Coarsening dynamics at unstable crystal surfaces

In this paper we focus on crystal surfaces led out of equilibrium by a growth or erosion process. As a consequence of that, the surface may undergo morphological instabilities and develop a distinct structure: undulations, mounds or pyramids, bunches of steps, ripples. The typical size of the emergent pattern may be fixed or it may increase over time through a coarsening process that in turn may last forever or it may be interrupted at some relevant length scale. We study dynamics in three different cases, stressing the main physical ingredients and the main features of coarsening: a kinetic instability, an energetic instability, and an athermal instability.