High energy-resolution electron energy-loss spectroscopy and soft-x-ray emission spectroscopy studies of amorphous diamond transformed from neutron-irradiated graphite

High energy-resolution electron energy-loss spectroscopy measurements were performed for amorphous diamond (am-DIA), which was synthesized from neutron-irradiated graphite by shock compression, by using a monochromator transmission electron microscope (TEM). Soft-X-ray emission spectroscopy (SXES) measurements were performed by a wavelength-dispersive type spectrometer attached to the monochromator TEM. A volume plasmon peak of am-DIA is observed at 32.5 eV, which is a little smaller than that of crystalline diamond (c-DIA). The smaller plasmon energy of am-DIA indicates a smaller valence electron density of am-DIA than that of c-DIA. From the onset energies of the K-shell excitation and the SXES spectra, the band gap energy of am-DIA is estimated to be 4 eV, which is similar to the value, 3.9 eV, from the valence electron excitation spectrum and reported values, 3.5-4.5 eV, for the am-DIA synthesized from C60 fullerene by shock compression.