Simulation of time-of-flight spectra in direct recoil spectrometry for thestudy 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 s hape of the low-energy TOF tail. The MARLOWE computer code was used to calc ulate the trajectories of 2-4 keV Ar+/Ne+ ions impinging on a diamond and a n alkane polymer surface. The calculations were converted to actual TOF spe ctra, which allows comparison with experimental data. The simulation result s confirm the high surface sensitivity of DRS and reveal the strong depende nce of the sampling depth on the primary ion type and energy. A recoil's lo cation in the TOF-intensity tail results from complex multiple-collision me chanisms 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 interac tions appears to overestimate the differential recoiling cross-section, whi ch may indicate a breakdown of fundamental assumptions in the interaction p otential. (C) 2000 Elsevier Science B.V. All rights reserved.