Ion Induced Reemission of Noble Gases from a Nickel Surface

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Abstract
Each of the noble gases, He, Ne, A, and Kr, has been ionically pumped with an energy of about 100 ev into a nickel target and has been subsequently released by a similar bombardment using a different noble gas. A mass spectrometer permitted the measurement of both the reemission of the trapped atoms and the trapping of the bombarding particles. The reemission mechanism is described in terms of a simple model which assumes that the trapped atoms are released by the bombarding particles through a mechanism of sputtering of either the target material or the trapped gas or a combination of both. The experimental results are in agreement with the model. A direct replacement of a trapped atom from its trapping site by a bombarding particle is shown to be a relatively unimportant factor in the reemission process. Measurements of the reemission rates of the trapped atoms have yielded information concerning the depth distribution of the trapped atoms in the nickel target. In particular, saturation of the depth distribution has been observed for Ne, A, and Kr at concentrations below one equivalent monolayer while He showed no such effects at the highest concentrations used, which corresponded to approximately 15 equivalent monolayers.