Escape probability of s-photoelectrons leaving aluminium and copper oxides

Abstract

The escape probability of O 1s and Al 2s photoelectrons from Al2O3 and CuO overlayers grown on Al and Cu substrates, respectively, has been studied as a function of photoelectron depth of origin and emission direction. Escape probabilities have been determined experimentally, analytically and by a Monte Carlo method. The analytical approach is based on solution of a kinetic equation satisfying appropriate boundary conditions. Both the Monte Carlo calculations and analytical theory account properly for multiple elastic and inelastic scattering of photoelectrons on their way out of the target. The results are compared with those of the straight-line approximation (SLA), where elastic scattering is neglected. It has been found experimentally that the escape probability as a function of depth of origin for the O 1s photoelectrons leaving Al2O3 surface at an emission angle of 60° with respect to the incident x-ray beam direction can be approximated by an exponential function. In contrast, the escape probability of s-photoelectrons in a direction close to that of x-ray propagation exhibits non-monotonic behaviour, with a maximum at a depth of 4–10 Å. The experimental data agree well with the predictions of Monte Carlo simulations and analytical theory, and differ noticeably from the SLA results. © 1998 John Wiley & Sons, Ltd.