National Institute Of Materials Physics - Romania

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860 articles found

581. Synthesis, Structure, and Luminescent Properties of Europium-Doped Hydroxyapatite Nanocrystalline Powders

Authors: Ciobanu, CS; Iconaru, SL; Massuyeau, F; Constantin, LV; Costescu, A; Predoi, D

Published: 2012, JOURNAL OF NANOMATERIALS, 2012, DOI: 10.1155/2012/942801

The luminescent europium-doped hydroxyapatite (Eu:HAp, Ca10-xEux(PO4)(6)(OH)(2)) with 0 <= x <= 0.2 nanocrystalline powders was synthesized by coprecipitation. The structural, morphological, and textural properties were well characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The vibrational studies were performed by Fourier transform infrared, Raman, and photoluminescence spectroscopies. The X-ray diffraction analysis revealed that hydroxyapatite is the unique crystalline constituent of all the samples, indicating that Eu has been successfully inserted into the HAp lattice. Eu doping inhibits IIAp crystallization, leading to a decrease of the average crystallite size from around 20 nm in the undoped sample to around 7 nm in the sample with the highest Eu concentration. Furthermore, the samples show the characteristic D-5(0) -> F-7(0) transition observed at 578 nm related to Eu3+ ions distributed on Ca2+ sites of the apatitic structure.

582. Study of thiols deposition on GaAs

Authors: Ghita, RV; Cotirlan, C; Ungureanu, F; Florica, C; Negrila, CC

Published: JAN-FEB 2012, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 6, 244, DOI:

A genuine GaAs surface is 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 sulfur passivation by treating n-GaAs in different solutions of alkane thiols. At the surface of GaAs it is developed an adherent layer of sulfur compound as a result of chemical interaction of sulfur ions with GaAs(100) face, that are putted in evidence by scanning electron microscopy (SEM) images and second harmonic generation (SHG) analysis. Using X-ray photoelectron spectroscopy (XPS) is presented a detailed analysis of XPS data at the surface of thiols on GaAs together with the presence of the covalent bond As-S. The electric characteristics of the AuGeNi/Thiol/GaAs structure are presented in I (V) curves recorded in the region of small currents.

583. EUROPIUM DOPED HYDROXYAPATITE FOR APPLICATIONS IN ENVIRONMENTAL FIELD

Authors: Constantin, LV; Iconaru, S; Ciobanu, CS

Published: 2012, ROMANIAN REPORTS IN PHYSICS, 64, 794, DOI:

Due to the extensive use of new technologies in agricultural and industrial field the soil and groundwater were severely polluted with elements that may pose a serious threat to the environment. For that purpose studies concerning new materials that can be successfully used for removal of heavy metals and other toxic elements from contaminated soil and water were conducted. The attention of the scientific studies were focused on the family of calcium phosphates, with a particular interest in hydroxyapatite (HAp), with general formula Ca-10(PO4)(6)(OH)(2), due to the exquisite ability of adsorbing heavy element ions in aqueous conditions. This study focuses on synthesizing nanocrystalline hydroxyapatite powders with controllable parameters and very good stoechiometry. The structure, morphology and optical properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR).

584. Fano-Kondo oscillations of the conductance and thermopower in a mesoscopic transistor

Authors: Aldea, A; Tolea, M; Dinu, IV

Published: 2012, 14TH INTERNATIONAL CONFERENCE ON TRANSPORT IN INTERACTING DISORDERED SYSTEMS (TIDS-14), 376, DOI: 10.1088/1742-6596/376/1/012019

We study the conductance G and Seebeck coefficient S of a side-coupled double quantum dot system. The transport properties are the result of the competition between the Fano interference and Kondo correlations, being also controlled by the Coulomb blockade of the multilevel side-dot. The external parameters are the gate potential V-g applied on the side-dot and the temperature. When V-g is varied continuously the blockade is switched on and off periodically, resulting in oscillations of the transport coefficients. The profile of the oscillations and the temperature dependence are studied. An extended Anderson model and the Keldysh transport formalism are used.

