Search

Differential and total photoemission cross-section of oriented orbitals are evaluated for a short-range atomic potential and their dependence on the energy and the polarisation of the incident radiation is discussed.

Publisher Summary The photoelectron spectroscopy has become one of the most powerful tools for the investigation of electronic structure and various excitation processes in solids and on their surfaces. By developing the angle-resolved ultraviolet (ARUPS) regime for probing valence states the band structure of solids has been separated from theory to become a real experimental observable. In primary stages of this experimental band mapping it is shown that photoemission data can be successfully interpreted within the framework of the direct transition model in terms of the single particle approximation via the so-called three step model. Photoemission process is divided into three independent steps: photoabsorption, propagation of the photoelectron to the surface and its subsequent escape across it. The photoabsorption step is described as transition under influence of the photon field between two stationary bulk electronic states and a photocurrent is given by the golden-rule formula. Instead of a set of delta functions the observed ARUPS spectra takes form of the set of finite size peaks whose widths cannot be simply attributed to the instrumental resolution of the experimental device.

Publisher Summary Complicated many-electron problem can be reduced to the one-electron problem if only the elastic channel of the incident/excited electron is investigated. The effective potential, so called optical potential, is no more real; its imaginary component is responsible for the electron absorption (damping) in the elastic channel. Elastic collisions of electrons, being responsible for the loss of investigated electron from the elastic channel, cause the effective absorption or damping of the electron flux. This central factor of surface sensitivity is usually treated in a well-simplified manner, however, by adding an imaginary constant contribution to the real potential to obtain the optical potential. This is in a marked contrast to the real part of the potential in which crystalline periodicity is fully respected. The simplified description appeared sufficient for surface crystallography by low energy electron diffraction (LEED) and for determining of electron dispersion relations E( ) by angular resolved photoemission. Damping of excited electron states in crystals, complementing dispersion relations E( ), can be obtained from profiles in LEED and angular resolved photoemission. The damping should be treated more carefully for subtler effects, and in particular at very low energies.