Dynamic scaling of ion-sputtered surfaces

4 pages, 2 figures.-- PACS nrs.: 79.20.Rf, 64.60.Ht, 68.35.Rh.We derive a stochastic nonlinear equation to describe the evolution and scaling properties of surfaces eroded by ion bombardment. The coefficients appearing in the equation can be calculated explicitly in terms of the physical parameters characterizing the sputtering process. We find that transitions may take place between various scaling behaviors when experimental parameters, such as the angle of incidence of the incoming ions or their average penetration depth, are varied.R.C. acknowledges a postdoctoral fellowship of the Spanish Ministerio de Educación y Ciencia.Publicad