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

Abstract

The topography of (0001)-graphite (highly oriented pyrolytic graphite) surfaces eroded by a 5 keV ${\mathrm{Xe}}^{+}$ ion beam has been investigated using scanning tunneling microscopy. For tilted incidence of the ion beam and ion fluences of about ${10}^{17} {\mathrm{cm}}^{\ensuremath{-}2},$ a quasiperiodic ripple topography with characteristic wavelengths between 40 and 70 nm has been found. As predicted by continuum theory and Monte Carlo simulations, below a critical angle ${\ensuremath{\theta}}_{C}$ the ripples are oriented perpendicular to the ion beam projection onto the surface, while for angles above ${\ensuremath{\theta}}_{C}$ the ripple orientation is parallel to the ion beam projection. The critical angle ${\ensuremath{\theta}}_{C}$ lies between $60\ifmmode^\circ\else\textdegree\fi{}$ and $70\ifmmode^\circ\else\textdegree\fi{},$ in agreement with the predictions of the continuum theory. For rising ion fluences, large scale perturbations of the surface topography occur indicating a nonlinear behavior governed by the Kardar-Parisi-Zhang universality class.