585. Zero bias anomalies in the Kondo regime of single and double quantum dots

Authors: Aldea, A; Tolea, M; Dinu, IV

Published: 2012, ADVANCED MANY-BODY AND STATISTICAL METHODS IN MESOSCOPIC SYSTEMS, 338, DOI: 10.1088/1742-6596/338/1/012001

The zero bias anomaly of the differential conductance of mesoscopic systems is a fingerprint of the electron-electron interaction. The common example is the peak of the differential conductance in Kondo mesoscopic systems. We show that in complex mesoscopic systems, in particular in the side-coupled double dot, the dip of the differential conductance at zero bias is also possible due to simultaneous effects of interference and correlations. The external parameters that control this effect are the temperature and the gate potential on the lateral dot. We argue that even in single dots, in a multiple lead configuration, the shift from suppression to enhancement of dI/dV with increasing bias is allowed if the bias applied on the leads is not symmetric. The differential conductance exhibits a peak-dip crossover, the effect being controlled by the strength of the asymmetry and the ratio of the dot-lead couplings. The scaling of the differential conductance for the double-dot system is also discussed. The results are obtained using an extended Anderson model, the Keldysh transport formalism and the equation of motion technique extended to the non-equilibrium.

586. Structural and physical properties of antibacterial Ag-doped nano-hydroxyapatite synthesized at 100A degrees C

Authors: Ciobanu, CS; Massuyeau, F; Constantin, LV; Predoi, D

Published: DEC 3 2011, NANOSCALE RESEARCH LETTERS, 6, 8, DOI: 10.1186/1556-276X-6-613

Synthesis of nanosized particle of Ag-doped hydroxyapatite with antibacterial properties is in the great interest in the development of new biomedical applications. In this article, we propose a method for synthesized the Ag-doped nanocrystalline hydroxyapatite. A silver-doped nanocrystalline hydroxyapatite was synthesized at 100A degrees C in deionized water. Other phase or impurities were not observed. Silver-doped hydroxyapatite nanoparticles (Ag:HAp) were performed by setting the atomic ratio of Ag/[Ag + Ca] at 20% and [Ca + Ag]/P as 1.67. The X-ray diffraction studies demonstrate that powders made by co-precipitation at 100A degrees C exhibit the apatite characteristics with good crystal structure and no new phase or impurity is found. The scanning electron microscopy (SEM) observations suggest that these materials present a little different morphology, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O), and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) analysis. FT-IR and FT-Raman spectroscopies revealed that the presence of the various vibrational modes corresponds to phosphates and hydroxyl groups. The strain of Staphylococcus aureus was used to evaluate the antibacterial activity of the Ca10-x Ag (x) (PO4)6(OH)2 (x = 0 and 0.2). In vitro bacterial adhesion study indicated a significant difference between HAp (x = 0) and Ag:HAp (x = 0.2). The Ag:Hap nanopowder showed higher inhibition.

587. Effect of maleic anhydride-aniline derivative buffer layer on the properties of flexible substrate heterostructures: Indium tin oxide/nucleic acid base/metal

Authors: Stanculescu, A; Socol, M; Socol, G; Mihailescu, IN; Girtan, M; Preda, N; Albu, AM; Stanculescu, F

Published: DEC 1 2011, THIN SOLID FILMS, 520, 1258, DOI: 10.1016/j.tsf.2011.04.204

This paper presents some investigations on the properties of guanine (G) and cytosine (C) based heterostructures deposited on flexible substrates. The effects of two types of maleic anhydride-aniline derivatives (maleic anhydride-cyano aniline or maleic anhydride-2,4 dinitroaniline) buffer layer, deposited between indium tin oxide and (G) or (C) layer, on the optical and electrical properties of the heterostructures have been identified. The heterostructures containing a film of maleic anhydride-2,4 dinitroaniline have shown a good transparency and low photoluminescence invisible range. This buffer layer has determined an increase in the conductance only in the heterostructures based on (G) and (C) deposited on biaxially-oriented polyethylene terephthalate substrate. (C) 2011 Elsevier B. V. All rights reserved.

