The Sputtering of High Energy Particles

Abstract

<p>The sputtering of high velocity particles is investigated through analysis by secondary photon emission. During a sputtering event a fraction of the particles emitted from the target are in varying degrees of excitation. These excited states have a finite probability of radiatively decaying back to the ground state. The emitted photon wavelength and intensity is recorded. In addition, the monochromator can be locked onto one particular wavelength and its intensity observed as a function of distance from the target surface. Such intensity distributions are measured for several group IA and IIA metals and fluorides. Their spatial extent, for the most part, is shown to be governed by the atomic transition probability of the excited state under observation.</p> <p>A model is developed to describe the intensity distribution based on the premise that the sputtered particles are distributed in energy and we further propose that excitation in a sputtering event is a threshold process. From the experimental intensity distributions this proposed threshold energy is deduced and is found to be 10¹ - 10³ eV. These relatively high kinetic energies, along with the large sizes of excited states, indicate that their creation involves large energy transfers at or very near the surface. Such events as recoil sputtering may lead to the production of excited states.</p> <p>To this end, calculations on recoil sputtering yields and mean energies are reported which justify the observed high energies and low yields. Further, a comparison, based upon fractional yields, of recoil sputtered atoms and high energy cascade sputtered atoms show that the recoil source provides a larger number of high energy atoms available for excitation. Results relating to recoil implantation yields are also presented. In addition, recoil phenomena is used to explain some preferential effects observed in sputtering and transient effects in secondary photon emission.</p> <p>Finally, the fate of the implanted primary ion is discussed with emphasis on its diffusion behavior in both damaged and undamaged ambient surroundings.</p>