Sample-morphology effects on x-ray photoelectron peak intensities

The authors have used the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis to simulate photoelectron spectra from the four sample morphologies considered by Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)]. These simulations were performed for two classes of materials, two instrument configurations, and two conditions, one in which elastic scattering is neglected (corresponding to the Tougaard results) and the other in which it is included. The authors considered the Cu/Au morphologies analyzed by Tougaard and similar SiO2/Si morphologies since elastic-scattering effects are expected to be smaller in the latter materials than the former materials. Film thicknesses in the simulations were adjusted in each case to give essentially the same chosen Cu 2p(3/2) or O 1s peak intensity. Film thicknesses with elastic scattering switched on were systematically less than those with elastic scattering switched off by up to about 25% for the Cu/Au morphologies and up to about 14% for the SiO2/Si morphologies. For the two morphologies in which the Cu 2p(3/2) or O 1s peak intensity was attenuated by an overlayer, the ratios of film thicknesses with elastic scattering switched on to those with elastic scattering switched off varied approximately linearly with the single-scattering albedo, a convenient measure of the strength of elastic scattering. This variation was similar to that of the ratio of the effective attenuation length to the inelastic mean free path for the photoelectrons in the overlayer film. For the two morphologies in which the Cu 2p(3/2) or O 1s photoelectrons originated from an overlayer film, the ratios of film thicknesses with elastic scattering switched on to those with elastic scattering switched off varied more weakly with the single-scattering albedo. This weaker variation was attributed to the weaker effects of elastic scattering for photoelectrons originating predominantly from near-surface atoms than for photoelectrons that travel through an overlayer film. (C) 2013 American Vacuum Society. [http://dx.doi.org/10.1116/1.4774214]