Dispersion of the Valence Electron Energy Loss in ThinAmorphous Carbon Films deposited by Ion AssistedEvaporation of Graphite

The dispersion of electron energy loss with transferred wave vector q has been measured for amorphous, non-hydrogenated carbon films. The peak energies for both the loss peak related to the main plasmon loss and for that brought about by the $\pi\rightarrow\pi^{\ast}$ interband transitions are found to follow a power law in q. The films exhibited differences of the exponents which may be related to structural differences. For the material deposited with very small ion flux, which is quite similar to ordinary evaporated carbon, a dispersion of the two low loss peaks with q1.6 and q1.9, respectively, has been found whereas in the case of the other two films, the dispersion appears to be nearly linear in q.