National Institute Of Materials Physics - Romania

Publications

472 articles found

401. Optical and structural investigations on rare earth-doped thin films of phosphate glasses prepared by pulsed laser deposition

Authors: Vasiliu, C; Epurescu, G; Niciu, H; Dumitrescu, O; Negrila, C; Elisa, M; Filipescu, M; Dinescu, M; Grigorescu, CEA

Published: JAN 2009, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 20, 289, DOI: 10.1007/s10854-008-9583-7

Thin films of phosphate glasses were prepared by pulsed laser deposition in oxygen atmosphere on ITO-coated glass and silicon substrates respectively, using a Nd:YAG laser (266 nm). The targets were Li(2)O-Al(2)O(3)-P(2)O(5) bulk glasses doped with Pr and Nd. Infrared transmission-, energy dispersive X-ray- and X-ray photoemission spectroscopy investigations carried out on targets as well as on the deposited films proved a satisfactory compositions transfer on both substrates. Scanning electron microscopy and atomic force microscopy show continuous films with glassy spheres. Processes where substrates were positioned perpendicularly to targets produced discontinuous drops free films.

402. Synthesis, structural characterization, and photocatalytic properties of iron-doped TiO2 aerogels

Authors: Popa, M; Diamandescu, L; Vasiliu, F; Teodorescu, CM; Cosoveanu, V; Baia, M; Feder, M; Baia, L; Danciu, V

Published: JAN 2009, JOURNAL OF MATERIALS SCIENCE, 44, 364, DOI: 10.1007/s10853-008-3147-3

Fe(III)-doped TiO2 aerogels are prepared by acid catalyzed sol-gel method followed by supercritical drying, and then heat treatment. Raman spectra together with X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of the iron-doped TiO2 aerogel samples revealed the existence of both anatase and brookite crystalline phases. It was found that the brookite phase formation is favored by the increase of the iron content in the dried samples. XRD measurements show that the lattice constant c of anatase phase decreases with the dopant addition, while the value of a remains essentially unchanged. The microstructure of the investigated samples is relatively compact with small mesopores as revealed from transmission electron microscopy (TEM). The most enhanced photocatalytic activity was exhibited by the TiO2 aerogel sample with 1.8 at.% Fe(III) whose apparent rate constant of the salicylic acid photodegradation was found to be of almost six times higher than that of Degussa P25.

403. ASPECTS OF TEMPERATURE DEPENDENCE ON Au-Ti/GaAs(SI) SCHOTTKY BARRIER

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

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 458, DOI:

Fabrication of Au-Ti Schottky structure on GaAs semi-insulating wafer was related to an ultra-high vacuum deposition condition and low vacuum annealing in low vacuum and temperature range T=320-360 degrees C. There are presented representative I-V characteristics in dark and in different light (power levels). The spectral response has a maximum in Delta lambda = (850-950) nm corresponding to a band-to-band transition. The complex dependence of optical generated non-equilibrium carriers is related to the equivalent state density at the conduction band edge (in T(3/2) factor) and in exponential distribution factor exp (-(E-F)/kT).

404. Cobalt doped ZnO prepared by electrochemistry: chemistry, morphology, and magnetism

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

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 3, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: BIOFUELS, RENEWABLE ENERGY, COATINGS FLUIDICS AND COMPACT MODELING, +, DOI:

ZnO:Co thin Films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). Increse of structural disorder and crystallite re-orientation are observed for cobalt doped samples (especially for those obtained at - 750 and at - 800 mV overpotentials). MOKE magnetometry revealed room temperature ferromagnetic behaviour only for ZnO:Co deposited at - 850 mV. These are the samples with the less cobalt content and lowest structural perturbation of the ZnO matrix by cobalt.

