National Institute Of Materials Physics - Romania

Publications

5781 articles found

2861. MAPLE preparation and characterization of benzil thin films

Authors: Socol, M; Socol, G; Rasoga, O; Stanculescu, F; Stanculescu, A; Mihailescu, I; Ionita, I; Preda, N; Enculescu, M; Antohe, S

Published: NOV 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1806, DOI:

In this study the Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique was used to prepare thin films from a low melting point (< 100 degrees C) organic compound (benzil). Optical properties of the films have been investigated by UV-VIS, FTIR and PL spectroscopy. Details about crystallinity were obtained by XRD measurements. FTIR spectra have confirmed the preservation of the chemical structure of the compound during the deposition process. SEM and AFM investigation have evidenced a topography of the MAPLE deposited films characterized by different grain size depending on the deposition conditions. Second harmonic generation measurements have revealed that the MAPLE deposited benzil films have preserved the optical nonliniar properties of the bulk crystalline benzil.

2862. STRUCTURAL DETAILS OF THE Ag-As2S3 INTERFACE OBTAINED BY VACUUM THERMAL EVAPORATION FOLLOWED BY GREEN LASER IRRADIATION

Authors: Lorinczi, A; Velea, A; Matei, E; Simandan, ID; Popescu, M

Published: NOV 2010, CHALCOGENIDE LETTERS, 7, 612, DOI:

As2S3 on Ag heterostructures deposited onto microscope glass substrates have been prepared. The quality of the hetero-structures has been investigated by careful analysis of the scanning electron microscope pictures taken on the native cross-sections, produced after the vacuum deposition sequence and various green laser irradiation times. The As2S3 layer is not uniformly grown, but reveals a columnar-like structure and multi-scale aggregation.

2863. The effects of organic additives on induction time and characteristics of precipitated calcium carbonate

Authors: Isopescu, R; Mateescu, C; Mihai, M; Dabija, G

Published: NOV 2010, CHEMICAL ENGINEERING RESEARCH & DESIGN, 88, 1454, DOI: 10.1016/j.cherd.2009.10.002

The effects of an organic additive, polyoxyethylene sorbitan trioleate (Tween 85), on the induction time for the precipitation of calcium carbonate are experimentally and theoretically investigated. Calcium carbonate was precipitated from aqueous solutions of K2CO3 and Ca(NO)(3) at moderate supersaturations ranging between 5 and 16 with and without the organic additive. Experimentally it has been noticed that the induction period for CaCO3 precipitation increases at low supersaturation and is also influenced by temperature. An increase of the induction time was noticed when Tween 85 was added in the system. The "cluster coagulation model" proposed by Qian and Botsaris (1997), which combines nucleation models and coagulation theory, was used to explain the effects of operating parameters on the induction time in terms of interfacial energy and cluster sizes. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

2864. Synthesis and characterization of xTiO(2 center dot)(1-x)alpha-Fe2O3 magnetic ceramic nanostructure system

Authors: Sorescu, M; Xu, TH; Diamandescu, L

Published: NOV 2010, MATERIALS CHARACTERIZATION, 61, 1118, DOI: 10.1016/j.matchar.2010.07.004

Rutile doped hematite xTiO(2) (1-x)alpha Fe2O3 (x=0 0-10) nanostructures were synthesized using mechanochemical activation by ball milling Their complex structural magnetic and thermal properties were characterized by X ray diffraction Mossbauer spectroscopy and simultaneous DSC-TGA XRD patterns yielded the dependence of lattice parameters and grain size as a function of ball milling time For the molar concentrations x=0 1 and 03 the Mossbauer spectra were fitted with one two three or four sextets corresponding to the degree of Ti ion substitution of Fe ions in hematite lattice After 12 h of ball milling the completion of Ti ion substitution of Fe ions in hematite lattice occurs for x=0 1 and 03 For x=0 5 and 07 Mossbauer spectra fitting required sextets and a quadrupole split doublet representing Fe ions substituting Ti ions in the rutile lattice The completion of Fe ion substitution of Ti ions in rutile lattice was not observed as indicated by XRD patterns and Mossbauer spectra for these two molar concentrations Simultaneous DSC-TGA measurements revealed that the mechanochemical activation by ball milling has a strong effect on the thermal behavior of this nanostructure system The enthalpy dropped dramatically after 2 h of milling time indicating the strong solid-solid interactions between TiO2 and a Fe2O3 after ball milling The change in weight loss of hematite was caused by the decrease of grain size and ion substitutions between Fe and Ti after mechanochemical activation (C) 2010 Elsevier Inc All rights reserved

2865. Nano and micro-morphology modifications of Si (100) substrate induced by femtosecond laser pulse irradiations in air, water, CCl4 and C2Cl3F3

Authors: Ionel, L; Cristescu, CP; Jipa, F; Enculescu, M; Radoiu, M; Dabu, R; Zamfirescu, M; Ulmeanu, M

Published: NOV 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1924, DOI:

The aim of this study is to investigate the influence of the different media, e.g. air, water, CCl4 (carbon tetrachloride) and C2Cl3F3 (tricloro-trifluoro-ethane), when irradiating a Si (100) substrate, with a 200 femtosecond (fs) laser pulses of a Ti:sapphire laser operating at 775 nm. Various micro and nanomorphologies could be achieved by changing the media, the laser pulse energy and the number of pulses. It is shown that the resulting Si (100) surface presents a regulated morphology in air consisting of parallel ripples and the formation of regular arrays of submicrometer spikes on Si (100) in CCl4 and C2Cl2F3, respectively. Irradiation of a Si (100) substrate immersed in water creates a regularly structured surface but it doesn't facilitate the spikes formation. The potential use of the patterned Si substrates as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged.

2866. MOULDING PROCEDURE FOR THE PREPARATION OF INFRARED GLASSY MICROLENSES AND PRISMS BASED ON ARSENIC SULPHIDE CHALCOGENIDE GLASS

Authors: Niciu, H; Popescu, M; Velea, A; Lorinczi, A; Manea, A; Niciu, D; Lazarescu, M

Published: NOV 2010, CHALCOGENIDE LETTERS, 7, 629, DOI:

A new procedure for the production of infrared lenses and prisms based on As(2)S(3) chalcogeniude glass has been devised. Infrared components are obtained with the size in the range 100-1500 micrometers. The procedure allows for getting various curvature radii of the micrometer lenses, ranging from planno-convex to spherical ones.

2867. Cobalt-doped ZnO prepared by electrochemistry: Chemistry, morphology, and magnetism

Authors: Matei, E; Enculescu, I; Vasilache, V; Teodorescu, CM

Published: NOV 2010, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 207, 2522, DOI: 10.1002/pssa.200925378

ZnO:Co thin films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, optical spectroscopy, and cathodoluminescence, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). An increase of structural disorder and crystallite reorientation are observed for cobalt-doped samples. MOKE magnetometry revealed room-temperature ferromagnetic behavior only for ZnO: Co deposited at -850 mV. These are the samples with the lower cobalt content and lowest structural perturbation of the ZnO matrix by cobalt. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2868. 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.

2869. 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,

2870. 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.