Convex-concave nanostructure transition on highly oriented pyrolitic graphite surface induced by atomic force microscope tip under bias voltage

Convex and concave nanoscale dots were formed on a highly oriented pyrolitic graphite surface in air by an atomic force microscope tip under positively applied bias voltage. It was found that the increasing amplitude or duration of the bias voltage over threshold values can change the convex profiles into concave ones. The threshold voltage duration for the profile transition increases sharply with decreasing amplitude of the voltage and a nonlinear relationship between them was obtained. For enough long duration, there exists a threshold voltage amplitude, about 4.1-5 V in this study, for the profile transition as well.