Nanopatterning graphite by ion-beam-sputtering: Effects of   polycrystallinity
  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. 
Sun Mi Yoon, J.-S. Kim, D. Yoon, H. Cheong, Y. Kim, H. H. Lee
cond-mat.mes-hall cond-mat.mtrl-sci