THEORY OF ANGLE-RESOLVED X-RAY PHOTOEMISSION BY MULTIPLE-SCATTERING CLUSTER METHOD .3. EFFECTS OF POTENTIAL AND DAMPING

The ARXPS formula derived from the first principles many-body theory is applied to two different adsorbed systems Si (111)-(square-root 3 x square-root 3) Ga and Sn, to study their Ga 2p and Sn 3d spectra. Special emphasis is placed on the effects of potentials to calculate the scattering phase shifts. Two static potentials are used here; the Watson's neutral pushed back charge potential and the crystal potential. Beyond the static approximation, we also investigate the optical potential. In the forward scattering the optical potential plays an important role for Ga 2p spectra (365 eV), but it is not so important for Sn 3d spectra (765 eV) because of the high energy scattering. In the large-angle scattering the potentials play a minor role. Other factors such as electron damping, thermal vibration, a finite acceptance angle and charge transfer between adatoms and substrate atoms are also discussed. We find that the first and the third factors play an important role to reduce the anisotropy but the main features are unchanged by these factors. Interlayer distance between the adsorbed Sn layer and the first Si layer is predicted to be 1.8 approximately 2.0 angstrom from the present ARXPS analyses.