COMPARISON OF THE ATTENUATION LENGTHS AND THE INELASTIC MEAN FREE-PATH FOR PHOTOELECTRONS IN SILVER

The overlayer method for determining the attenuation length was simulated by the Monte Carlo method. The theoretical model was based on the elastic scattering cross sections resulting from the partial wave expansion method. Multiple elastic electron collisions in the solid were considered. Calculations were made for MgKa excited silver 3d photoelectrons ejected in the silver overlayer. The overlayer was “deposited” on a number of substrates having a wide range of atomic numbers. It was found that the values of attenuation length cover a wide interval (9.14—13.44 Å). The inelastic mean free path for Ag 3d photoelectrons assumed in calculations was equal to 13 A. This effect is due to elastic photoelectron collisions. It turned out that the attenuation length depends on the substrate material, the range of the considered overlayer thickness, and the geometry of measurements. Thus, the overlayer experiment can provide any value of the attenuation length for considered photoelectrons from the above interval by suitable selection of the experimental conditions. The results obtained here, together with experimental problems in producing well characterized thin films, explain the scatter in the published experimental values of the attenuation length. The reliability of the theoretical model is extensively discussed. © 1990, American Vacuum Society. All rights reserved.