Title: “A Study of the Correlation between the Oxidation Degree and Thickness of Graphene Oxides.”

Thickness control is very important to commercial applications of 2D nanomaterials. The thickness of graphene oxide (GO) layers varies depending on the fabrication process, which is directly influenced by the content of oxygen functional groups. In the present study, we investigated the correlation between the thickness and the degree of oxidation of GO through macroscopic and microscopic analysis. In this experiment, four GOs having various degree of oxidation were analyzed by X-ray Photoelectron Spectroscopy (XPS) to evaluate the amount of oxygen functional groups, respectively. A monolayer analysis by Atomic Force Microscope (AFM) and d-spacing analysis by X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) were employed to compare and analyze the effect of the degree of oxidation on the thickness of the GO layers. The results showed that the degree of oxidation had a directly proportional relationship with the thickness and d-spacing of the specimens. Raman spectroscopy was also employed to further verify the proportional relationship between the degree of oxidation and the thickness of the GO specimens. In conclusion the degree of oxidation of GOs can be inversely predicted by analyzing them by Raman spectroscopy, XRD and TEM.