Measuring the energy of the graphite pi + sigma plasmon peak

We examine the graphite plasmon loss structure in reflection electron energy loss spectroscopy (REELS) and XPS with respect to the issue of measuring the energy, Ep, of the pi + sigma plasmon peak. The two spectra differ in shape because they are based on different physical processes. In fact, a static core hole – leading to intrinsic (in addition to extrinsic) losses – exists only for XPS. We show that no single energy can be measured on the two spectra for the pi + sigma peak. Possible procedures to deal with the matter are considered.