National Institute Of Materials Physics - Romania

Epitaxial growth of Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y (BZN) thin films was achieved on (100)(pc) LaAlO3 substrate by pulsed laser deposition (PLD) and by chemical solution deposition based on Pechini process. Effect of bismuth and zinc deficiency on the BZN thin films obtained by PLD was discussed, in relation with the starting target composition. Dielectric permittivity and bandgap values were determined from electrical and spectroscopic ellipsometry measurements performed on randomly oriented films grown on Pt/Si substrate. BZN thin films obtained by PLD exhibit, at 100 kHz, a dielectric constant of epsilon(r) = 203 and quite low dielectric losses of tan delta = 5 x 10(-2). Epitaxial ferroelectric - dielectric KTa0.65Nb0.35O3 (KTN) -Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y (KTN on BZN and BZN on KIN) bilayers were obtained by PLD on (100)(pc) LaAlO3 with the insertion of a suitable buffer layer of KNbO3 in the case of KTN on BZN. Such multilayer heterostructures with an epitaxial growth control of each layer are promising candidates for potential integration in microwave devices. (C) 2011 Elsevier B.V. All rights reserved.

Different hybrid structures were obtained by coating magnetic nanoparticles of perovskite type manganite at optimal doping (La0.67Sr0.33MnO3, LSMO) with different quantities of polypyrrole (PPy). The amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by high resolution transmission electron microscopy (HRTEM) and analyzed by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements in near edge structure (XANES) techniques. By analyzing the magnetic behavior of the samples one can observe that the surface modification of magnetic nanoparticles by PPy results in an increase in the saturation magnetization of the composites. The process is ascribed to paired electrons transferred from the delocalized p states of the PPy into the outer disordered layers of the manganite. The analysis of pre-edge peak of the Mn K-edge XANES spectra in the case of PPy coated LSMO nanoparticles indicates that the charge transfer between polymer and nanoparticles is (directed) going to missing or distorted oxygen positions, hence increasing the 3d electrons' mobility and orbital hybridization between the neighboring manganese ion. As a consequence, within the surface layers of LSMO nanoparticles, both energy bands disrupted the structure, and the double exchange process between Mn ions was reestablished determining the saturation magnetizations and pre-edge features increase, respectively. (C) 2012 American Institute of Physics. [doi:10.1063/1.3686662]

This study presents a correlated study of structural, reactivity, and magnetic properties of ultrathin Fe layers grown on Si(001) by molecular beam epitaxy in ultrahigh vacuum. The interface reactivity is characterized by Auger electron spectroscopy. The surface structure is characterized by low electron energy diffraction with spot profile analysis. The magnetism of the synthesized layers is investigated by magneto-optical Kerr effect. At room temperature, metal Fe layers with poor long-range order are synthesized; these layers are ferromagnetic with an extremely low coercitive field (below 1 Oe). The reactivity with Si is low in this case, with formation of an interface layer of about 8 angstrom Fe equivalent thickness with about 7 at.% Si diffused. Samples synthesized at higher temperatures (500 degrees C) exhibit better long-range order, though the Fe reactivity with Si is higher and leads to the formation of an interface compound whose approximate stoichiometry is very close to Fe(3)Si. Once this compound is formed (for an equivalent Fe thickness of about 14 monolayers), disordered metal Fe islands are developing with subsequent Fe deposition, which contain also about 8 at.% Si diffused. These structures exhibit a much lower ferrimagnetism, with saturation magnetization about one order of magnitude lower than in the case of the room temperature synthesis. In this case of high temperature synthesis, two phases are observed, a ferrimagnetic one and a superparamagnetic one.

Structural aspects and atomic intermixing processes in Be/W bilayers deposited on Si(0 0 1) substrates with Fe buffer layers enriched in the (57)Fe Mossbauer isotope have been studied via atomic force microscopy, grazing incidence X-ray diffractometry, X-ray reflectometry, X-ray photoelectron spectroscopy and conversion electron Mossbauer spectroscopy. The mentioned investigations allowed a full sequential characterization of the involved interfaces. Various ionic configurations appeared for Fe or W, while an amorphous state was observed in the case of Be. It has been proven that the Be layer has a negative influence on the roughness of the whole structure, which however presents an oxidation gradient from more oxidized elements at the surface towards more reduced elements in deeper layers. A strong diffusion of the W atoms inside the Be layer, induced by the deposition method, as well as of the Fe atoms inside the Be layer, induced by thermal annealing, has been evidenced. (C) 2011 Elsevier B.V. All rights reserved.

