Mechanism of facet formation on Ni surfaces by sputtering with oxygen ion beams

Surface topographic development by oxygen ion sputtering has been studied by scanning electron microscopy (SEM) for polycrystalline Ni and Cr surfaces. The topography was more developed on an Ni surface than a Cr surface. A facet‐type topography with two faces was developed on an Ni surface by sputtering with 7 keV oxygen ions at off‐normal incidence angles where the sputtered surface is partially oxidized. The surface normal of the one facet face was near 0° and that of the other face was ∽80° to the incident ion beam. The facet angles correlated well with the sputtering rates of the two facet faces because the sputtering rate is minimized at a zero incidence angle and maximized near 80°. A two‐step model for the facet formation is suggested. Initially small oxide islands are formed and act as seeds for the facet formation at the first faceting step. The islands are tilted and faceted as a result of successive surface diffusion in a selected direction due to the surface momentum transfer from the incident ions. At the facet propagation step, the facets grow larger and the summits of the facets are propagated toward the ion beams by the great difference in sputtering rate of the two facet faces. © 1998 John Wiley & Sons, Ltd.