Ripple wave vector rotation in anisotropic crystal sputtering

Surface morphology of a Cu(110) crystal, generated by ion sputtering, has been investigated by scanning tunneling microscopy. Different from recent theoretical predictions and experimental results, normal sputtering produces a well defined ripple structure whose wave vector rotates from [001] to [1 (1) over bar 0] increasing the substrate temperature. Off-normal sputtering at low temperature (180 K) generates ripples whose orientation depends on both ion direction and surface azimuthal orientation. These results are described by a continuum equation which includes both surface curvature dependent erosion terms and diffusion terms accounting for surface anisotropy and Ehrlich-Schwoebel barriers. [S0031-9007(98)07159-2].