Nanoscale reduction of graphene oxide under ambient conditions

Localized voltage-induced reduction, initiated by a conductive atomic force microscope probe under ambient conditions, is used to pattern electrically conductive reduced graphene oxide (rGO) regions in electrically insulating graphene oxide (GO). This method is shown to reduce single and multiple layer GO on ultra-flat Au substrates with feature sizes as small as 4.0 nm, with the reduction resolution depending strongly on humidity and number of GO layers. In situ current levels during reduction are used to track reaction kinetics, which follow a rate-limited process where the generation and transport of hydrogen ions are the primary rate limiting steps. Tip-enhanced Raman spectroscopy is used to map the nanoscale structure and local disorder in voltage-reduced GO and rGO single sheets. It is found that reduction of GO causes a decrease in tip-enhanced Raman scattering intensity in both the D-band and G-band, but the D/G intensity ratio remains unchanged following reduction, indicating that defects are not introduced by the reduction process. (C) 2015 Elsevier Ltd. All rights reserved.