Ar+-sputtered Ge (001) surface nanostructuring at high implant temperature
Abstract
Ion sputtering induced nanoscale pattern formation on Ge (001) surface by 500 eV Ar+ bombardment has been investigated for a wide range of ion incidence angles at temperature of 300 deg.C. A fourfold symmetric topography forms in the angular regime 0 - 65 deg. Above 65 deg, they show a remarkable transition into highly regular one-dimensional (1D) asymmetric pattern, known as perpendicular mode ripples. In order to understand growth dynamics of both kind of patterns, we have investigated their temporal evolution as a function of ion fluence in a wide range from 1*1017 to 1*1020 ions cm-2. In addition, we study the effect of substrate rotation on Ge surface morphology in whole angular range. The four-fold symmetric patterns effect does not found to alter their symmetry, while the ripples degenerate into hole structure with a weak fourfold symmetric pattern. The origin of square topographies and their symmetry independency on ion incident angle in the range 0 to 65 deg can be attributed to the growth process due to biased diffusion of vacancies arising from Ehrlich-Schwoebel barrier. Whereas, the ripple formation at grazing incidence angles indicates the dominance of curvature dependent surface instability induced by the incident ion direction.
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