Surface excitation parameter for allotropic forms of carbon

摘要

The surface excitation parameter (SEP) is calculated for five carbon allotropes: amorphous carbon, graphite, glassy carbon, C_(60)-fullerite and diamond for electron energies between 300 eV and 3400 eV, and for angles between 0° and 60° to the surface normal. SEP, defined as the change in excitation probability, for an electron, caused by the presence of the surface in comparison with an electron moving the same distance in an infinite medium, is calculated within two dielectric response models due to Yubero and Tougaard (YT) and Tung, Chen, Kwei and Chou (TCKC) respectively. We show that SEP results obtained from TCKC are roughly independent of the allotrope while values calculated from YT are clearly material dependent. Moreover we find that SEP calculated from TCKC is on average 40% larger than those calculated from YT, the difference being largest for materials with large band gap energy. This difference is due to the simplified description of surface excitations in TCKC