Credit: © 2010 AAAS

Efficiently modifying graphene oxide to make it more like graphene has recently been the focus of much attention in an effort to make best use of its excellent electronic properties and avoid the problems of more direct methods of synthesis. Strategies to do this include the use of reducing agents like hydrazine, and thermal methods whereby simple heating is used. Now, a team led by Paul Sheehan of the US Naval Research Laboratory, and Elisa Riedo of the Georgia Institute of Technology, have miniaturized the thermal treatment method to create defined nanoscale areas of reduced graphene oxide (rGO) within pristine graphene oxide sheets.

The technique they used — thermochemical nanolithography (TCNL) — involves applying an AFM tip to a surface to locally induce a chemical reaction. This approach has previously been used to modify polymer surfaces, but here the tip is applied to graphene oxide. To test the method, squares and crosses of rGO were created on an isolated graphene oxide flake, and it was observed that heating caused a decrease in the thickness of the sheet, which could be explained through the removal of oxygen-containing functional groups and a change in the hybridization of the carbon bonding network – from sp3 to sp2. The degree of reduction can be tuned by controlling the temperature of the tip and this process was confirmed by measuring the surface friction, which decreases on chemical reduction.

TCNL was also used to create a nanoribbon of rGO on a large area epitaxial film of graphene oxide grown on silicon carbide. The zig-zag nanoribbon was approximately 12 nm wide and was shown to be more conductive than the surrounding graphene oxide.