Chemical state analysis of carbon alloys using soft x-ray synchrotron radiation

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For the development of advanced functional carbon materials, it is important to understand the origin of their functions from the view point of electronic/molecular structures. We have therefore investigated their electronic structure and chemical-state using soft x-ray synchrotron radiation. In this study, we have achieved (1) the data base formation of x-ray spectra of various fundamental carbon compounds as basic research, and (2) chemical-state analysis of various industrial carbon materials as applied research.(1) Soft x-ray database :Soft x-ray emission spectra of various polycyclic aromatic hydrocarbons (PAH) were measured using synchrotron radiation. From their spectral features, the new relation between the peak features and the molecular size. This indicates that nano-size or hydrogenation ratio of nano-graphite can be easily estimated from the soft x-ray emission spectra. This can therefore be proposed as a new method to evaluate the nano-size of nano-graphitic carbon materi … More als.(2) Chemical state analysis of industrial carbon materials :Carbon films on the Japanese smoked roof the "Ibushi-Kawara" were characterized by high-resolution soft X-ray spectroscopy using synchrotron radiation. By comparing the soft x-ray emission and absorption spectra of Kawara with the reference carbon compounds, it was determined that the carbon films on Kawara consist of mostly carbon-black-like sp_2 carbon atoms and that the surface also contains polyethylene-like sp_3 carbon atoms. The take-off/incident-angle dependence on the x-ray emission/absorption spectra of Kawara shows that the carbon-black-like sp_2 carbon atoms partially form a layer structure oriented parallel to the basal clay plane, and that the degree of orientation of the carbon films is estimated to be 50% that of highly oriented pyrolytic graphite (HOPG). The microstructure of the carbon films on Kawara is one in which half of the carbon-black-like sp_2 carbon atoms form layer-structured clusters parallel to the basal clay plane and the rest of the carbon atoms form random-structured clusters which rigidly connect the layer-structured clustersSoft x-ray emission spectra in the BK and CK regions of Ru/B_4C multilayers under the x-ray standing-wave conditions, aiming at nondestructive chemical-bonding-state analysis of the interlayers. The Ru/B_4C multilayer samples were selectively excited by the monochromatized undulator radiation with on the Bragg reflection condition around 360 eV and off- conditions which were sufficiently higher energy to BK and CK thresholds. Spectral feature differences excited between on-Bragg-reflection-condition and on the off-conditions were symmetrically changed against the excitation energy around the Bragg reflection condition. This symmetrical spectral feature should indicate the chemical-bonding-state difference between the interlayers and bulk layers in the Ru/B_4C multilayers.The electronic structure transition between the semiconducting and metallic states in boron (B)-doped diamonds was element-selectively observed by soft x-ray emission and absorption spectroscopy using synchrotron radiation. For lightly B-doped diamonds, the B2p-density of states (DOS) in the valence band were enhanced with a steep-edge-feature near the Fermi level, and localized acceptor levels, which is characteristic of semiconductors, were clearly observed both in B2p- and C2p-DOS in the conduction bands. For heavily B-doped diamonds, the localized acceptor levels developed into extended energy levels and the new energy levels generated formed an extended conduction band structure that overlapped with the valence band. Thus, the metallic energy band structure is actually formed by heavy boron doping. These valence and conduction band structures observed by soft x-ray emission and absorption spectroscopy accounted for the electrical properties of B-doped diamonds. Less