Theory of terraced topographies produced by oblique-incidence ion bombardment of solid surfaces

When a solid surface is bombarded with a broad ion beam at a relatively large angle of incidence, the surface often develops a terraced form. We introduce a model that includes an improved approximation to the sputter yield and that produces a terraced surface morphology at long times for a wide range of parameter values. Numerical integrations of our equation of motion reveal that the terraces coarsen as time passes, just as observed experimentally. We also show that the terrace propagation direction can reverse as the amplitude of the surface disturbance grows. This highlights the important role higher order nonlinearities play in determining the propagation velocity at high fluences.