Effect of Thin Carbonaceous Films on 500-keV Helium Ion Sputtering of Copper

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Abstract
A radioactive tracer technique capable of measuring less than 10−10 g of copper has been developed. A 500-keV magnetically analyzed beam of helium ions is used to observe the sputtering yield as a function of carbonaceous film thickness over a copper target. It is shown that an amorphous film of the order of 2×1017 atoms/cm2 reduces the sputtering yield of copper by a factor of 100. A first collision model of sputtered atom penetration of the film is in good agreement with the data and yields a copper—carbon cross section of 3×10−17 cm2. A clean surface sputtering yield of 2×10−2 atoms/ion is obtained by extrapolation of the data and is consistent with the yield of 800-keV D+ sputtering of copper reported by Kaminsky [Phys. Rev. 126, 1267 (1962)]. It is postulated that ordering of the amorphous film occurs for areal densities greater than 2×10+17 atoms/cm2 on the basis that the rate of reduction of copper yield with increasing film thickness undergoes a sharp decrease at that point.

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