405. ABSORPTION AND LUMINESCENCE PROPERTIES OF C-70 AGGREGATES IN SOLVENT MIXTURES

Authors: Husanu, AM; Baltog, I; Baibarac, M; Preda, N; Mihut, L; Velula, T; Bucur, C

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 538, DOI:

We report the formation of stable C-70 aggregate forms in o-dichlorobenzene/N-methyl-2-pyrrolidinone (DCB/NMP) and o-dichlorobenzene/acetonitrile (DCB/ACN) mixtures and their characterization by UV-VIS absorption spectroscopy and photoluminescence. As NMP acts on C-70 both as a solvent and reactant due to the unpaired electrons of the amidic nitrogen atom, molecular complexes (C-70/NMP) that aggregate slowly are formed by the binding of the NMP molecule to the fullerene cage. This interaction is seen in the UV-VIS absorption spectra of C-70 in DCB/NMP solvent mixtures by a gradual modification of the absorption spectra when increasing the NMP concentration. On the other hand, DCB and ACN combined form it typical solvent/non-solvent mixture favoring an intense aggregation of fullerenes. This yields to the C-70 clusters formations, having different size, similar to a precipitation process. Their characteristic is an abrupt variation in the absorbance appearing when the ACN is used in a greater extent. This different behavior of C-70 aggregation in DCB/NMP and DCB/ACN mixtures is also seen in their luminescence spectra recorded at different excitation wavelengths. While the PL spectra of C-70 solvated in DCB/NMP solution keeps almost the same modified shape irrespective the NMP concentration, the luminescence spectra Of C-70 in DCB/ACN mixture partially regains the powder C-70 PL signature as the ACN concentration is increased.

406. THE INTERCALATION OF PbI2 WITH 2,2 '-BIPYRIDINE EVIDENCED BY PHOTOLUMINESCENCE. FT-IR AND RAMAN SPECTROSCOPY

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I; Husanu, M; Bucur, C; Velula, T

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 675, DOI:

Hybrid material based on PbI2 intercalated with 2,2'-bypiridine (BIPY) was investigated by correlated studies of photoluminescence. infrared absorption and Raman spectroscopy. The PbI2(BIPY) intercalated compound has been synthesized by the chemical reaction of K1 and Pb(NO3)(2) in aqueous BIPY solution The optical studies reveal different properties for the hybrid material in comparison with those of pure PbI2 and BIPY. In the photoluminescence spectrum of the intercalated compound. recorded at liquid nitrogen temperature a new intense hand emission with maximum at 2 07 eV is observed. The excitation spectrum reveals it broad hand featured by several maxima at 2.77, 3.34 and 3 70 eV. New absorption bands at about 1589, 1489, 1435, 1312, 1009 cm(-1) are observed in the IR spectrum of PbI2(BIPY). The Raman spectrum of intercalated compound discloses new lines at 67, 83, 127 cm(-1) and the shift of two Raman lines from 994 cm(-1) to 1010 cm(-1) and from 1045 cm(-1) to 1060 cm(-1). A charge transfer process, leading to the formation of lead-BIPY coordination complexes. is considered its responsible for the strong host-guest interaction revealed by almost all experimental data

407. VIBRATIONAL PROPERTIES OF POLYANILINE FUNCTIONALIZED PbI2

Authors: Baltog, I; Baibarac, M; Mihut, L; Preda, N; Velula, T; Bucur, C; Husanu, M

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 688, DOI:

Functionalization of PbI2 with polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES) is demonstrated by Raman spectroscopy. Two functionalization methods were used: electrochemical polymerization of aniline onto the PbI2 modified Pt electrode and the mechanico-chemical reaction between PANI and PbI2. The functionalization induces changes in the Raman spectrum of PbI2 that consist in the appearance of new Raman lines with the peaks at 80, 144 and 170 cm(-1) The first line is the signature of the "stacking faults" that disrupt the stacking sequence of layers I-Pb-I atomic layers along the c crystalline axis by the intercalation of polymer molecules The bands at 144 and 170 cm(-1) are attributed to a vibrational mode associated to the Pb-NHR"(2) (R" = C6H4) bond.

