Nanoscale observation of a single graphene oxide layer using scanning tunneling microscopy

Nano-scale structures of a single graphene oxide (GO) layer deposited on Au(111) covered with the octanethiolate self-assembled monolayer (C₈S-SAM) have been investigated by scanning tunneling microscopy (STM). Using a spin-coating method, we found that GO akes are isolated and are dispersed on the C₈S-SAM/Au(111) surface whereas these are likely to pile up on the bare Au(111) surface. Furthermore, the C₈S-SAM formed on Au(111) enables us to deposit GO keeping the surface clean even if we prepared the sample in the atmosphere. By using the C₈S-SAM/Au(111) substrate, we succeeded in observing an STM image of the unreduced GO. The STM image of a single GO layer exhibits the grain-like structure having the range in height from 0.6 to 1.1 nm. The bias-dependent STM study indicated that the STM image of GO is stably and reproducibly obtained at the voltage where the density of states of GO exists.