On the problem of whether excited states amongst sputtered particles are of thermal origin

Abstract

Abstract Two models of a thermal nature are currently advocated to explain the presence of ions amongst sputtered particles. In so far as these models are valid, one must consider the possibility that excited neutrals amongst sputtered particles also have a thermal origin, whence that the yields of photons emitted by these excited neutrals will be given by Yield α (ω i /Q) exp(-e i /kT). Here ω i is the degeneracy of a state which lies ε i above the ground state and Q is the internal partition function. We have tested the above equation experimentally and can summarize the results as follows: (a) The equation was satisfactorily obeyed by Be, BeO, Al, Al2 O3, Sc, GaAs, Y, In, and Tl, the inferred temperatures lying in the interval 3600–5900 K. (b) The range of temperatures agrees with four independent estimates from other work, (c) The temperatures are, on the other hand, insensitive to the variation of target mass from 9 to 204 u, ion mass from 20 to 84 u, ion energy from 4 to 16 keV, and target crystallinity, results which are in disagreement with conventional thermal-spike theory. It is concluded that the thermal-excitation model accounts for many of the details of excited-state production but that the inferred temperatures have an origin other than in conventional thermal spikes.