The spectra of characteristic energy loss by fast electrons and optical functions for different transmitted wave vectors in graphite

Based on the experimental spectra of energy loss by fast electrons in graphite in the range 0–40 eV, the spectra of complete complexes of optical functions, including the dielectric constant, which are decomposed into components, are calculated for the Г – P directions and four values of the transmitted electron wave vector |q|. The data obtained are compared with the known theoretical bands. It is found that in the indirect interband transitions of graphite excited by fast electrons with |q| > 0, a quasigap is opened in the neighborhood of point P, which increases with |q|.