Cone Formation on Metal Targets during Sputtering

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Abstract
When a Cu surface is sputtered by ion bombardment under the condition that Mo atoms arrive at the Cu surface during sputtering an unexpected phenomenon can arise: The surface of the Cu target becomes covered with microscopic cones. The cone density increases with increasing flux density of arriving Mo atoms. When the cones are closely spaced they give the target a velvet‐like black appearance. The result of dense cone coverage is a lower sputtering yield and a more oblique ejection of sputtered material. The cone tops seem to consist of Mo nuclei which are constantly replenished via surface migration and protect the underlying Cu from being sputtered.