National Institute Of Materials Physics - Romania

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5714 articles found

2801. XPS study of chemically sulphur-passivated n-GaAs

Authors: Ghita, RV; Negrila, CC; Ungureanu, F; Logofatu, C

Published: NOV 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1739, DOI:

A genuine GaAs surface was covered with a relatively thick layer (similar to nm) of native oxide pinning the surface Fermi level within the band gap of semiconductor. The method presented in this work is related to the sulphur passivation by treating n-GaAs in sulphide solutions (e.g. pure ammonium sulphide and sulphur monochloride) that combines both chemical and electronic passivation by reducing the surface state density. The presence of the covalent bonds As-S and Ga-S was putted into evidence by XPS analysis. It is presented the independence of XPS measurements on n-GaAs substrate orientation for (100) and (110) planes. At the surface of n-GaAs it is developed an adherent layer of sulphur compound as a result of chemical interaction of sulphur ions with n-GaAs surface.

2802. Molecular Relaxation Processes in a MOF-5 Structure Revealed by Broadband Dielectric Spectroscopy: Signature of Phenylene Ring Fluctuations

Authors: Frunza, S; Schonhals, A; Frunza, L; Ganea, P; Kosslick, H; Harloff, J; Schulz, A

Published: OCT 14 2010, JOURNAL OF PHYSICAL CHEMISTRY B, 114, 12846, DOI: 10.1021/jp1071617

The molecular mobility of a MOF-5 metal-organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed, The temperature dependence of their relaxation rates follows an Arrhenius law. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn-O clusters. The processes ("region II") at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. (I Am. Chem. Soc. 2008, 130, 3246). The carboxylate groups might also be involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region 11 corresponds nearly to a Debye-like process: This is explained by a well-defined structure or empty pores,

2803. Artificial pinning in thick YBCO films: Pinning potential and c-axis correlation

Authors: Crisan, A; Mikheenko, P; Sarkar, A; Dang, VS; Kechik, MMA; Abell, JS; Paturi, P; Huhtinen, H

Published: OCT 1 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, 843, DOI: 10.1016/j.physc.2010.02.033

We have introduced artificial pinning centres in thick (>1 mu m) YBCO films grown by Pulsed Laser Deposition using substrate decoration, quasi-multilayers, and target doping approaches. We have found that the frequency dependence of critical current density is consistent with a logarithmic dependence of pinning potential on current density. For most of materials used as nano-dots, artificially-induced pinning centres have a larger potential than natural ones. From angle-dependent in-field transport measurements and from Transmission Electron Microscopy we have found evidence of c-axis correlated pinning centres. (C) 2010 Elsevier B.V. All rights reserved.

2804. SiO2 nanospheres and tubes obtained by sol-gel method

Authors: Anastasescu, C; Anastasescu, M; Teodorescu, VS; Gartner, M; Zaharescu, M

Published: OCT 1 2010, JOURNAL OF NON-CRYSTALLINE SOLIDS, 356, 2640, DOI: 10.1016/j.jnoncrysol.2010.03.038

Multifunctional nanomaterials with one-dimensional structure have become very attractive because of their potential applications in biochemistry (bioseparation and biointeraction), drug delivery, catalysis, nanotechnology (optical sensors). In this work we report on the synthesis of SiO2 nanospheres and tubes, in a solution of tartaric acid (TTA), pure water and absolute ethanol, starting with tetraethyl orthosilicate (TEOS) via the addition of ammonium hydroxide. In order to characterize the obtained material, transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), thermogravimetric and thermodifferential analysis (DTA/TGA), FT-IR spectroscopy and spectroellipsometry (SE) were used. The tubes have an outer diameter of 0.1-0.2 mu m and length of some microns containing also spherical nanoparticles. The dimensions of the obtained nanotubes are tunable, their diameter and length depending on the synthesis conditions. In the presence of meso-tartaric acid no hollow tubes but nanospheres are obtained. The SiO2 tubes and nanospheres have similar structure but very different morphologies. The large surface area and the distinctive inner and outer surfaces represent a great advantage of the nanotubes over conventional nanoparticles, making these materials suitable for doping and differential functionalization. (C) 2010 Elsevier B.V. All rights reserved.

