Nanometer ripple formation and self-affine roughening of ion-beam-eroded graphite surfaces

The topography of (0001)-graphite (highly oriented pyrolytic graphite) surf aces eroded by a 5 keV Xe+ ion beam has been investigated using scanning tu nneling microscopy. For tilted incidence of the ion beam and ion fluences o f about 10(17) cm(-2), a quasiperiodic ripple topography with characteristi c wavelengths between 40 and 70 nm has been found. As predicted by continuu m theory and Monte Carlo simulations, below a critical angle theta(C) the r ipples are oriented perpendicular to the ion beam projection onto the surfa ce, while for angles above theta(C) the ripple orientation is parallel to t he ion beam projection. The critical angle theta(C) lies between 60 degrees and 70 degrees, in agreement with the predictions of the continuum theory. For rising ion fluences, large scale perturbations of the surface topograp hy occur indicating a nonlinear behavior governed by the Kardar-Parisi-Zhan g universality class. [S0163-1829(99)50628-0].