  Employing graphites having distinctly different mean grain sizes, we study
the effects of polycrystallinity on the pattern formation by
ion-beam-sputtering. The grains influence the growth of the ripples in highly
anisotropic fashion; Both the mean uninterrupted ripple length along its ridge
and the surface width depend on the mean size of the grains, which is
attributed to the large sputter yield at the grain boundary compared with that
on terrace. In contrast, the ripple wavelength does not depend on the mean size
of the grains. Coarsening of the ripples-accompanying the mass transport across
the grain boundaries-should not be driven by thermal diffusion, rather by
ion-induced processes.