Manganese is deposited onto GaAs(001) substrates in high vacuum conditions (10(-7) hPa), with substrates held at 300 degrees C. It is shown that this procedure yields to the diffusion of magnanese into gallium arsenide and the formation of a layer which exhibits room temperature ferromagnetism, with highly diluted Mn (below 1 atomic percent). X-ray absorption fine structure determinations at the Mn and Ga K-edges evidenced that Mn is not placed into substitutional Ga sites in GaAs. Most probably, Mn forms MnO clusters with rocksalt local structure. These clusters are the origin of the detected ferromagnetism.

The band (or Stoner) ferromagnetism in systems exhibiting a linear density of states, such as a graphene sheet, where the density of states g(e) is proportional to e, is investigated as function of temperature. The calculations are performed by neglecting spin-wave excitations and some arguments are presented for this approximation. It is found that the occurrence of ferromagnetism becomes easier at finite temperature than in the low temperature limit, especially for systems with low values of carrier density. An almost linear dependence of the magnetization on temperature is predicted; the temperature of vanishing magnetization is linear with the value of the equilibrium Fermi energy, irrespective of the value of the interaction (Hubbard) parameter. Also, for low values of the Hubbard energy an increase in the average value of the polarization with the temperature is predicted in the range of low temperatures. The most important application of such systems consists of control over the onset of magnetization by the charge density (the value of the Fermi energy).

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 X-ray 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.

This work presents recent studies concerning the synthesis of ultrathin ferromagnetic Fe layers on Si(001) and the correlated follow-up measurement of their structural properties, interface reactivity, and magnetism. This study is undertaken as function of the amount of Fe deposited and of substrate temperature. The interface reactivity is characterized by Auger electron spectroscopy. The surface structure is characterized by low electron energy diffraction (LEED). The local order of Fe atoms is investigated by X-ray absorption fine structure (XAFS) and the magnetism by magneto-optical Kerr effect (MOKE). A general trend established is that a higher deposition temperature stabilizes a better surface ordering, but also enhances Fe and Si interdiffusion and therefore decreases the magnetism. A surprising effect obtained by Fe deposition at room temperature is that, despite the rapid disappearance of the long range order with Fe deposition (no LEED pattern is observed for Fe coverage exceeding one monolayer), the material exhibits a significant uniaxial in-plane magnetic anisotropy. When the deposition is performed at high temperature (500 degrees C), a weak ferromagnetism is still observed, with saturation magnetization of about 10 % of the value obtained for room temperature deposition. The combined MOKE and EXAFS studies allowed inferring consistent values for the range of Fe thicknesses where the reaction takes place and the main properties of the distinct formed layers.

Inhibitive properties of the antibacterial sulfa drug sulfathiazole-IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide-on the corrosion of carbon steel in 1.0M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe3+ oxide/oxyhydroxide consisting of a mixture of Fe2O3, alpha, and gamma-FeO(OH) and/or Fe(OH)(3), where alpha, gamma-FeO(OH) is the main phase.

Caesalpinia pulcherrima (Linn) popularly known as Peacock flower in India belongs to family Caesalpiniace. In this work, we describe environment friendly technique for green synthesis of gold nanoparticles from AuCl4 solution using the Caesalpinia pulcherrima (Peacock flower) flower extract as reducing agent. The gold nanoparticles were characterized using UV-visible spectroscopy and transmission electron microscopy (TEM). The UV-visible spectra indicate a strong Plasmon resonance that is located at similar to 450 nm. The TEM analysis shows that products have spherical morphology with size ranging between 10-50 nm. The study also indicates that gold nanoparticles show good antimicrobial activities when compared to the standard antibiotics.