Emission statistics of X-ray induced photoelectrons and its comparison with electron- and ion-induced electron emissions

The emission statistics of secondary electrons from a gold metal surface induced by monochromatic X-rays is studied by Monte Carlo simulations. The number distributions of emitted electrons n and their mean values γ are calculated systematically for incident photon energies from 1 to 100 keV. The results are compared with recent experimental results measured at the SPring-8 X-ray beam facility (BL15XU). We found that both theoretical and experimental results of the statistical number distributions of secondary electrons can be reproduced fairly well by Polya-type functions, showing small probabilities for one-electron emission (n = 1) and broad distributions for high-n emission. In contrast, these features can never be reproduced by Poisson statistics. Furthermore, calculated emission yields γ are found to depend rather weakly on the incident X-ray energy. These results indicate clearly that fast photoelectrons produced by high-energy X-rays are responsible for high-n emission although the photoionization cross sections are considerably smaller at higher X-ray energies. Simulations are also extended to electron and ion bombardments, and a comprehensive comparison between X-rays and charged particle impacts is given for the emission statistics of electrons from a metal surface.