588. Highly adherent bioactive glass thin films synthetized by magnetron sputtering at low temperature

Authors: Stan, GE; Pasuk, I; Husanu, MA; Enculescu, I; Pina, S; Lemos, AF; Tulyaganov, DU; El Mabrouk, K; Ferreira, JMF

Published: DEC 2011, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 22, 2710, DOI: 10.1007/s10856-011-4441-1

Thin (380-510 nm) films of a low silica content bioglass with MgO, B2O3, and CaF2 as additives were deposited at low-temperature (150A degrees C) by radio-frequency magnetron sputtering onto titanium substrates. The influence of sputtering conditions on morphology, structure, composition, bonding strength and in vitro bioactivity of sputtered bioglass films was investigated. Excellent pull-out adherence (similar to 73 MPa) was obtained when using a 0.3 Pa argon sputtering pressure (BG-a). The adherence declined (similar to 46 MPa) upon increasing the working pressure to 0.4 Pa (BG-b) or when using a reactive gas mixture (similar to 50 MPa). The SBF tests clearly demonstrated strong biomineralization features for all bioglass sputtered films. The biomineralization rate increased from BG-a to BG-b, and yet more for BG-c. A well-crystallized calcium hydrogen phosphate-like phase was observed after 3 and 15 days of immersion in SBF in all bioglass layers, which transformed monotonously into hydroxyapatite under prolonged SBF immersion. Alkali and alkali-earth salts (NaCl, KCl and CaCO3) were also found at the surface of samples soaked in SBF for 30 days. The study indicated that features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings.

589. Electrodeposited ZnO films with high UV emission properties

Authors: Matei, E; Enculescu, I

Published: NOV 2011, MATERIALS RESEARCH BULLETIN, 46, 2154, DOI: 10.1016/j.materresbull.2011.04.025

We report here our results in the preparation of ZnO films with high UV band to band characteristic luminescence emission by potentiostatic electrodeposition. Zinc nitrate aqueous baths with different concentration and additives were employed for the preparation of the films on platinum substrates. We focused our research in determining how the electrodeposition bath composition, i.e. zinc nitrate concentration and addition of KCI or polyvinyl pyrolidone and applied overpotential influence the morphological and optical properties of the oxide films. Scanning electron microscopy was employed for characterizing the films in terms of morphology. Optical reflection, photoluminescence spectroscopy and cathodoluminescence were used for determining the optical characteristics of the samples. The morphology of the deposit varies from hexagonal prisms to platelets as a function of the deposition rate. This experimental parameter also influences the luminescence properties. We found that at low deposition rates high UV luminescent material is obtained. (C) 2011 Elsevier Ltd. All rights reserved.

590. Upconversion luminescence of Er, Yb - doped nanolanganite powders synthesized by a citrate sol-gel method

Authors: Voiculescu, AM; Georgescu, S; Toma, O; Nastase, S; Birjega, R; Petrescu, L; Enculescu, I; Matei, E

Published: NOV 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 1173, DOI:

Langanite nanopowders doped with erbium and ytterbium were prepared by a citrate sol-gel method and annealed in air at various temperatures between 700 degrees C and 1000 degrees C. For annealing temperatures 900 degrees C and 1000 degrees C, part of the langanite transforms in perovskite (LaGaO(3)), as evidenced in XRD spectra. The reddish color of the powders due to color centers associated to oxygen defects intensifies with increasing annealing temperature. Green and red luminescence was obtained for IR (933 nm) pumping and only green for UV pump. The mechanisms involved in luminescence and energy transfer processes are presented and discussed.