A theory of peaks in the time-of-flight spectrum of gold atoms sputtered from a (100) surface

Abstract

The energy and angular spectrum Φ(E, Ω) of sputtered atoms is described as the sum of the contribution of atoms sputtered from the surface and of atoms sputtered from the second plane. Each contribution is factorized into a bulk spectrum Φ′_i(E′, Ω′) for layer i and an inverse sputtering Jacobian [J _i(E, Ω; E′, Ω′)] ⁻¹ which describes the steering effects at the surface layer. The form of these Jacobians is studied by calculating trajectories of atoms sputtered from a gold (100) surface with a molecular-dynamics program MOLDY. Based on the results, estimates of the time-of-flight spectrum predict that the main contribution to sputtering in 〈100〉 is from the second plane of atoms which are steered towards 〈1100〉 by their surface neighbours. The steering causes zeros in J ₂ and hence peaks in the time-of-flight spectrum in 〈100〉 at 156 and 6 eV, energies which are sensitive to the chosen gold-gold potential. The theory explains the origin of the high-energy peak (∼150 eV) in the measurements of Thompson, Reid and Farmery (1978). To account for the double-peak structure observed at low energy in these experiments, the effect of anisotropy in the bulk spectrum Φ′(E′, Ω′) is also considered.