The trapping of low-energy noble gas ions at a tungsten surface

Experimental results, including those of the authors, for the variation with energy below 1 kev of the trapping efficiency S0 for noble gas ions incident upon atomically clean polycrystalline tungsten are discussed and compared. A suggestion by Kornelsen, that the threshold energy (at S0 = 10-5) is determined by the interaction energy between the neutral gas atom and a surface tungsten atom, has been extended and a theory developed enabling a value of S0 to be calculated using the repulsive interaction potentials calculated by Abrahamson. The curves derived from this theory show good agreement with the experimental curves for the four gas-metal combinations He-W, Ne-W, Ar-W and Kr-W. For low energies and low total ion flux, these calculations also indicate the variation of trapping efficiency with the target crystal face presented to the incident ion.