Convex and concave nanodots and lines induced on HOPG surfaces by AFM voltages inambient air

Abstract

Convex and concave nanodots were created on highly oriented pyrolytic graphite (HOPG)in ambient air by applying a voltage pulse between a metal-coated atomic force microscope(AFM) tip and the sample surface. Using a linear scan with a positive substrate bias,nanoscale lines were also etched on the HOPG surface. Depending on the amplitude andduration of the voltage pulse, the nanostructures are either convex or concave. The depthof the concave structure sharply increased with the amplitude and duration ofthe voltage pulse, while the height of the convexity stayed at a low level andvaried in a small range with the voltage lower than a threshold value. Undernegative substrate bias or in a vacuum, no change occurred on the HOPG surface inthe experimental range. The formation of the nanostructures can be ascribedto the primary dissociative adsorption of water and oxygen in air induced bythe intensive hole concentration and the subsequent defect-assisted oxidation ofgraphite.