Estimation of IMFP except for a constant factor using only XPS background-optimized peak intensities and cross sections

Abstract

A method for estimation of inelastic mean-free path (IMFP or λ) of an unknown material except for an arbitrary proportionality constant c, i.e. λ0(E) in λ(E)=cλ0(E), where E is the electron kinetic energy, has been proposed through iteration of background optimization on an XPS spectrum. The dependence of the i-th core peak intensity pi on its energy Ei given by background optimization is proportional to the product of theoretical photoexcitation cross sections σi and the asymmetry factor ai after analyzer transmission correction. Therefore, any non-parallel behavior between pi and (σi·ai) is ascribed to λ(E). This enables the estimation of λ0(E) using pi and (σi·ai), by assuming the initial λ to be constant, and then repeating background optimization and λ update. Between 700 and 1500 eV kinetic energy (KE) for Au metal, where λ by TPP [Tanuma et al, Surf. Interface Anal., 43,689(2011)], denoted as λTPP, is known to be well approximated by a straight line, λ converges to λTPP within 2.4 % if c is chosen so that both values coincide at 800 eV. This is remarkably satisfactory because only relative peak intensities are involved in a usual practical analysis and because what is requested for surface analysis is to analyze the sample whose properties including λ are yet to be known.