Nanostructured arrays of stacked graphene sheets

Abstract

Molecular oxygen etching of HOPG surfaces prepatterned by GaC focused-ion-beam irradiation (FIB) has been used to generate large-area arrays of nanometer-sized graphite blocks. AFM and SEM imaging show that structures with lateral sizes down to 100 nm and heights of between 30 and 55 nm can be routinely fabricated. The trenches separating the graphite blocks form in the early oxidation stages via preferential gasification (into CO and CO2) of the gridlike amorphized carbon regions written by FIB. In the later oxidative etching stages, gasification of the graphite nanoprism faces laterally terminating the graphite blocks becomes the major reaction channel. Correspondingly, graphite blocks are (further) reduced in lateral extent while the trenches in between are widened. Raman and photoionization spectroscopies indicate that the quality of the topmost nG sheet(s) covering the blocks also decreases with increasing etching time?as the size and lateral density of defect-mediated etch pits increases. nG block arrays are useful substrates with which to probe the size-dependent properties of nanographene, as they comprise large numbers of uniform sheets(4x10^10 cm^2 for an array of 0.5x0.5 um^2) thus allowing for the application of area-integrating spectroscopic methods. We demonstrate this by examining the Raman features of nG block arrays which include a graphene-rim-region fingerprint mode. Individual nG sheets can be exfoliated from nG stacks by means of electron-irradiation-induced charging. We have explored a number of printing/manipulation strategies aimed at controllable electromechanical transfer of nG sheet arrays to silicon wafers.