuk, I; Miculescu, F; Reumont, G

Published: DEC 15 2009, APPLIED SURFACE SCIENCE, 256, 1617, DOI: 10.1016/j.apsusc.2009.08.083

3084. Photo-degradation activity of sputter-deposited nitrogen-doped titania thin films

Authors: Apetrei, R; Catrinescu, C; Mardare, D; Teodorescu, CM; Luca, D

Published: DEC 15 2009, THIN SOLID FILMS, 518, 1043, DOI: 10.1016/j.tsf.2009.05.068

Various approaches have been reported during the last decade to enhance the photo-catalytic and super-hydrophilic characteristics of the intrinsic TiO2 materials. Results on the photo-degradation activity of RF-sputtered nitrogen-doped titania thin films are presented here with respect to two environmental pollutants in gas- and liquid phases, as a function of dopant concentration. This study was accomplished by monitoring the time dependence of pollutant concentration in contact with the films, both under UV and solar light illumination. The synergic effects of surface morphology, crystalline and electronic structure of the materials are discussed in relation with the observed experimental facts. The results presented here show a close correlation between the oxidative power of the films and their previously reported wettability features. (C) 2009 Elsevier B.V. All rights reserved.

3085. Q-switched Nd lasers pumped directly into the F-4(3/2) emitting level

Authors: Pavel, N; Dascalu, T; Salamu, G; Sandu, O; Leca, A; Lupei, V

Published: DEC 15 2009, OPTICS COMMUNICATIONS, 282, 4754, DOI: 10.1016/j.optcom.2009.08.067

The influence of the direct pumping into the F-4(3/2) emitting level on the output characteristics of continuous-wave (CW) pumped, passively or actively (acoustooptic, AO) Q-switched Nd lasers is discussed. In case of passive Q-switching by Cr4+: YAG saturable absorber (SA) crystal, the change of pumping wavelength from 0.81 mu m into the highly-absorbing F-4(5/2) level to 0.88 mu m into the F-4(3/2) level of Nd does not modify the energy of the Q-switch pulse, but increases the pulse repetition rate and the laser average power for the same absorbed pump power. This is demonstrated with 0.81 and 0.88 gm CW laser diode-pumped Nd:YAG and Nd-vanadate lasers with average output power in the watt-level range at 1.06 mu m. The effect is explained by the control of passive Q-switching by the intracavity photon flux that is influenced by the pump wavelength and by the initial transmission of the SA crystal. On the other hand, it is discussed and experimentally proved that due to the possibility to control externally the frequency of switching, in case of the AO Q-switched Nd laser the change of the pump wavelength from 0.81 to 0.88 pm increases the pulse energy for a fixed frequency, leading to a corresponding increase of the average laser power. (C) 2009 Elsevier B.V. All rights reserved.

3086. Carrier relaxation dynamics in self-assembled semiconductor quantum dots

Authors: Kurtze, H; Seebeck, J; Gartner, P; Yakovlev, DR; Reuter, D; Wieck, AD; Bayer, M; Jahnke, F

Published: DEC 2009, PHYSICAL REVIEW B, 80, DOI: 10.1103/PhysRevB.80.235319

Systematic time-resolved pump-probe studies with independent variation in pump and probe energies in combination with time-resolved photoluminescence measurements have been used to investigate the dynamics of carrier capture and carrier relaxation in self-assembled (In,Ga)As/GaAs semiconductor quantum dots. Even for weak excitation, where carrier-carrier scattering is less efficient, the lower-energy quantum-dot states are rapidly populated, whereas for increasing delay times between pump and probe pulses residual populations in the higher quantum-dot states are found. A quantum-kinetic description of the carrier interaction with LO phonons is used for a treatment beyond perturbation theory to include polaron effects and to account also for the non-Markovian dynamics. On this level, the theory for the carrier-phonon interaction confirms fast initial carrier relaxation that becomes incomplete for longer times and results in a nonthermal carrier population in the considered low-temperature regime.

3087. Tellurium based phase change materials

Authors: Velea, A

Published: DEC 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1987, DOI:

Phase change materials are the most promising materials for innovation in the computer memory industry. Of great importance is the understanding of the processes that take place during the switching from the high resistivity state to the low resistivity state. In this paper we have tried to find out the correlations between the crystallo-chemical parameters and the switching properties of these materials. The crystallo-chemical parameters, average electronegativity, and glass forming ability (n) over bar(k) over bar/(Z) over bar have been calculated for a large number of tellurium chalcogenides. The switching parameters have been correlated with the physical properties of these materials: resistivity, activation energy, and average electronegativity. Change of the chemical bonding during switching would be responsible for the outstanding properties of the phase change materials.

3088. 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.

3089. 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+.

3090. 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.