Electronic structure of crystals via VLEED

Abstract

Dispersion relations E(k) of electrons in crystals preserve their meaning in many-electron systems. Interacting electrons become quasiparticles, which apart from energies, are also characterised by lifetimes. As for real systems these characteristics are difficult to evaluate, some experimental evidence is desirable. Attention will be focused on two methods applicable at energies above the vacuum level. Interaction of external beam of slow electrons with crystals in target current spectroscopy (TCS), and in very low energy electron diffraction (VLEED), will be discussed in context with the unoccupied part of the electronic band structure. Knowledge of electron dispersion relations above the vacuum level is important for interpretations of angular resolved photoelectron spectroscopy. Comparison of experimental TCS and VLEED data with theoretical band structure calculations determines positions of energy gaps and more detailed theoretical interpretations of the intensity profiles provides information about electron lifetimes in metals and semiconductors.