Nano-machining of highly oriented pyrolytic graphite using conductive atomic force microscope tips and carbon nanotubes

Sub-100 nm holes were made on a highly oriented pyrolytic graphite ( HOPG) surface using a metal-coated atomic force microscope (AFM) tip and carbon nanotube. HOPG was used as a substrate ( work piece) and a metal-coated (10 nm Cr/30 nm Au) Si AFM tip served as the other electrode. A negative voltage pulse was applied to the AFM tip to fabricate holes as small as 10 nm in diameter on the HOPG surface with a depth of 0.34 nm, which corresponds to a single layer of graphene. We also explored an individual multi-walled carbon nanotube (MWNT) attached to the AFM tip for nanoscale machining. Unlike the pyramidal shape of the AFM tip, the high aspect ratio of a carbon nanotube can make it possible to form deeper holes at even smaller surface diameter. The hole-formation mechanism is related to the chemical reaction of graphite with adsorbed water and tunneling electrons from the tip to substrate.