408. Pulsed laser co-deposition of titania with Fe: chemistry, local atomic structure, and light-dependent magnetic properties

Authors: Negrila, C; Logofatu, C; Socol, G; Macovei, D; Teodorescu, CM

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:

TiO2:Fe thin films prepared by pulsed laser deposition exhibit in some case light dependent saturation magnetization, as determined from Kerr magnetometry measurements performed in dark or by illuminating the sample. This phenomenon is Studied in correlation with local atomic Structure investigated by extended X-ray absorption fine structure, composition and chemical state analyzed by X-ray photoelectron spectroscopy and by Xray absorption near-edge structure. It is found that light-controllable magnetism is a property of a mixture of Fe and oxidized Fe clusters embedded in the anatase TiO2 matrix.

409. Fabrication and characterization of nano-structured ferromagnetic Ti1-xFexO2 thin films

Authors: Apetrei, R; Negrila, C; Macovei, D; Dascaleanu, V; Teodorescu, CM; Mardare, D; Luca, D

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:

Nanostructured intrinsic and doped titania materials have long been subject to both basic and applied research, in connection with environment and energy related applications. Apart from beneficial effects. such as widening the wavelength range for surface photocatalytic activation, doping TiO2 materials with 3d ferromagnetic cations is a main route to develop ail important class of diluted semiconductors, with potential applications in spintronics. In all the previous investigations the concentration of the ferromagnetic dopant was limited to a few percents. Here, we initiate ail extended investigation of Ti1-xFexO2 within a, wider iron composition range (x = 0 - 0.55) and discuss the magnetic and optical properties of these materials in thin films in relation with their elemental composition, nano-structure and local atomic ordering.

410. Structural and photocatalytic properties of iron- and europium-doped TiO2 nanoparticles obtained under hydrothermal conditions

Authors: Diamandescu, L; Vasiliu, F; Tarabasanu-Mihaila, D; Feder, M; Vlaicu, AM; Teodorescu, CM; Macovei, D; Enculescu, I; Parvulescu, V; Vasile, E

Published: NOV 15 2008, MATERIALS CHEMISTRY AND PHYSICS, 112, 153, DOI: 10.1016/j.matchemphys.2008.05.023

Iron- and europium-doped (<= 1 at.%)TiO2 nanoparticles powders have been synthesized by a hydrothermal route at 200 degrees C, starting with TiCl4, FeCl3 center dot 6H(2)O and EuCl3 center dot 6H(2)O. The structure, morphology and optical peculiarities were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), Mossbauer spectroscopy and UV-vis measurements. The photocatalytic performance was analysed in the photodegradation reaction of phenol. Rietveld refinements of XRD patterns reveal that the as-prepared samples consist in iron- and europium-doped TiO2 in the tetragonal anatase structural shape, with particle size as low as 15 nm. By means of Mossbauer spectroscopy on both Fe-57 and Eu-151 isotopes as well as by EXAFS analyses, the presence of Fe3+ and/or Eu3+ ions in the nanosized powders has been evidenced. It was found that iron and europium ions can substitute for titanium in the anatase structure. From the UV-vis reflection spectra, by using the transformed Kubelka-Munk functions, the band gap energy (E-g) of the hydrothermal samples has been determined in comparison with that of Degussa P-25 photocatalyst. A decrease of E-g from 2.9eV found for Degussa photocatalyst to 2.8 eV for the titania doped with 1 at.% Fe has been evidenced, indicating a valuable absorption shift (similar to 20 nm) towards visible light region. However, the best photocatalytic activity in the photodegradation reaction of phenol was evidenced for the hydrothermal sample, TiO2: 1 at.% Fe, 0.5 at.% Eu, in both UV and visible light regions. The photocatalytic activities of iron-doped and iron-europium-codoped samples are high and practically the same only in visible light. The photocatalytic properties in Correlation with the structural and optical peculiarities of the hydrothermal samples are discussed. (C) 2008 Elsevier B.V. All rights reserved.