Microstructuring of Graphene Oxide Nanosheets Using Direct Laser Writing

Graphene(G),a single atomiclayer ofaromatic carbon atoms,has attracted much attention recently owing to its fascinating properties such as massless fermions, ballistic electronic transport, and ultrahigh electron mobility. [1] Currently, there are many approaches to the synthesis of graphene ranging from chemical vapor deposition from hydrocarbon to solution phase methods involving the chemical exfoliation of graphite. [2] One commonly used solution-processing route to graphene involved the chemical reduction of graphene oxide (GO). GO is produced by the oxidative treatment of graphite. [2] The basal planes of GO are decorated with epoxide and hydroxyl groups, while carboxylic and carbonyl groups are located at the edges. These oxygen functionalities render GO hydrophilic and improve its solubility, however they destroy the aromaticity of the graphene framework. As a result, GO is insulating, and a chemical reduction and thermal annealing treatment is needed before electronic conductivity could be recovered. The presence of oxygen functional groups also reduces the thermal stability of GO relative to that of G, since GO can be thermally pyrolized at high temperatures and transformed into volatile carbonaceous oxides. The thermal instability of GO motivates us to consider a strategy for the microstructuing of GO nanosheets using laser-assisted etching. The microstructuring of GO is relevant to the challenges of lithographically patterning G, since GO and G are interconvertible to some extent. Recently, promising approaches for the patterned assemblies of G on substrates have been developed. [3–8] Micro-contact printing using molecular templates was used to transfer GO sheets onto the pre-defined areas of the substrate surfaces via electrostatic attachment. [3] Large-scale G films were recently synthesized on patterned nickel layers using chemical vapor deposition. [7] All the patterning methods reported so far involved conventional lithographic techniques or employment of masks for the definition of patterns on substrates. To date, there are few demonstrations of a maskless, direct ‘‘writing’’ pattern on G-related materials using electron beam or optical methods.