National Institute Of Materials Physics - Romania

Publications

5714 articles found

2711. Heteronuclear (Co-Ca, Co-Ba) 2,3-pyridinedicarboxylate complexes: synthesis, structure and physico-chemical properties

Authors: Lazarescu, A; Shova, S; Bartolome, J; Alonso, P; Arauzo, A; Balu, AM; Simonov, YA; Gdaniec, M; Turta, C; Filoti, G; Luque, R

Published: 2011, DALTON TRANSACTIONS, 40, 471, DOI: 10.1039/c0dt00858c

Three pyridine 2,3-dicarboxylate complexes have been synthesized and characterized by IR spectroscopy, thermal analysis and single crystal X-ray diffractometry. Their magnetic properties have also been studied by EPR and magnetisation measurements. The decomposition of such complexes in air leads to the generation of mixed metal oxides, as confirmed by powder X-ray diffraction.

2712. One-dimensional composites based on single walled carbon nanotubes and poly(o-phenylenediamine)

Authors: Baibarac, M; Baltog, I; Scocioreanu, M; Ballesteros, B; Mevellec, JY; Lefrant, S

Published: NOV-DEC 2011, SYNTHETIC METALS, 161, 2354, DOI: 10.1016/j.synthmet.2011.09.001

The direct mixing of aqueous ferric chloride and o-phenylenediamine (OPD) solution at room temperature in the absence and presence of carbon nanotubes (CNTs) has been used to prepare poly(o-phenylenediamine) (POPD) micro-fibers and composites of the type CNTs/POPD having nanotubes incorporated in polymer fiber mass. Using surface enhanced infrared absorption (SEIRA) spectroscopy significant modifications in the low frequency range of the polymer spectrum are revealed when Au is used as metallic support. Similar variations are reported for the POPD samples prepared by the electropolymerization of OPD onto rough Au electrode. A covalent functionalization of CNTs with POPD and a doping process of POPD with radical anions of CNTs is proved by surface enhanced resonant Raman scattering and SEIRA spectroscopy. The X-ray diffraction (XRD) studies indicate a high crystallinity both for POPD and CNTs/POPD composites prepared by chemical or electrochemical methods. (C) 2011 Elsevier B.V. All rights reserved.

2713. Successful Cleaning and Study of Contamination of Si(001) in Ultrahigh Vacuum

Authors: Gheorghe, NG; Lungu, GA; Husanu, MA; Costescu, RM

Published: 2011, PHYSICS CONFERENCE (TIM-10), 1387, DOI: 10.1063/1.3647078

This paper presents the very first surface physics experiment performed in ultrahigh vacuum (UHV) in Romania, using a new molecular beam epitaxy (MBE) installation. Cleaning of a Si(001) wafer was achieved by using a very simple technique: sequences of annealing at 900-1000 degrees C in ultrahigh vacuum: low 10(-8) mbar, with a base pressure of 1.5 x 10(-10) mbar. The preparation procedure is quite reproducible and allows repeated cleaning of the Si(001) after contamination in ultrahigh vacuum. The Si(001) single crystal surface is characterized by low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), and Auger electron spectroscopy (AES). The latter technique is utilized in order to investigate the sample contamination by the residual gas in the UHV chamber, as determined by a residual gas analyzer (RGA). Unambiguous assignment of oxidized and unoxidized silicon is provided; also, an important feature is that the LVV Auger peak at 90-92 eV cannot be solely attributed to clean Si (i.e. Si surrounded only by Si), but also to silicon atoms bounded with carbon. Even with a sum of partial pressures of oxygen and carbon containing molecules in the range of 5 x 10(-10) mbar, the sample is contaminated very quickly, having a (1/e) lifetime of about 76 minutes.

2714. Fe/Si(001) Ferromagnetic Layers: Reactivity, Local Atomic Structure and Magnetism

Authors: Lungu, GA; Costescu, RM; Anu, MAH; Gheorghe, NG

Published: 2011, PHYSICS CONFERENCE (TIM-10), 1387, DOI: 10.1063/1.3647075

Ultrathin ferromagnetic Fe layers on Si(001) have recently been synthesized using the molecular beam epitaxy (MBE) technique, and their structural and magnetic properties, as well as their interface reactivity have been investigated. The study was undertaken as function of the amount of Fe deposited and of substrate temperature. The interface reactivity was characterized by Auger electron spectroscopy (AES). The surface structure was characterized by low-energy electron diffraction (LEED). The magnetism was investigated by magneto-optical Kerr effect (MOKE). A higher deposition temperature stabilizes a better surface ordering, but it also enhances Fe and Si interdiffusion and it therefore decreases the magnetism. Despite the rapid disappearance of the long range order with Fe deposition at room temperature, the material exhibits a significant uniaxial in-plane magnetic anisotropy. For the Fe deposition performed at high temperature (500 degrees C), a weak ferromagnetism is still observed, with saturation magnetization of about 10 % of the value obtained previously. MOKE studies allowed inferring the main properties of the distinct formed layers.

2715. Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method

Authors: Tiseanu, C; Parvulescu, VI; Boutonnet, M; Cojocaru, B; Primus, PA; Teodorescu, CM; Solans, C; Dominguez, MS

Published: 2011, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 17145, DOI: 10.1039/c1cp21135h

Pure and europium (Eu3+) doped cerium dioxide (CeO2) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce4+ sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce4+ relative to Ce3+ ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.

