The morphology and structure of as-prepared graphene oxide samples (GO-1 and GO-3) were investigated via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As presented in Fig. 2, the scanning electron microscopy (SEM) images of GO sheets were cast on a gold coated (100 nm) Si/SiO2 substrate. All the GO samples were well-exfoliated with a majority of the flakes being only a few layers thick and several micrometers in diameter. In the GO-3 sample, we found that the graphene flakes have rough surfaces than the GO-1 samples. Furthermore, in the TEM observation (inset, Fig. 2), GO-1 shows a layer-by-layer stacked structure, while GO-3 has wrinkled paper like morphology. Such morphological changes can be attributed to the increased formation of phenolic and epoxy functional groups on the basal plane of GO-3. Topographic images of the GOs are shown in Fig. 3 together with the height profiles. AFM images confirm that GO-1 and GO-3 are comprised of isolated few-layer sheets. GO-1 and GO-3 have lateral dimensions of several micrometers and a thickness of 1–3 nm, which is characteristic of a fully exfoliated graphene oxide sheet. Furthermore, we clearly observed from the AFM images that the GO-3 sheet has rougher edges than GO-1. Typical AFM analyses disclose the same morphology of GO-1 and GO-3 as that obtained from the SEM and TEM measurements.