Determination of the anisotropic electronic structure of graphite by (e,2e) spectroscopy

The electronic excitation spectra at arbitrary momentum values can be deter mined in principle by (e,2e) spectroscopy. These experiments are performed using high energy electrons (1 keV up to 20 keV) meaning that refraction of electrons at the surfaces, a complicating factor for low energy photoemiss ion measurements, can be avoided. However at such high energies the geometr y of the experiment has to be known very accurately. Here we describe a pro cedure to check the actual geometry of the experiment, and how to adjust fo r misalignments, if they are present. Spectral momentum densities obtained in this way for graphite along low symmetry directions are compared with fu ll potential linear muffin tin orbital calculations. The measured intensiti es agree quite well with the calculations, however the observed dispersion of the graphite sigma band exceeds the calculated one by 1.5-2 eV, and the separation between s and p band is somewhat smaller in the calculation comp ared to the experiment.