| Popis: |
The electronic excitation spectra at arbitrary momentum values can be determined 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 photoemission measurements, can be avoided. However at such high energies the geometry of the experiment has to be known very accurately. Here we describe a procedure to check the actual geometry of the experiment, and how to adjust for misalignments, if they are present. Spectral momentum densities obtained in this way for graphite along low symmetry directions are compared with full potential linear muffin tin orbital calculations. The measured intensities agree quite well with the calculations, however the observed dispersion of the graphite σ band exceeds the calculated one by 1.5-2 eV, and the separation between s and p band is somewhat smaller in the calculation compared to the experiment. |
