Band gap engineering of graphene oxide by chemical modification

The method with which one creates a sample of graphene oxide paper has a strong impact on its electronic structure. Using X-ray emission spectroscopy and X-ray absorption spectroscopy to indirectly measure the band gap, we have found that intercalation with hexylamine increases the band gap, while replacing water with dimethyl sulfoxide (DMSO) decreases the band gap. Reduction with hexylamine sharply decreases the band gap as expected, but we have also found that heating the sample reduces the band gap to the same degree. This band gap reduction is due to defunctionalization of graphene oxide via reaction with water that produces CO2. Direct current four-probe conductivity measurements show that the decrease in band gap width leads to a lower-than-expected increase in conductivity, likely because the heat-induced defunctionalization process destroys the graphene sheet and reduces overall carrier mobility.