The desorption behaviour of implanted noble gases at low energy on silicon surfaces

Under UHV conditions, clean crystalline Si(111) surfaces have been bombarded mass-selectively at room temperature with noble gas ions, Ne+, Ar+, Kr+, at normal incidence. By means of stepwise heating up to 1050 K the activation energies and desorbed doses of the noble gases have been straight forwardly determined as a function of temperature and bombardment dose. Firstly a short review of the kinetics of desorbed adsorbates is given and compared with a simple model for the desorption of particles embedded in a surface layer. This shows that the rate constant ν in the latter case is orders of magnitude lower and are in agreement with obtained experimental values. From the obtained activation energies we have concluded that these values have to be explained by the silicon properties and that the influence of the noble gas is of second-order importance. The present method enables the simultaneous measurement of both the ellipsometric and desorption spectra during stepwise heating of the sample.