2805. Investigations of the neodymium doped quartz glasses obtained by the hybrid sot-gel method

Authors: Niciu, H; Vasiliu, C; Manea, A; Radu, D; Secu, M; Onose, C; Ghervase, L; Niciu, D; Feraru, ID; Grigorescu, CEA

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1623, DOI:

Undoped and neodymium doped quartz glasses were obtained by the hybrid sol-gel method. The vitrification was performed in He atmosphere. The Nd(3+) characteristic absorption bands in the UV and VIS were put into evidence. Investigations in the NIR range revealed a small amount (86 ppm) of OH(-) in the vitreous matrix. FTIR and Raman spectra exhibit the SiO(2) glass characteristic vibrations and also the characteristic vibrations of Si-OH and Si-Cl bonds. The photoluminescence peaks at 640, 920 and 1080 nm belonging to the Nd(3+) doped quartz glass were evidenced.

2806. Biocompatibility Studies of Iron-oxide-dextrin Thin Films

Authors: Andronescu, E; Costache, M; Ciobanu, CS; Prodan, AM; Predoi, D

Published: OCT 2010, REVISTA DE CHIMIE, 61, 928, DOI:

Dextrin coated magnetic nanoparticles have been obtained by co-precipitation. As a second step biocompatible magnetic thin film has been synthesized from the iron oxide coated with dextrin powders by pulsed laser deposition technique. Biocompatibility tests consisting of osteoblast cells growth, viability and proliferation were monitored on the surface of the thin films. The cells morphology was characterized by scanning electron microscopy (SEM) after 48h.

2807. Structural studies on serum albumins under green light irradiation

Authors: Comorosan, S; Polosan, S; Popescu, I; Ionescu, E; Mitrica, R; Cristache, L; State, AE

Published: OCT 2010, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, 39, 1491, DOI: 10.1007/s00249-010-0606-y

This paper presents two new experimental results: the protective effect of green light (GL) on ultraviolet (UV) denaturation of proteins, and the effect of GL on protein macromolecular structures. The protective effect of GL was revealed on two serum albumins, bovine (BSA) and human (HSA), and recorded by electrophoresis, absorption, and circular dichroism spectra. The effect of GL irradiation on protein structure was recorded by using fluorescence spectroscopy and electrophoresis. These new effects were modeled by quantum-chemistry computation using Gaussian 03W, leading to good fit between theoretical and experimental absorption and circular dichroism spectra. A mechanism for these phenomena is suggested, based on a double-photon absorption process. This nonlinear effect may lead to generation of long-lived Rydberg macromolecular systems, capable of long-range interactions. These newly suggested systems, with macroscopic quantum coherence behaviors, may block the UV denaturation processes.

2808. Looking for new synthesis of hydroxyapatite doped with europium

Authors: Ciobanu, CS; Andronescu, E; Vasile, BS; Valsangiacom, CM; Ghita, RV; Predoi, D

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1519, DOI:

In this work, we synthesized the properties of bioactive nanocrystalline hydroxyapatite (HAp), Ca-10(PO4)(6)(OH)(2) ceramic powder and nanocrystalline HAp doped with europium (III). The europium doped hydroxyapatite with an atomic ratio Eu/(Eu +Ca) between 2% and 20% were synthesized. The structure, morphology and optical properties were characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The XRD results reveal that the obtained Eu: HAp shows the characteristic peaks of hydroxyapatite in a hexagonal lattice structure. The results indicated that Eu3+ has been successfully doped into the framework of HAp.

2809. Vibrational and molecular dynamics of a nanoconfined liquid crystal

Authors: Schonhals, A; Frunza, S; Frunza, L; Unruh, T; Frick, B; Zorn, R

Published: OCT 2010, EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS, 189, 255, DOI: 10.1140/epjst/e2010-01329-5

The effect of a nanometer confinement on the vibrational and molecular dynamics of a liquid crystals E7 was studied by dielectric spectroscopy (DS) and neutron scattering (NS). E7 undergoes a glass transition phenomenon besides the nematic to isotropic phase transition. As confining host a molecular sieve of the MCM-41 type is used having cylindrical pores with a radius of 1.25 nm. The results obtained by both methods are compared in detail.

2810. Biomineralization capability of adherent bio-glass films prepared by magnetron sputtering (vol 21, pg 1047, 2010)

Authors: Stan, GE; Pina, S; Tulyaganov, DU; Ferreira, JMF; Pasuk, I; Morosanu, CO

Published: OCT 2010, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 21, 2899, DOI: 10.1007/s10856-010-4040-6