Abstract: Electron energy loss spectra in conjunction with near-edge fine structures of purely stoichiometric niobium monoxide (NbO) and niobium pentoxide (Nb2O5) reference materials were recorded. The structures of the niobium oxide reference materials were checked by selected area electron diffraction to ensure a proper assignment of the fine structures. NbO and Nb2O5 show clearly different energy loss near-edge fine structures of the Nb-M-4,M-5 and -M-2,M-3 edges and of the O-K edge, reflecting the specific local environments of the ionized atoms. To distinguish the two oxides in a quantitative manner, the intensities under the Nb-M-4,M-5 as well as Nb-M-2,M-3 edges and the O-K edge were measured and their ratios calculated. k-factors were also derived from these measurements.

Abstract: An epitaxially grown heterostructure consisting of alternating layers of LaMnO3 (8 unit cells) and SrMnO3 (4 unit cells) on a SrTiO3 substrate has been studied by a combination of electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM) on an atomic scale. Excitation edges of all elements are captured with subnanometer spatial accuracy, and parametrized to obtain chemical profiles. The fine-edge structure of O K and Mn L-2,L-3 edges are interpreted as signatures of the local electronic structure and show a spatial modulation of the concentration of holes with O 2p character. The chemical concentration is found to be different for the bottom and top interface of a SrMnO3 layer. HRTEM complements the EELS results and confirms the asymmetry of the interfaces. (C) 2001 American Institute of Physics.

Abstract: Electron energy loss spectroscopy was used to investigate the bonding of plasma deposited carbon films. The experimental conditions include the use of a specific collection angle for which the shape of the spectra is free of the orientation dependency usually encountered in graphite due to its anisotropic structure. The first quantification process of the energy loss near-edge structure was performed by a standard fit of the collected spectrum, corrected for background and multiple scattering, with three Gaussian functions followed by a comparison with the graphite spectrum obtained under equivalent experimental conditions. In a second approach a fitting model directly incorporating the background subtraction and multiple scattering removal was applied. The final numerical results are interpreted in view of the deposition conditions of the films and the actual fitting procedure with the related choice of parameters.

Abstract: This paper aims to give an overview of the technique of energy-filtered transmission electron microscopy (EFTEM). It explains the basic principles of the technique and points to the relevant literature for more detailed issues. Experimental examples are given to show the power of EFTEM to study the chemical composition of nanoscale samples in materials science. Advanced EFTEM applications like imaging spectroscopy and EFTEM tomography are briefly discussed. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Using the combination of an electron biprism and an energy filter, the coherence distribution in an inelastically scattered wave-field is measured. It is found that the degree of coherence decreases rapidly with increasing distance between two superimposed points in the object, and with increasing energy-loss. In a Si sample, coherence of plasmon scattering increases in vacuum with the distance from the edge of the sample. (c) 2006 Published by Elsevier B.V.

Abstract: Expandable graphite of two types was synthesized by (1) hydrolysis of graphite nitrate of II stage and (2) anodic polarization of graphite in 60% HNO3. Exfoliated graphite samples were produced by thermal shock of expandable graphite samples in air at 900 °C. A comparative study of microstructural distinctions of both expandable and exfoliated graphite samples was carried out using X-ray diffraction, Raman spectroscopy, electron energy loss spectroscopy and high resolution transmission electron microscopy.

Abstract: We have studied the evolution of the structural modulation in epitaxial, c-axis-oriented, Bi2Sr2-xLaCuO6+delta thin films when varying the La content x and for a given x as a function of oxygen content. A series of thin films with 0 <= x <= 0.8 has been prepared in situ by rf-magnetron sputtering and characterized by R(T) measurements, Rutherford backscattering spectroscopy, transmission electron microscopy, and x-ray diffraction techniques. The oxygen content of each individual film was varied by thermal annealing across the phase diagram. The evolution of the structural modulation has been thoroughly studied by x-ray diffraction in determining the variation of the amplitude of satellite reflections in special two axes 2 theta/theta-theta scans (reciprocal space scans). It is shown that the amplitude of the modulation along the c axis decreases strongly when x increases from 0 to 0.2. It is demonstrated that this variation is essentially governed by La content x and that changing the oxygen content by thermal treatments has a much lower influence, even becoming negligible for x > 0.2. Such study is important to understand the electronical properties of Bi2Sr2-xLaxCuO6+gamma thin films.

Abstract: We report the complete disappearance of the structural modulation in heavily lead-doped Bi2-xPbxSr2CaCu2O8+delta crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x = 0.8, corresponding to an effective lead content of x = 0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (beta phase) have been studied and compared to those of undoped crystals displaying the modulated phase (alpha phase). Magnetisation measurements reveal that the irreversibility field H-irr(T) and relaxation rates are strongly improved within the beta phase. Measurements of the lower critical field, H-cl, show that the anisotropy factor, E, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the a phase and P phase coexist. The enhanced pinning is not only due to the alpha/beta interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: We present a Ginzburg-Landau theory for a two-band superconductor with emphasis on MgB2. We propose experiments which lead to identification of the possible scenarios: whether both sigma- and pi-bands superconduct or sigma-alone. According to the second scenario a microscopic theory of superconducting MgB2 is proposed based on the strongly interacting or-electrons and non-correlated pi-electrons of boron ions. The kinematic and Coulomb interactions of sigma-electrons provide the superconducting state with an anisotropic gap of s(*)-wave symmetry. The critical temperature T-c has a non-monotonic dependence on the distance r between the centers of gravity of sigma- and pi-bands. The position of MgB2 on a bell-shaped curve T-c (r) is identified in the overdoped region. The derived superconducting density of electronic states is in agreement with available experimental and theoretical data. It is argued that the effects of pressure are crucial to identify the microscopic origin of superconductivity in MgB2. Possibilities for increase of T, are discussed.

Abstract: We study the properties of a capacitive 13.56 MHz discharge with a mixture of Ar/C₂H₂ taking into account the plasmochemistry and growth of heavy hydrocarbons. A hybrid model was developed to combine the kinetic description for electron motion and the fluid approach for negative and positive ion transports and plasmochemical processes. A significant change in plasma parameters related to injection of 5.8% portion of acetylene in argon was observed and analyzed. We found that the electronegativity of the mixture is about 30%. The densities of negatively and positively charged heavy hydrocarbons are sufficiently large to be precursors for the formation of nanoparticles in the discharge volume.

Abstract: We report the complete disappearance of the structural modulation in heavily lead-doped Bi2-xPbxSr2CaCu2O8+delta crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x = 0.8, corresponding to an effective lead content of x = 0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (beta phase) have been studied and compared to those of undoped crystals displaying the modulated phase (alpha phase). Magnetisation measurements reveal that the irreversibility field H-irr(T) and relaxation rates are strongly improved within the beta phase. Measurements of the lower critical field, H-c1, show that the anisotropy factor, epsilon, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the alpha phase and beta phase coexist. The enhanced pinning is not only due to the alpha/beta interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: Sr2FeMoO6/SrTiO3/CoFe2 trilayers grown by pulsed laser deposition on SrTiO3 (001) are investigated by transmission electron microscopy and electron energy loss spectroscopy. The stack is epitaxial, independent of whether the CoFe2 electrode is grown at 500 or at 50 degrees C. Thus it is possible to obtain epitaxy near room temperature. The SrTiO3/CoFe2 interface is quite sharp, while the Sr2FeMoO6/SrTiO3 interface presents regions of Fe depletion. The chemical composition of the films is close to the nominal stoichiometries. These results could be useful for the growth of heteroepitaxial devices and magnetic tunnel junctions. (C) 2007 American Institute of Physics.