Angular distribution and escape probability of sputtered atoms

Abstract

To quantify the importance of the role played by the inherent discontinuity due to the surface, depth of origin, angular and energy distributions of sputtered atoms are calculated, for various mass ratios, on the basis of a Monte Carlo simulation code. Calculations are performed, on a random target, assuming an initially isotropic and E 0 −2-like energy distribution. Surface effect is treated by a mean free path length which depends on depth and direction of the emerging atom, its effect being a decrement in the collision rate and a net average deflection towards the normal to the surface, this being more pronounced as the moving atom becomes closer to the surface. This surface effect plus the role of a planar surface barrier increase the escape probability to the peak below the surface position, particularly for light atoms. Mass dependence of the ejected atoms, with respect to the mass of the matrix, is also analyzed in terms of the angular and energy distributions of the ejected atoms, from a given depth. The transfer energy cross-section plays a role in the opposite direction to that of the angular scattering but differences between a light and a heavy atom can be found. From shallow regions, heavy atoms are more likely to be ejected, for glancing emerging directions but, the opposite happens from greater depths. Energy distribution shows clearly that heavy atoms get to the surface, from greater depths, after having spent more energy.