Soft X-ray absorption near-edge structures of B/C and B/C/N materials and the analysis of their electronic state using first-principles calculations

Graphite-like layer materials composed of boron/carbon (B/C) and boron/ carbon/nitrogen (B/C/N) have been prepared by chemical vapor deposition (CVD). In order to evaluate the electronic states of these materials, the X-ray absorption near-edge structures (XANES) of the materials have been measured and analyzed by first-principle calculation using the "discrete variational (DV)-Xα molecular orbital method". Absorption intensities of the CK-edge XANES spectra for B/C and B/C/N materials started to increase at energies 1.1 eV lower than that of graphite, which suggests that the energy levels of the conduction bands of B/C and B/C/N materials were lower than that of graphite by 1.1 eV. DV-Xα calculation suggests that co-valent bonds between boron and carbon atoms lower the bottoms of the conduction bands of these materials, compared with that of graphite. Since electron affinity is defined to be the difference between the vacuum level and the bottom of the conduction band, these results indicate that B/C and B/C/N materials have larger electron affinities than that of graphite. Consequently, the present study supports the experimental results which have been reported for the donor-type intercalation of Na, Mg and Ca into B/C and B/C/N materials.