Center for Functional Nanomaterials Seminar

Characterization of the electronic states of valence electrons (bonding electrons) is imperative for characterizing new functional materials. Furthermore, it is expected with high special resolution and based on microscopy. For that purpose, soft-X-ray emission spectroscopy (SXES), which is caused especially by transitions of valence electrons to inner-shell core-hole states, combined with transmission electron microscopy should be the best way. We have been developing SXES instruments for a conventional analytical transmission electron microscope (TEM). Those spectrometers are a wavelength-dispersive type but do not disturb the spatial resolution of a TEM, because those do not have a moving mechanism as in the case of wavelength-dispersive spectrometers of EPMA. Each spectrometer was composed of laminar-type varied-line-spaced (VLS) gratings, a back-illumination CCD detector without anti-reflection coating and X-ray collection mirrors. Carbon K-emission spectra of single crystals of diamond, graphite and monomer C60 show dominant peak assigned to σ-bonding states. Those are different for diamond and graphite due to different σ-bond lengths for the materials. The spectrum of monomer C60 crystal, which is formed by weakly bonded fullerene molecules (curved graphene sheet), shows the σ-bonding states almost at the same energy with that of graphite. Shoulder structures of the C60 spectrum indicated by vertical arrows correspond to π-bonding states. Those are assigned to hu (right hand side) and hg+gg (left hand side) states of the band diagram of C60 monomer crystal. It is seen a characteristic gap between the π-bonding and the σ-bonding states.