Plasma bands in graphite

The π + σ plasmons in a strongly oriented pyrolitic graphite were studied experimentally using the characteristic electron energy loss technique with an angular resolution in the reflection mode. It was established that the bulk intralayer π + σ plasma bands have two branches with a positive and a negative dispersion, respectively. Each dispersion branch of the π + σ plasmons is a doublet. The interlayer plasmons are characterized by a positive dispersion coefficient only. The results are interpreted qualitatively based on the special features of the electronic band spectrum of graphite. The doublet arises because both dipole and multipole interband transitions similar in intensity are excited in graphite exposed to electron bombardment.