On the origin of sputtered excited atoms

Abstract

The formation of excited neutral atoms in the sputtering process can be understood by considering the inelastic energy transfer, ΔEe, in the final collision associated with the sputtering of a surface atom. We take ΔEe as proportional to the kinetic energy, E:ΔEe ≃ KE. If ΔEe is partitioned randomly amongst all accessible excited states, the result for the yield of the i th state is yield=2giUKΣk=i∞ Gk-1 (ε{lunate}k-1 - ε{lunate}k+1-1), where gi is the degeneracy, U is the surface binding energy, Gi is the cumulative degeneracy (namely, Gi=g0+g1+g2+...+gi), and ε{lunate}i is the excitation energy. Such an expression is approximately of exponential form, i.e. yield ∝ exp( -ε{lunate}i kT*), where T* is a parameter with units of temperature. It is shown that this approach describes relative yields rather well, and that it describes absolute yield ratios (such as those of Tsong and Yusuf) to within a factor of three. © 1982.