Angle resolved XPS study of inhomogeneous specimens of polycrystalline silver covered with uniform graphite overlayers

The depth dependence of the XPS peak shape parameter is determined experimentally for inhomogeneous specimens of the type f(x) = 0 for x0 > x > 0 and f(x) = constant for x > x0, where f(x) is the electron emitter concentration as a function of depth (x) and x0 is the overlayer thickness. In order to do this, specimens with sharp interfaces are prepared by depositing uniform overlayers of graphite on flat surfaces of polycrystalline silver. The peak shape parameter thus determined is found to be a function of the overlayer thickness. The observed dependence has been explained in terms of the existing first order analytical expression for this parameter. Angle resolved studies have also been done to explore the possible contributions arising out of surface excitation losses. Such studies clearly pointed out the presence of such an effect. Experimental results are discussed with a special emphasis on the possible sources of systematic errors which may contribute to the measured values of this parameter.