Simulation of time-of-flight spectra in direct recoil spectrometry for the study of recoil depth distributions and multiple scattering contributions

Intensity distributions of atoms ejected from model target surfaces due to ion impact in time-of-flight direct recoil spectrometry (TOF-DRS) have been simulated in order to investigate the depth of origin of recoils and the shape of the low-energy TOF tail. The MARLOWE computer code was used to calculate the trajectories of 2–4 keV Ar+/Ne+ ions impinging on a diamond and an alkane polymer surface. The calculations were converted to actual TOF spectra, which allows comparison with experimental data. The simulation results confirm the high surface sensitivity of DRS and reveal the strong dependence of the sampling depth on the primary ion type and energy. A recoilʹs location in the TOF-intensity tail results from complex multiple-collision mechanisms and is not directly correlated to its depth of origin. In the case of H recoils, the Thomas–Fermi-type potential used to model atomic interactions appears to overestimate the differential recoiling cross-section, which may indicate a breakdown of fundamental assumptions in the interaction potential.