Crystallite size dependence of plasmon energies in polycrystalline graphite observed by reflected electron energy loss spectroscopy

Both the energy losses of pi electron plasmon and valence electron plasmon in polycrystalline graphite have been measured by reflected electron energy loss spectroscopy (REELS). It was found that when crystallites are smaller than 10 nm, the pi plasmon energy is lower than the value estimated from t he valence plasmon energy which directly reflects the density. More over, t here is a correlation between the pi plasmon energy and the relative intens ity of the pi plasmon peak to the elastic peak. Thus, the decrease of the p i plasmon energy was explained by a crystallite size effect such asa decrea se in pi electron density. This REELS technique was applied to estimate the chemical state in carbon films obtained by thermal chemical vapor depositi on (CVD). The two-dimensional distribution of the graphitic carbon was succ essfully measured at a spatial resolution of less than 1 mu m.