Atomic-force-microscopy nanowriting on ultrathin tetrahedral amorphous carbon films

We report the atomic-force-microscopy (AFM)-based nanolithography writing of surface patterns on ultrathin (<100 nm thick) ta-C films in ambient air and following contact-mode AFM reading of nanoscale topography, nanofriction properties, and local electrical conductivity of the produced nanopatterns. AFM writing of various patterns such as single nanospots, linear nanostructures, and raster images ('nanoletters') is demonstrated, depending on the magnitude and duration of the voltage pulses applied between the ta-C film and conductive probe, and the relative humidity of ambient air. It is found that the AFMtip-assisted nanowriting process occurring under (1) the presence of adsorbed water layers on the ta-Csurface, (2) the applied voltage of >4 V, and (3) the contact pressures in the GPa range results in the formation of a novel carbon phase in a nm-thick surface layer characterized by the lower density, lower mechanical strength, lower electrical conductivity, and increased nanofriction as compared to the original film. The structure of the tip-modified nm-thick layer on the ta-C film is assumed to be a structure of graphite oxide which can be further modified in the presence of water under high contact pressures.