National Institute Of Materials Physics - Romania

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5781 articles found

4011. Quantum confinement in nanocrystalline silicon

Authors: Ciurea, ML

Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2346, DOI:

Quantum confinement effects in different kinds of nanocrystalline silicon systems are experimentally and theoretically investigated. Porous silicon structured as a nanowire network and silicon nanodots embedded in amorphous silicon dioxide are studied. The main quantum confinement effect in both cases is represented by the appearance of new energy levels in the silicon band gap. The corresponding energies can be experimentally determined from the current - temperature characteristics, which show an Arrhenius-like behavior. The curves present several activation energies between liquid nitrogen temperature and room temperature. The energy levels can be evaluated from a quantum well model. The fundamental level is located at the top of the valence band. The change of the activation energy is then related with the filling of the levels. The ratios of the consecutive activation energies in the current - temperature characteristics prove that the excitation undergoes the angular momentum conservation law imposed by the applied electric field. The estimation of the mean size of the nanocrystals from the values of the activation energies is in good agreement with the microstructure investigations performed on the samples. The confinement levels are also in good agreement with the photoluminescence measurements..

4012. Ordering of the creeping vortex system in Bi2Sr2CaCu2O8+delta single crystals at low temperatures

Authors: Miu, L

Published: OCT 2005, PHYSICAL REVIEW B, 72, DOI: 10.1103/PhysRevB.72.132502

Zero-field-cooling magnetization relaxation measurements performed on Bi2Sr2CaCu2O8+delta single crystals in the low-temperature domain, with the external magnetic field oriented parallel to the c axis, reveal the ordering of the creeping vortex system due to the macroscopic currents induced in the sample. This explains many apparently conflicting results concerning the vortex phase diagram of disordered high-temperature superconductors, which have led to the dichotomy elastic vortex glass-plastic vortex assembly for the vortex phase at high magnetic fields.

4013. NRBS, RBS, TEM and SAED characterisation of sol-gel PZT films

Authors: Pantelica, D; Vasiliu, F; Ionescu, P; Negoita, F

Published: OCT 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 240, 404, DOI: 10.1016/j.nimb.2005.06.166

TEM-SAED investigations were performed on PZT films, to elucidate the role of pyrolysis conditions on orientation selection. For short pyrolysis, occurrence of the metastable fluorite and the interfacial PtxPb template layer are the factors inducing the (111) PZT orientation. For advanced pyrolysis, the TiO2 interfacial layer could be responsible for (100) PZT strong orientation. To further investigate the stoichiometry of PZT and interfacial layers, we performed heavy ion RBS and NRBS measurements. Only a substoichiometric TiO2-x layer is found for the short pyrolized film whereas two Ti and O rich layers were observed for advanced pyrolysis. The thicker oxygen rich TiO2-x bottom layer, observed by TEM and NRBS analysis, could lead to (100) texture, observed for oxidizing conditions at the interface during pyrolysis. (c) 2005 Elsevier B.V. All rights reserved.

4014. Properties of high-porosity sol-gel derived indium-tin oxide films

Authors: Stoica, TF; Gartner, M; Stoica, T; Losurdo, M; Teodorescu, VS; Blanchin, MG; Zaharescu, M

Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2358, DOI:

Indium-tin oxide (ITO) sol-gel films have been obtained with the void concentration up to 50%. The films are nanostructured with nanocrystals of In2O3:Sn and nanovoids. The information obtained from derivative thermo-gravimetry was used to design the annealing program for ITO film formation with a high void concentration. Multilayer films were obtained by successive deposition. The thickness of one layer was about 9 nm. By successive depositions, the void density of the film is reduced. Quantitative analysis of the void density has been performed by spectroscopic ellipsometry. The conductivity of the films can be varied in a large range by annealing in vacuum or in air, at temperature higher than 200 degrees C.

4015. Optical and electronic properties of the aluminophosphate glasses doped with 3d-transition metal ions

Authors: Elisa, M; Grigorescu, CEA; Vasiliu, C; Bulinski, M; Kuncser, V; Predoi, D; Filoti, G; Meghea, A; Iftimie, N; Giurginca, M

Published: OCT 2005, REVIEWS ON ADVANCED MATERIALS SCIENCE, 10, 374, DOI:

Aluminophosphate glasses doped with Fe, Mn, and Cr have been obtained by a wet non-conventional method. Structural information was provided by IR absorption spectra in the range 2000-500 cm(-1). The optical behaviour (transmission and refractive index) of the samples has been studied by UV-VIS-NIR spectroscopy. The Fe valence state and the local coordination were also analysed via Fe-57 Mossbauer spectroscopy, whose data revealed the redox equilibrium in the Fe-doped glasses according to the redox potentials of the transition ions.

