National Institute Of Materials Physics - Romania

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5781 articles found

3041. 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.

3042. ON THE ELECTRICAL CONDUCTIVITY IN Al:ZnO LAYERS; EXPERIMENTAL INVESTIGATION AND A THEORETICAL APPROACH

Authors: Plugaru, R; Plugaru, N; Mihaiu, S; Vasile, E

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 348, DOI:

Multi-layered AlZnO thin films, with wurtzite - type structure and thickness up to 120 nm, as determined by x-ray diffraction and HRTEM, were grown on Si-SiO2 and glass substrates by the sol-gel method. Fluorescence spectroscopy measurements show that 0.5 at. % Al doping determines a blue shift of the emission band observed at 387nm in the undoped material. The room temperature conductivity increases when the number of layers increases, to reach a value of 3.70 (Omega.m)(-1) for a ten layer film. Results obtained by total energy first principles calculations performed on systems with chemical disorder are discussed in relationship with experimental data to account for the effect of Al on the conductivity.

3043. OPTICAL AND MOSSBAUER SPECTROSCOPY STUDIES ON YVO(4):Eu NANOPHOSPHOR

Authors: Voiculescu, AM; Cotoi, E; Toma, O; Georgescu, S; Constantinescu, S; Bibicu, I

Published: 2010, ROMANIAN REPORTS IN PHYSICS, 62, 127, DOI:

Using europium as sensitive probe for both fluorescence and Mossbauer spectroscopy the morphological changes (local symmetry, covalence, ionicity) induced by the thermal treatments in the YVO(4) nanocrystals (synthesized by direct precipitation method) are put into evidence.

3044. 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

3045. STRUCTURES EXHIBITING LEFT-HANDED PROPERTIES IN MICROWAVE RANGE

Authors: Banciu, MG; Ioachim, A; Militaru, N; Lojewski, G; Ramer, R

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 294, DOI:

New distributed multilayer microstrip structures are investigated in microwaves. The amplitude and phase responses are analyzed for different geometrical parameters, number of cells and dielectric constants of the dielectric layers. It is shown that the proposed structures exhibit left-handed properties in a frequency range near the resonance.

3046. Optical and morphologic properties of YVO4:Eu phosphor

Authors: Georgescu, S; Voiculescu, AM; Cotoi, E; Toma, O; Gheorghe, L; Achim, A; Matei, C; Enculescu, I; Matei, E; Osiac, M

Published: 2010, ROMOPTO 2009: NINTH CONFERENCE ON OPTICS: MICRO- TO NANOPHOTONICS II, 7469, DOI: 10.1117/12.866769

In this paper we present new results concerning the optical and morphologic properties of YVO4:Eu red nanophosphor prepared by a precipitation method and subsequently annealed in air at various temperatures. We monitored the morphologic changes induced by the thermal treatments using the optical spectroscopy (reflectance and luminescence spectra), XRD and electron microscopy. The annealing leads to an increase of the particle size and improvement of the order of the crystalline lattice of YVO4. The annealing at 800 degrees C produces the sample with the highest luminescence intensity.

3047. BIOREACTIVITY EVALUATION IN SIMULATED BODY FLUID OF MAGNETRON SPUTTERED GLASS AND GLASS-CERAMIC COATINGS: A FTIR SPECTROSCOPY STUDY

Authors: Stan, GE; Popa, AC; Bojin, D

Published: APR-JUN 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 566, DOI:

In this study, Fourier Transform Infrared Spectroscopy (FTIR) in Attenuated Total Reflectance mode was employed as main characterization technique to investigate the reaction mechanisms in vitro (SBF) of bioglass and glass-ceramic sputtered coatings. Two bioglass compositional systems are compared in order to gain more information regarding their in vitro bioreactivity. Important correlations between the concentration of non-bridging silicon-oxygen (Si-O-NBO) groups and the content of network modifiers were found. FTIR revealed that the high concentrations of Si-O-NBO groups are promoting the enhancing of coatings' reactivity. This information could be very useful for the development and tailoring of new bioactive glasses with an optimum biological behaviour. By varying the compositional features and the structural state, the sputtered glassy coatings exhibited different in vitro behaviour: inertness, resorbability and bioactivity.

3048. One-Pot Synthesis of Menthol Catalyzed by a Highly Diastereoselective Au/MgF2 Catalyst

Authors: Negoi, A; Wuttke, S; Kemnitz, E; Macovei, D; Parvulescu, VI; Teodorescu, CM; Coman, SM

Published: 2010, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 8138, DOI: 10.1002/anie.201002090

3049. BEHAVIOR OF THE MAIN PROPETIES OF HARD AND SOFT TYPE PIEZOCERAMICS WITH TEMPERATURE FROM 2 TO 600 K

Authors: Miclea, C; Tanasoiu, T; Miclea, CF; Amarande, L; Cioangher, M; Trupina, L; Iuga, A; Spanulescu, I; Miclea, CT; David, C; Susu, M

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 304, DOI:

The application area of piezoceramic materials and devices based on such materials is continuously extended. The working conditions for such devices and structures may be sometimes very hard such as low and high temperatures, nuclear radiation, high pressure and so on. Such conditions may affect to some extent the transducer performances due to the changes of the basic properties of piezoceramic materials used as sensors. In this regard we have investigated the changes of the main piezoelectric properties of two typically hard and soft piezoceramics within a large temperature range from 2 to 600 K. All parameters measured showed a rather steady increase or decrease with increasing temperature. The results were discussed in terms of intrinsic and domain wall contribution to the dielectric and piezoelectric response of materials.

3050. Polymer-microporous host interactions probed by photoluminescence spectroscopy

Authors: Tiseanu, C; Parvulescu, VI; Cojocaru, B; Lorenz-Fonfria, VA; Kumke, M; Gessner, A; Enculescu, I

Published: 2010, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 3037, DOI: 10.1039/b922591a

Zeolites NaY and ZSM-5 were used as hosts for styrene polymerization after ion-exchange with europium ions. The parent and hybrid, polystyrene coated Eu-NaY (Eu-NaY/PS) and Eu-ZSM-5 (Eu-ZSM-5/PS) zeolites were investigated by using thermal analysis, SEM, PXRD, FT-IR, DR-UV/Vis, steady state and time-resolved photoluminescence spectroscopy. FT-IR spectra evidenced for the interaction between the zeolitic hosts and polystyrene while the PXRD spectra supported for the presence of the polymer inside the channels/pores of Eu-NaY/PS and Eu-ZSM-5/PS materials. The optical properties of Eu-NaY/PS and Eu-ZSM-5/PS were significantly changed relative to those of the parent zeolites, giving further evidence for the presence of polymer inside zeolites. An interesting case is presented by NaY zeolite: following styrene polymerization, the polymer interacted selectively with one of the two main species co-existing inside zeolite while for ZSM-5 a similar effect was not observed.