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

抄録

  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 p_i on its energy E_i given by background optimization is proportional to the product of theoretical photoexcitation cross sections σ_i and the asymmetry factor a_i after analyzer transmission correction. Therefore, any non-parallel behavior between p_i and (σ_i·a_i) is ascribed to λ(E). This enables the estimation of λ₀(E) using p_i and (σ_i·a_i), 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 λ_TPP, is known to be well approximated by a straight line, λ converges to λ_TPP 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.