Propagation of ripples on pyrochlore induced by ion beam bombardment

Abstract

The morphological evolution of ripples formed on the surface of ${\text{Cd}}_{2}{\text{Nb}}_{2}{\text{O}}_{7}$ pyrochlore single crystals by focused ion beam bombardment was investigated using in situ electron microscopy. At high ion fluences and off-normal bombardment angles, faceted surface ripples with a ``terracelike'' structure were observed. The ripple propagation direction was oriented along the projected ion beam direction at incident angles ranging from 35 to $65\ifmmode^\circ\else\textdegree\fi{}$ under high-dose ion bombardment. One side of the terrace was found to be perpendicular to the incident ion beam direction, while the other side was parallel to the ion beam. The terrace propagation velocity and direction were determined and interpreted on the basis of this asymmetric structure. A model based on the propagation of a shock wave that effectively ``self-selects'' a stable slope was developed in order to explain the observed faceted ripple formation.