National Institute Of Materials Physics - Romania

Publications

5714 articles found

3011. ATOMIC STRUCTURE AND MAGNETIC PROPERTIES OF COBALT DOPED ZnO THIN FILMS PREPARED BY THE SOL-GEL METHOD

Authors: Neamtu, J; Georgescu, G; Malaeru, T; Gheorghe, NG; Costescu, RM; Jitaru, I; Ferre, J; Macovei, D; Teodorescu, CM

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 885, DOI:

The ability of a sol-gel route for the synthesis of cobalt doped ZnO (Zn 1-xCoxO, x = 0.04-0.11) films grown on Si (100) and glass substrates is investigated. A homogeneous and stable Zn (1-x) CoxO sol was prepared by dissolving zinc nitrate hexahydrate and cobalt acetate tetrahydrate in a PVP (polyvinylpyrrolidone) solution, followed by annealing at 800 degrees C. Local structure studies of the Zn1-xCoxO thin films by XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure) proved the co-existence of a few amount of small metal cobalt aggregates with Co in non-stoichiometric ConOm aggregates, with n > m, and m similar to 4. Low temperature magneto-optical Kerr effect (Faraday rotation) measurements of the magnetization versus field give a direct proof of a superparamagnetic behavior of the magnetic aggregates and allowed an estimate of the number of magnetically active atoms in Co aggregates, which is close to the number of Co excess atoms inferred from XANES and EXAFS considerations: n - m similar to 3 atoms per aggregate. To this main superparamagnetic phase, a weak ferromagnetic phase with coercitive field of similar to 50 Oe is superimposed, most probably due to metal cobalt nanoclusters.

3012. Magnetic Configuration and Relaxation in Iron Based Nano-Particles: A Mossbauer Approach

Authors: Kuncser, V; Schinteie, G; Alexandrescu, R; Morjan, I; Vekas, L; Filoti, G

Published: 2010, TRENDS IN NANOPHYSICS: THEORY, EXPERIMENT AND TECHNOLOGY, 314, DOI: 10.1007/978-3-642-12070-1_13

The difficulty to stabilize a definite crystalline structure or phase, due to a large gradient of defects along the particle diameter, is unfortunately specific to particles of nanometer size. Therefore, atypical spin configurations and magnetic anisotropies as well as enhanced magnetic relaxations via thermal excitations are expected in systems of fine nano-particles. The actual work reports on various possibilities for a comprehensive characterization of the magnetic configuration and magnetic relaxation mechanisms of nano-particles, by corroborating the powerful method of Mossbauer spectroscopy with complementary magnetic and structural techniques. The capabilities of temperature and field dependent Mossbauer spectroscopy to provide valuable information about spin blocking temperatures, effective anisotropy constants, amount of uncompensated spins inside of particle and magnetic phase composition are critically discussed for both powder like systems and nano-particles dispersed in different solvents.

3013. Mossbauer measurements on SnSe(2)

Authors: Bibicu, I; Lorinczi, A; Popescu, M

Published: 2010, , DOI: 10.1117/12.881773

Tin chalcogenides SnX(2) and SnX, where X = S, Se and Te present a particularly interest for their electronic properties and applications in gas sensors. The state of tin in these materials is important for understanding of the sensing effect and improvement of the sensor performances. Mossbauer spectroscopy is a widely used technique for the analysis of the local electronic structure or chemical bonding in solids. In this paper we applied Mossbauer technique for the investigation of bulk and thin films of SnSe(2) chalcogenide. The films of SnSe2 chalcogenide were obtained by the methods: PLD ("Pulsed laser deposition") and PED ("Pulsed electron deposition"). Mossbauer measurements were performed by transmission (TMS), respectively conversion electron spectroscopy (CEMS). By CEMS spectroscopy surfaces, coatings and thin films containing Sn can be studied on substrates and to various depths up to 1000 nanometers.

3014. 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.

3015. 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

3016. 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

3017. 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.

3018. 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.

3019. 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.

3020. 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.