National Institute Of Materials Physics - Romania

Publications

860 articles found

491. Polysaccharide-assisted crystallization of ZnO micro/nanostructures

Authors: Preda, N; Enculescu, M; Enculescu, I

Published: JAN 15 2014, MATERIALS LETTERS, 115, 260, DOI: 10.1016/j.matlet.2013.10.081

ZnO micro/nanostructures with complex morphology were synthesized by a simple chemical reaction between zinc nitrate and hexamethylenetetramine in the presence of polysaccharides. X-ray diffraction analysis showed that all obtained samples are of wurtzite structure. The reflectance and room temperature photoluminescence spectra have been used to investigate the optical properties of the ZnO structures. The scanning electron microscopy images reveal that the ZnO morphology (star, double-jellyfish, double-raspberry and edelweiss-flower) can be easily changed by varying the polysaccharides: sodium alginate, gum arabic and chitosan. The polysaccharide-assisted crystallization method could provide a facile approach to synthesize other desired compounds with controllable morphology. (C) 2013 Elsevier B.V. All rights reserved.

492. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays

Authors: Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L

Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062

A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

493. Dual emitter IrQ(ppy)(2) for OLED applications: Synthesis and spectroscopic analysis

Authors: Ciobotaru, IC; Polosan, S; Ciobotaru, CC

Published: JAN 2014, JOURNAL OF LUMINESCENCE, 145, 262, DOI: 10.1016/j.jlumin.2013.07.067

The synthesis of organometallic compound with iridium and two types of ligands, quinoline and phenylpyridine, was done successfully. The absorption spectra of this compound have shown broad peaks in a visible region assigned to metal-to-ligands charge transfer and in UV region assigned to intraligand absorptions. The photoluminescence spectra exhibit dual character in which the red emission is more intense than the green one. In cathodoluminescence measurements, under electron beam, the powder obtained after recrystallization from dichloromethane, shows similar behaviors with photoluminescence spectra. The cathodoluminescence images have shown a luminescent crystalline powder with triclinic structure. This compound exhibits combined vibrational modes, which proves the presence in the same molecule of both ligands. Density Functional Theory calculation was involved in order to identify the main vibrations of this compound. (C) 2013 Elsevier B.V. All rights reserved.

494. OPTICAL CHARACTERISTICS OF SULPHUR-PASSIVATED n-GaAs (100) SURFACE

Authors: Ghita, RV; Grigorescu, CEA; Secu, M; Predoi, D; Frumosu, F; Cotirlan, C; Feraru, ID

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1478, DOI:

A genuine GaAs surface is covered with a relatively thick layer (similar to 10 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(100) and (110) in sulphide solutions (e.g pure ammonium sulphide and sulphur monochloride) that combines both chemical electronic passivation by reducing the surface state density. The effects of passivation were put into evidence by Photoluminescence measurements where it was observed the variation of state density. The presence of sulphur dipoles at surface was presented in a diagram of Second Harmonic Generation analysis and the general aspect of sulphur compound was identified by SEM images. The presence of the covalent bond Ga-S and the variation of surface barrier as well as the effect of crystal orientation were put into evidence by micro-Raman Spectroscopy. At the surface of n-GaAs it is developed an adherent layer of sulphur compound as a resul of chemical interaction of sulphur ions with n-GaAs surface.

495. EFFECTS OF PROCESS PARAMETERS ON GROWTH OF METAL PARTICLES BY ATMOSPHERIC PRESSURE PLASMA JET

Authors: Lazea-Stoyanova, A; Enculescu, M; Vizireanu, S; Marascu, V; Dinescu, G

Published: JUL-SEP 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1247, DOI:

In this paper we report a procedure of growing metallic particles at atmospheric pressure by using a radiofrequency plasma jet, operated in inert gaseous atmosphere (argon). Iron metallic particles are manufactured, with sizes in the range of hundreds of nm up to a few microns, having as metal source the electrodes of the plasma jet discharge. The obtained particles are characterized with respect to their shape, size, morphology and size distribution. An emphasis is put on the relationship between the particle size distribution and process parameters, namely the substrate to nozzle distance and applied radiofrequency power.

