On the Angular Dependence of Bombardment Induced Light Emission

Abstract

Ion bombardment of solid targets leads to the emission of light either from sputtered or backscattered particles or from the solid materials [1]. Since a fraction of the sputtered particles leaves in some excited state and participates in the photon emission, it is of interest to compare the dependence of the sputtering yield on various parameters with the analogous dependence of light emission. Though the mechanisms of sputtered-atom excitation are not well understood, it is often assumed that the energy distributions of sputtered atoms in the excited state and in the ground state are identical. This implies that the light intensity from the sputtered atoms should be proportional to the total sputtering yield as it is evident from the energy dependence of light intensity measurements [2]. However, some recent experiments [3, 4] show that such a correspondence may not be always valid. In this communication, the angular dependence of excited atom yields is compared , to that of the total sputtering yield in order to test further the relation of atomic excitation with the sputtering process. Qualitatively, a typical angular dependence of photon yield curve is found to be similar to that of the neutral sputtering yield, i.e. the yield first rises monotonically with θ, the angle of ion incidence with respect to the surface normal, passes through a maximum at θ typically 60°-80° and then decreases sharply as θ approaches 900. For not-toooblique incidence, Sigmund [5] predicted a (cos θ) f dependence rather than the normally expected (cos θ) -1 trend, where 1 < f < 2. Quite recently, Yamamura [6] proposed an empirical formula containing two adjustable parameters for the angular dependence of sputtering yield covering the whole angular range. One of the parameters corresponds to Sigmund's f, while the other is related to O.