Information depth for elastic-peak electron spectroscopy

We present a formalism for calculating the information depth (ID) for elastic-peak electron spectroscopy (EPES) in which a measurement is made of the intensity of elastically backscattered electrons for an amorphous or polycrystalline material and a selected electron energy. IDs and a related quantity, the mean penetration depth (MPD) for the detected electrons, were computed from Monte Carlo simulations and a simple single-scattering model for two elemental solids, copper and gold, at energies between 100 and 10,000 eV for a common EPES measurement configuration. Similar calculations were made as a function of emission angle for an electron energy of 1000 eV. The IDs and MPDs from the Monte Carlo simulations were generally smaller than found from the single-scattering model. The deviations are due in part to neglect of multiple scattering in the analytical model and often to strong variations of the differential cross section for elastic scattering for scattering angles within the acceptance solid angle of the analyzer. Reasonable agreement was found between the computed IDs for gold at an energy of 1000 eV (corresponding to detection of 90% and 95% of the total detected EPES signal) and values estimated from EPES experiments in which Au overlayers were deposited on a Ni substrate. Computed MPDs for copper and gold at energies between 100 and 10,000 eV were found to be smaller than mean escape depths for Auger electrons from these solids, but generally not by as much as expected from the single-scattering model for EPES and from neglect of elastic scattering of the Auger electrons. Multiple-elastic scattering is significant in EPES, and Monte Carlo simulations provide a convenient means for determining the IDs and MPDs for different materials, electron energies, and measurement configurations.