Energy transfer from rare gases to surfaces: Collisions with gold and platinum in the range 1-4000 eV.

Abstract

We have measured the energy transferred to a gold surface by impinging ${\mathrm{He}}^{+}$, ${\mathrm{Ar}}^{+}$, and ${\mathrm{Xe}}^{+}$ ions with kinetic energies in the range 5\char21{}4000 eV. This same quantity has been determined for He, Ar, and Xe atoms colliding with a Pt(111) surface. The ion studies employed a novel highly sensitive pyroelectric calorimeter together with a carefully designed compact ion gun. Pulses of nearly monoenergetic ions from the gun were directed at a gold film evaporated directly onto a pyroelectric material that develops a voltage proportional to the energy deposited. The atomic studies were made with supersonic beam techniques, whereby energy transfer is inferred from time-of-flight distributions of the incident and scattered species. The results from these very different experiments are in good agreement and give a fairly complete picture of energy transfer from incident rare-gas atoms and ions to these heavy-metal surfaces. For energies above about 10 eV, the ions transfer at least 60% of their energy, with Xe transferring the most and He the least. For lower incident energies, the energy transfer decreases, approaching zero-energy intercepts of \ensuremath{\sim}60%, 20%, and 5% for Xe, Ar, and He, respectively. The implications of these experimental results for the effective-mass concept, the binary-collision model, low-energy stopping powers, lattice penetration, and the theory of physical sputtering are considered, and we address the relevance of these findings to the technologically important processes of plasma etching and deposition of sputtered thin films and to particle-spacecraft interactions and controlled thermonuclear fusion.