4016. Electron beam irradiation for biological decontamination of Spirulina platensis

Authors: Brasoveanu, M; Nemtanu, M; Minea, R; Grecu, MN; Mazilu, E; Radulescu, N

Published: OCT 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 240, 90, DOI: 10.1016/j.nimb.2005.06.093

The Cyanobacterium Spirulina is commercialized for its use in health foods and for therapeutic purposes due to its valuable constituents particularly proteins and vitamins. The aim of the paper is to study the Spirulina platensis behaviour when it is electron beam irradiated for biological decontamination. Microbial load, antioxidant activity, enzymatic inhibition, electron spin resonance (ESR) and UV-Vis spectra were measured for doses up to 80 kGy. The results were correlated with doses in order to find where decontamination is efficient, keeping the Spirulina qualities. (c) 2005 Elsevier B.V. All rights reserved.

4017. Field effects and surface states in second harmonic generation at n-GaAs(h k l) electrodes

Authors: Lazarescu, V; Scurtu, R; Lazarescu, MF; Santos, E; Jones, H; Schmickler, W

Published: SEP 5 2005, ELECTROCHIMICA ACTA, 50, 4836, DOI: 10.1016/j.electacta.2005.02.069

Second harmonic generation from n-doped GaAs(111)-A, GaAs(111)-B and GaAs(110) electrodes in sulfuric acid solution has been compared at an incident wavelength of 1064 nm over a potential range, where Faradaic process are excluded. In the p-in/p-out polarization configuration, the rotational anisotropy of the SH response reflects the symmetry of the crystal surface. The isotropic part of the response depends significantly on the applied electric field in the space-charge region, suggesting that the dominant part of the SH response is generated in the near-surface depletion region. The effects of the applied potential on the isotropic amplitude of the SH-signal show, however, that the high density of the surface/interface states at the Fermi level, revealed in impedance spectroscopy, may play an important role as well. (C) 2005 Elsevier Ltd. All rights reserved.

4018. Supported perovskites for total oxidation of toluene

Authors: Alifanti, M; Florea, M; Somacescu, S; Parvulescu, VI

Published: SEP 1 2005, , DOI: 10.1016/j.apcatb.2005.02.018

4019. Nanostructure and properties of Pb(Zr,Ti)O-3-Pb(Ni-1/3 Nb-2/3)O-3 piezoceramics

Authors: Dimitriu, E; Craciun, F; Ghica, C; Ramer, R

Published: SEP 2005, JOURNAL DE PHYSIQUE IV, 128, 143, DOI: 10.1051/jp4:2005128022

Piezoceramics with composition 0.46 Pb(Zr0.3Ti0.7)O-3 - 0.53 Pb(Ni1/3Nb2/3)O-3 have been synthesized by solid-state reaction at different temperatures. The density varied between 8.05-8.1 g/cm(3). The sintered samples have been chemically electroded with Ni and poled at 220C under an electric field of 3 kV/cm. The XRD spectra confirmed the formation of tetragonal crystalline phase with a tetragonal distortion c/a = 1.0125 which was decreased from a value of about 1.042 that corresponds to pure PZT with y = 0.3. Some minor traces of non-reacted precursor oxides such as Nb2O5 have been also found. TEM results confirmed the formation of tetragonal phase and revealed crystal grains with domains of different size, slightly disoriented from each other. Dielectric measurements performed between 20 degrees C and 300 degrees C at different frequencies between 100 Hz and 1 MHz revealed a broad dielectric anomaly at T-m = 118 degrees C (200Hz) which shifts to 127 degrees C at I MHz driving frequency. A dependence of T-m on sintering temperature has been observed. A thermal hysteresis is also found on heating and cooling. This shows that the samples present both relaxor and ferroelectric characteristics. High values of the dielectric constant are found both at room temperature (about 5000) and at T-m (about 18000). The dependence of dielectric and piezoelectric constants on sintering temperature has been found.

4020. Morphological and optical investigation of lead zirconate titanate (20/80) ultra-thin films

Authors: Boerasu, I; Watts, BE; Leccabue, F

Published: SEP 2005, INFORMACIJE MIDEM-JOURNAL OF MICROELECTRONICS ELECTRONIC COMPONENTS AND MATERIALS, 35, 113, DOI:

Ultra-thin (< 20 nm) lead zirconate-titanate films with Zr/Ti ratio of 20/80 have been deposited on single crystal MgO substrates by sol-gel techniques. Atomic force microscopy reveals a smooth surface consisting of pyramids or domes. The surface morphology is discussed in terms of a double-step growth process: epitaxial growth in the early stages followed by growth on screw dislocations. Measurements of the optical extinction spectra for the PZT (20/80) ultra-thin films are reported and modelled to extract the data on the energy gap.