2716. Nanocarbon embedded chalcogenides. Onion-like model

Authors: Popescu, M; Sava, F; Lorinczi, A; Velea, A; Simandan, ID

Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1453, DOI:

We modeled the equilibrium structure, at 0 K temperature, of some spherical As(2)S(3) molecules with only 12 rings of ten member (alternating As and S atoms) and 20 triangular faces: As(60)S(90) (like C(60)), As(140)S(210) (like C(140)), As(320)S(480) (like C(320)), grown on carbon fullerene and As(20)S(30) (like C(20)). We used a Monte-Carlo relaxation procedure in the frame of valence force fields theory. The onion-like configurations of the arsenic sulphide was demonstrated as possible. The deposited films of As(2)S(3) seen in the cross-section prove the presence of onion-like configurations even in pure As(2)S(3) material.

2717. Silver doped As2S3 chalcogenide films: A diffusion study

Authors: Lorinczi, A; Popescu, M; Sava, F; Velea, A; Simandan, ID

Published: 2011, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 9, 8, 2620, DOI: 10.1002/pssc.201084096

Photo-diffusion of silver across an As2S3 thin film layer is studied, as continuing some earlier work about surface morphology modifications in double-layer structures of Ag and As2S3, and some qualitative preliminary results on lateral Ag diffusion in As2S3 thin films. An estimation of the Ag film's dissolution rate and the diffusion front's advancement rate in As,S3 is given based on crosssection measurements. In order to understand better the diffusion mechanism of Ag in As2S3, a structural model of the As2S3 matrix is used to estimate the amount of silver which might be hosted by an As2S3 layer in terms of molar ratio, and an interaction mechanism of the Ag with the chalcogenide matrix is proposed. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2718. Modelling of Calcium Carbonate Synthesis by Gas-Liquid Reaction Using CO2 from Flue Gases

Authors: Isopescu, R; Mihai, M; Capat, C; Olaru, A; Mateescu, C; Dumitrescu, O; Udrea, I

Published: 2011, PRES 2011: 14TH INTERNATIONAL CONFERENCE ON PROCESS INTEGRATION, MODELLING AND OPTIMISATION FOR ENERGY SAVING AND POLLUTION REDUCTION, PTS 1 AND 2, 25, +, DOI: 10.3303/CET1125119

Green house gases, carbon dioxide, ozone, nitrous oxide and chlorofluorocarbons, result inevitably from fossil fuels combustion. The capture of CO2 from flue gases is an effective way to prevent the threat of global warming. The usage of flue gases with low CO2 content in the synthesis of precipitated calcium carbonate, a valuable mineral compound, seems to be an interesting solution for CO2 permanent removal. The quality of the solid product obtained (pure polymorphic phase and narrow particle size distribution in micron and sub-micron domain), can increase the value of the process due to the various applications of calcium carbonate (as filler in paper industry, pharmaceuticals, plastic materials and rubber). The present paper analyzes the chemical absorption of CO2 from flue gases in a waste lime solution. The important advantage of this process over conventional technologies of CO2 removal is that it provides a mineral product with many industrial uses, the fine crystallized CaCO3. Based on experimental results a mathematical model including the chemical process and the precipitation of solid phase was developed. The CO2 absorption was modeled using the general model for mass transfer with chemical reaction. The crystallization steps were modeled in the frame of population balance equation. The kinetic parameters corresponding to the crystallization process including nucleation, particle growth and agglomeration were estimated by nonlinear regression using experimental particle size distribution data.

2719. Electrochemical Growth of Eosin Y/Manganese Doped ZnO as Hybrid Films and Nanowires

Authors: Sima, M; Visan, T; Matei, E; Ungureanu, F; Enculescu, I; Sima, M

Published: 2011, ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS, 225, 339, DOI: 10.1524/zpch.2011.0042

The electrodeposition process of Eosin Y/ZnO:Mn as films and nanowires performed using a solution containing zinc and manganese nitrates + lactic acid mixture was studied by linear voltammetry. The films and wires grown by polarization at -1.1 V/SCE electrode potential were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, the Eosin Y presence was evidenced by optical measurements as absorption and photoluminescence spectroscopy. The manganese content in films depends on the nature of support electrode used. On the other hand, the presence of Eosin Y species in the deposition bath increased significantly the manganese concentration in the ZnO:Mn nanowires electrodeposited at -1.1 V/SCE.

2720. TRAPPING ASPECTS IN SILICON-BASED NANOSTRUCTURES

Authors: Ciurea, ML

Published: OCT-DEC 2011, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 12, 323, DOI:

Trapping aspects in two typical silicon-based nanostructures are investigated. Both 1D nanocrystalline porous silicon structures and 2D (nc-Si/CaF2)50 multilayered structures are considered. The curves of relaxation current versus temperature were obtained using the thermally stimulated currents method without external bias. Two types of maxima (rather broad maxima and spikes) were experimentally evidenced. The spikes are due to the stress-induced traps and their parameters are temperature dependent. To describe the trapping-detrapping-retrapping processes, a general model was proposed. The temperature dependence of stress-induced trap concentrations was described by a power law and the corresponding temperature dependence of cross-sections by a Gaussian law. The model was successfully applied on available experimental data.