Abstract: We present an efficient method for the quantification of crystalline versus amorphous phase content in mesoporous materials, making use of electron energy loss spectroscopy. The method is based on fitting a superposition of core-loss edges using the maximum likelihood method with measured reference spectra. We apply the method to mesoporous TiO2 samples. We show that the absolute amount of the crystalline phase can be determined with an accuracy below 5%. This method takes also the amorphous phase into account, where standard X-ray diffraction is only quantitative for crystalline phases and not for amorphous phase. (c) 2006 Elsevier B.V.. All rights reserved.

Abstract: We propose an improved image simulation procedure for atomic-resolution annular dark-field scanning transmission electron microscopy (STEM) based on the multislice formulation, which takes thermal diffuse scattering fully into account. The improvement with regard to the classical frozen phonon approach is realized by separating the lattice configuration statistics from the dynamical scattering so as to avoid repetitive calculations. As an example, the influence of phonon scattering on the image contrast is calculated and investigated. STEM image simulation of crystals can be applied with reasonable computing times to problems involving a large number of atoms and thick or large supercells.

Abstract: The structure and defect structure of superconducting ferromagnetic bulk RuSr2GdCu2O8 has been investigated using high-resolution transmission electron microscopy and high-resolution scanning transmission microscopy. Two distinct, but closely related structures, due to ordering of rotated RuO6 octahedra and due to Cu substitution in the Ru-O layer, have been revealed. The structure of Ru1-xSr2GdCu2+xO8-delta can be described as a periodic alteration along the c axis of CuO4 planes and RuO6 octahedra. The unit-cell parameters of this phase are root 2a(p) x root 2a(p) x 2c. The possible influence of this phase and defect structure on the sensitivity of the superconductivity and magnetic properties is discussed. Local defects such as 90 S domain boundaries, (130) antiphase boundaries, and the associated dislocations are analyzed.

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: The measurement of the electronic structure of anisotropic materials using energy loss near edge structure (ELNES) spectroscopy is an important field of microanalysis in transmission electron microscopy. We present a novel method to study the angular dependence of electron inelastic scattering in anisotropic materials. This method has been applied to the study of 1s -> pi* and sigma* transitions on the carbon K edge in pyrolitic graphite. An excellent agreement between experimental and theoretical two-dimensional scattering patterns has been found. In particular, the need of a fully relativistic calculation of the inelastic scattering cross-section to explain the experimental results is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: Glass ceramic composites were prepared by bulk crystallization of NaNbO3 in sodium niobium borate glasses. A homogeneous bulk crystallization of the NaNbO3 phase takes place during heat treatments that produces visible-near infrared transparent materials with similar to 30 nm NaNbO3 nanocrystallites. Upon thermal poling, a strong Na+ depleted nonlinear optical thin layer is observed at the anode side that should induce a large internal static electric field. In addition, the chi((2)) response of the poled glass ceramic composites increases from 0.2 up to 1.9 pm/V with the rate of crystallization. Two mechanisms may be considered: a pure structural chi((2)) process connected with the occurrence of a spontaneous ferroelectric polarization or an increase of the chi((3)) response of the nanocrystallites that enhances the electric field induced second harmonic generation process. (c) 2006 American Institute of Physics.