Monte Carlo simulation of time-of-flight spectra of coaxial impact collision ion scattering spectroscopy applied to MoS2(0001) and SrTiO3(001)

We have synthesized a Monte Carlo program to simulate the time-of-flight (TOF) spectra of coaxial impact collision ion scattering spectroscopy (CAICISS). This program is based on the binary collision model considering inelastic energy loss and follows the incoming and outgoing trajectories for each incident ion from a top surface up to 300 monolayers (MLs) below a surface. The present simulation reproduced well the observed overall TOF spectra from MoS2(0001), whose surface structure was already known. It was also found that the ions backscattered from the atoms located in the depths from top surface down to 150th atom layer contributed to the TOF spectrum. In order to extract quantitative information on surface structures from CAICISS spectra, it is essential to estimate accurately the background originated from the backscattering at the depths. The CAICISS measurement followed by the Monte Carlo simulation was applied to structure analysis of a TiO2-terminated SrTiO3(001) surface prepared by a chemical treatment and confirmed that the topmost layer comprised a TiO2 layer and the SrO fraction was estimated to be less than 5%.