Progress in quantitative surface analysis by X-ray photoelectron spectroscopy: Current status and perspectives

We give a survey of information needed for quantitative surface analyses by X-ray photoelectron spectroscopy (XPS). We describe four terms (the inelastic mean free path, the effective attenuation length, the mean escape depth, and the information depth) that are commonly used as descriptors of the surface sensitivity of an XPS experiment. Due to the complicating effects of elastic scattering, numerical values for each measure are generally different. Analytical formulae are given for each quantity. We describe procedures for determination of surface composition (with an emphasis on three types of relative sensitivity factors), measurements of overlayer-film thickness, and determination of composition-versus-depth information from angle-resolved XPS. Information is given on measurements of photoelectron intensities and the effects of sample morphology and sample roughness. Sources of data are given for all parameters needed for quantitative XPS. We discuss some major remaining uncertainties in quantitative XPS analyses and describe expected future areas of growth in XPS applications.