Nanostructuring the graphite basal plane by focused ion beam patterning and oxygen etching

Ga+ focused ion beam (FIB) patterning was used to structure highly oriented pyrolytic graphite surfaces with square, periodic arrays of amorphous carbon defects (mesh sizes: 300 nm-2 μm). Controlled oxygen etching of these arrays leads to matrices of uniform, orientationally aligned, nm-sized, hexagonal holes. The properties of the resulting hole assembly (hole depths and lateral hole dimensions) have been investigated by means of atomic force microscopy, scanning electron microscopy and FIB sectioning. The hole dimensions and uniformity both depend on the FIB parameters and etching conditions. Etching temperatures from 500 to 700 deg. C were applied. Initial etch rates of up to 106 C s-1 per individual hole were observed when using oxygen pressures of 200 mbar. For an etch temperature of 590 deg. C the rate of etching of individual holes was found to depend measurably on the inter-hole separation. This confirms that the associated reaction kinetics is mediated by the finite diffusion length of reactive oxygen species along the graphite basal plane. Prolonged etching results in hole-hole contact and generation of mesa arrays of controllable size and shape