High energy-resolution electron energy-loss spectroscopy analysis of dielectric property and electronic structure of hexagonal diamond

Electron energy-loss spectroscopy measurements of a hexagonal diamond (h-DIA) were performed using a transmission electron microscope equipped with a monochromator. From the measurements, the dielectric function of h-DIA was derived using Kramers-Kronig analysis (KKA) for the first time. The results of KKA showed that the band gap energy of h-DIA was 4.2 eV, which is 1.3 eV smaller than that of a cubic diamond (c-DIA). The peak energies that appeared in the imaginary part of the dielectric function were assigned to the interband transition energies predicted by theoretical calculations. The K-shell excitation spectrum of h-DIA, which was apparently different from that of c-DIA, also showed good agreement with the reported theoretical prediction.