Abstract: A method for measuring the binding rigidity of free-standing graphene from the dependence of the short-wavelength spectral range of transverse structural fluctuations of a crystal is proposed. The fluctuation spectrum is measured according to the variation in electron-diffraction patterns derived in a transmission electron microscope while tilting the sample.

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: 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: The growth features of FeCr2S4 spinel single crystals prepared by chemical vapour transport were studied by means of scanning electron microscopy, transmission electron microscopy, high resolution electron microscopy, electron diffraction and X-ray analysis. Our results indicate that the epitaxial growth of the new phases FeCr7S12 and FeCr8S12, both based on the NiAs structure, can essentially inhibit the growth of large FeCr2S4 spinel single crystals in the octahedral habit. The new phases are fully characterised and the effects of defect ordering in these new phases are also reported.

Abstract: The fluorination of La2CuO4 can lead to different oxyfluoride compounds depending on the TF2 temperature of the fluorine gas treatment. When 150-degrees-C T(F2) less-than-or-equal-to 200-degrees-c less-than-or-equal-to 200-degrees-C a superconducting material is obtained. Previous neutron diffraction experiments as well as the EXAFS measurements at the La L(III) edge indicate that extra anions lie in an interstitial site between the two (LaO) layers. Electron diffraction patterns clearly show the existence of an incommensurate modulation due to the presence of shear planes. A second phase is also pointed out which can be obtained as a major component when the fluorination temperature is raised to 230-degrees-C. This phase which is not a superconductor crystallizes with the monoclinic symmetry.

Abstract: We examine the propagation of the recently discovered electron vortex beams in a longitudinal magnetic field. We consider both the Aharonov-Bohm configuration with a single flux line and the Landau case of a uniform magnetic field. While stationary Aharonov-Bohm modes represent Bessel beams with flux- and vortex-dependent probability distributions, stationary Landau states manifest themselves as nondiffracting Laguerre-Gaussian beams. Furthermore, the Landau-state beams possess field- and vortex-dependent phases: (i) the Zeeman phase from coupling the quantized angular momentum to the magnetic field and (ii) the Gouy phase, known from optical Laguerre-Gaussian beams. Remarkably, together these phases determine the structure of Landau energy levels. This unified Zeeman-Landau-Gouy phase manifests itself in a nontrivial evolution of images formed by various superpositions of modes. We demonstrate that, depending on the chosen superposition, the image can rotate in a magnetic field with either (i) Larmor, (ii) cyclotron (double-Larmor), or (iii) zero frequency. At the same time, its centroid always follows the classical cyclotron trajectory, in agreement with the Ehrenfest theorem. Interestingly, the nonrotating superpositions reproduce stable multivortex configurations that appear in rotating superfluids. Our results open an avenue for the direct electron-microscopy observation of fundamental properties of free quantum-electron states in magnetic fields.