Sputtering of copper by 20 keV Noble gas ions at low temperatures

Abstract

Single crystals of copper and polycrystalline copper were bombarded at normal incidence with 20 keV Ar +- and Ne +-ions at various temperatures between 30° and 320°K. The sputtering ratio, S, for Ar +-ions on polycrystalline targets as well as on monocrystalline surfaces showed no temperature dependence within the accuracy of measurements between 80° and 350°K. This is attributed to the surface contamination caused by Ar itself, especially at lower temperatures. Bombardment with Ne +-ions in the temperature range between 30° and 350°K on polycrystalline Cu and on (111) and (100) single crystal surfaces showed a very pronounced temperature dependence below 200°K. Apparently Ne diffuses through Cu lattices so easily that no serious surface contamination or lattice distortion arises. An explanation is given on the basis of internal focusing mechanisms inside the crystal. A steep decrease in S observed below 150°K is related to the diffusion of the so-called B interstitials in the Cu lattice. On this assumption, the measurements yield an activation energy of (0.29±0.02) eV for the diffusion process. A second steep decrease of the sputtering coefficient below 50°K can be due to the decreased diffusion of A interstitial copper atoms (activation energy 0.1 eV). A sharp rise in S going from about 100°K to 50°K probably corresponds to an increasing saturation of the copper lattice with Ne. This was verified by measurement of the gas content present in the targets following bombardment.