Electron Microscope Examination of the Surface Topography of Ion-Bombarded Copper

Transmission electron microscopy of thin, polycrystalline copper foils has revealed the formation of a sputtering structure after bombardment at normal incidence with Xe+ Cu+, or Pb+ ions of 50 to 80 keV energy. In general, the surface of each individual grain degenerates into a "hill and valley" structure, so as to develop those {100} faces lying nearest to the plane of the surface. The sputtering structure has been found to be independent of any prior electropolishing surface structure. Similarity between the spacing and crystallographic direction of the sputtering structure, and the general appearance of the dislocation arrays produced by ion bombardment, suggests that these dislocations could influence the initiation of the structure. A tentative model based on this hypothesis is proposed to account for the periodicity of the observed sputtering effect.