496. Antimicrobial Activity of Thin Solid Films of Silver Doped Hydroxyapatite Prepared by Sol-Gel Method

Authors: Iconaru, SL; Chapon, P; Le Coustumer, P; Predoi, D

Published: 2014, SCIENTIFIC WORLD JOURNAL, DOI: 10.1155/2014/165351

In this work, the preparation and characterization of silver doped hydroxyapatite thin films were reported and their antimicrobial activity was characterized. Silver doped hydroxyapatite (Ag:HAp) thin films coatings substrate was prepared on commercially pure Si disks by sol-gel method. The silver doped hydroxyapatite thin films were characterized by various techniques such as Scanning electron microscopy (SEM) with energy Dispersive X-ray attachment (X-EDS), Fourier transform infrared spectroscopy (FTIR), and glow discharge optical emission spectroscopy (GDOES). These techniques have permitted the structural and chemical characterisation of the silver doped hydroxyapatite thin films. The antimicrobial effect of the Ag:HAp thin films on Escherichia coli and Staphylococcus aureus bacteria was then investigated. This is the first study on the antimicrobial effect of Ag:HAp thin films obtained by sol-gel method. The results of this study have shown that the Ag:HAp thin films with x(Ag) = 0.5 are effective against E. coli and S. aureus after 24 h.

497. Metallic Nanowires and Nanotubes Prepared by Template Replication

Authors: Matei, E; Enculescu, M; Preda, N; Florica, C; Costas, A; Busuioc, C; Molares, MET; Kuncser, V; Enculescu, I

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 165, DOI: 10.1007/978-3-662-44479-5_6

Low dimensional nanostructures represent a hot scientific field nowadays due mainly to the tremendous potential for applications. Low dimensions open the possibilities for both ultra-miniaturization and increase in functionality. Numerous procedures were developed for fabricating such nanostructures. Template replication represents a highly effective method in fabricating metallic nanowires and nanotubes. The approach is characterized by the excellent control in obtaining nano objects with the desired shape and dimensions. A large variety of templates are available ranging from viruses and proteins to nanoporous membranes fabricated by using swift heavy ion accelerators. In the following chapter the main steps involved in employing the method for fabricating metalic nanowires and nanotubes by replicating ion track nanoporous membranes were described. The steps include here membrane fabrication and replication and involve track etching and electrochemical metal deposition. The influence of the process parameters on the properties of the nanoobjects prepared by this approach was reviewed. It was found that simple experimental parameters can be chosen in such a way that the functionality of the nanowires or nanotubes can be finely tuned.

498. Hydroxyapatite With Environmental Applications

Authors: Popa, CL; Ciobanu, CS; Petre, CC; Motelica-Heino, M; Iconaru, SL; Jiga, G; Predoi, D

Published: 2014, TIMES OF POLYMERS (TOP) AND COMPOSITES 2014, 1599, 321, DOI: 10.1063/1.4876842

The aim of this study was to synthetize new nanoparticles based on methyltrimethoxysilane coated hydroxyapatite (MTHAp) for lead removal in aqueous solutions. The morphological and compositional analysis of MTHAp was investigated by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Removal experiments of Pb2+ ions were carried out in aqueous solutions with controlled concentration of Pb2+ and at fixed pH of 5. After the removal experiment of Pb2+ ions from solutions, porous hydroxyapatite nanoparticles were transformed into PbMTHAp_5 via the adsorption of Pb2+ ions followed by a cation exchange reaction. Our results demonstrate that the porous hydroxyapatite nanoparticles can be used as an adsorbent for removing Pb2+ ions from aqueous solution.

499. INFLUENCE OF PREPARATION STEPS ON THE PROPERTIES OF ELECTROSPUN ZnO FIBERS

Authors: Busuioc, C; Evanghelidis, A; Florica, C; Enculescu, I

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1578, DOI:

ZnO nanofibers were obtained by calcination of electrospun Zn(Ac)(2)center dot 2H(2)O/PMMA composite fibers and characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. The thermal treatment led to polymer burning and polycrystalline hexagonal ZnO phase formation. The average fiber diameters range between 450 and 600 nm before calcination and 200 - 300 nm after calcination. PL investigation revealed a strong dependence of ZnO fibers emission band on the calcination temperature. Furthermore, electrical contacts were fabricated by photolithography and electric characteristics were measured.

500. Electroluminescence of OLED based IrQ(ppy)(2)-5Cl organometallic compound: Theoretical considerations

Authors: Polosaw, S; Ciobotaru, IC

Published: JAN-FEB 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 92, DOI:

The electroluminescence and current density versus applied voltage were measured for the OLED cell structure which contain IrQ(ppy)(2)-5Cl as emitting layer. Two parameters, emission quantum yield and charge transport behaviors, which influences the electroluminescence, were modeled mainly concerning the non-radiative rate constants, delocalization of the HOMO and LUMO states, internal reorganization energies and bandgap of IrQ(ppy)(2)-5Cl. The non-radiative constant rates were determined using the three zero-field splitting substates responsible for the phosphorescence model and shows an increasing of these rates together with a strong interaction with the polystyrene matrix. Delocalization of the HOMO and LUMO states on the quinoline ligand, together with the small reorganization energies and bandgap lowering indicates good charge transport properties for the IrQ(ppy)(2)-5Cl compound.