Repeatable switching of the bending direction of ZnO nanoneedles by ion beams

We studied the ion beam bending of ZnO nanoneedles to find the dependence of their bending direction on the ion beam energy and to clarify the bending mechanism. Through gallium focused ion beam (FIB) bending, the stems of the nanoneedles were found to be bent to the direction of the ion beam source for ion beam energies of 30 keV whereas they were bent in the opposite direction at ion energies lower than 20 keV. We found for the first time that the bending direction of ZnO nanoneedles could be changed by repeated switching of the ion beam energy between lower and higher energy levels, and that the thin tip parts of the nanoneedles were bent toward to the ion beam source like the higher energy bending mode during the process of lower energy bending below 20 keV. Through high resolution transmission electron microscopy (HRTEM) observations of the microstructure of a nanoneedle, bent by 30 keV higher energy ion beams, based on the atomic scale, we found that more edge dislocations were created in the rear side, deeper than the central plane of the nanoneedle, than the front side and that each edge dislocation added an extra lattice plane in this region. These observations clearly showed that the bent nanoneedles were plastically deformed by the edge dislocations created by the ion beams.