Effect of surface excitations in determining the inelastic mean free path by elastic peak electron spectroscopy

Elastic peak electron spectroscopy (EPES) has been widely used to determine the electron inelastic mean free paths (IMFPs) in solids. In this work the influence of surface excitations in determining the IMFP by EPES is investigated. An extended Drude dielectric function is employed to estimate the probability of surface excitations for incident and reflected electrons by including the recoil effect without the small scattering-angle approximation. Elastic scattering differential cross sections are calculated using phase-shift analysis and the finite difference method for solid atoms with the Hartree-Fock-Wigner-Seitz potential in the Dirac equation. Results of Monte Carlo simulations on the determination of IMFPs from experimental elastic reflection coefficients are presented for Ag and Cu. Our results show that the relative difference between the IMFPs obtained with and without surface excitation may reach 40% for low-energy electrons (˜250 eV). The experimental results, with corrections for surface excitations, are in better agreement with the theoretical data.