Fundamentals of convergent-beam electron diffraction (CBED) are described. First, the CBED method is explained and an obtained CBED pattern is shown. Then, it is described what kind of crystallographic information can be obtained by the CBED method. The characteristic profiles of higher order Laue zone (HOLZ) reflections are explained by the dynamical diffraction effect. The large angle (LACBED) technique and its application to identify the types of dislocations are given. The coherence effect appearing at the overlapping regions of two CBED disks is explained.
Taking account of X-ray polarization, an atomic scattering factor should be treated as a tensor. The ATS (Anisotropy of Tensor of Susceptibility) scattering results in violation of conventional extinction rules by a screw axis and/or a glide plane. Utilizing the“forbidden reflection”, local anisotropy of the electronic state of an absorbing atom can be investigated near the absorption edge. Physical properties of the ATS scattering involved in recent experimental results are briefly reviewed.
Structure determination from powder diffraction data has developed rapidly over the recent years in Europe and US, and various tools and softwares have been presented to enable us to solve structures from powder diffraction data alone.
Quinohemoprotein amine dehydrogenase (QH-AmDH) from Pseudomonas putida has an αβγ heterotrimeric structure with two heme c groups in the largest α subunit and an unidentified quinone prosthetic group in the smallest γ subunit. The crystal structure of QH-AmDH has been determined at 1.9Åresolution. This revealed a unique feature of the catalytic γ subunit with a novel cofactor cysteine tryptophylquinone (CTQ) and three intra-chain cross-links. These links are unprecedented as they are thio-ether bonds between a sulfur atom of Cys and a methylene carbon atom of an Asp or a Glu.
Silica glass is a promising optical material in the deep-ultraviolet (DUV, -4.1-6.2 eV or 300-200 nm) to vacuum-ultraviolet (VUV, >-6.2 eV or <-200 nm) region since its optical band gap is located at-8 eV. For such a purpose, it is crucial to control its band-edge transparency and optical resistivity against the intense laser radiation of DUV-VUV excimer lasers (KrF ; 5.0 eV or 248 nm, ArF ; 6.4 eV or 193 nm, F2 ; 7.9 eV or 157 nm) . The present article reviews our recent studies on silica glasses irradiated with DUV-VUV excimer lasers, including several topics of the improvement of optical transparency by introducing Si-F terminals, the photostructural change of SiOH groups, the formation and annealing kinetics of laser-induced point-defects involving the role of hydrogen, and the application of F-doped glasses to DUV optical fibers.