Valence band of graphite oxide (Vol. 42, No. 1)

Graphite oxide (GO) has been the subject of intense study for its use in producing cheap and vase amounts of graphene by reduction through chemical or physical methods. Reduced graphite oxides have been used in graphene-based applications such as transparent conducting film (TCF), flexible displays, field effect transistors (FET), supercapacitors, and batteries. Therefore, it is essential to study the fundamental electronic and structural properties of graphite oxide to exploit its possible applications.

This paper investigated the valence band structure of graphite oxide by photoelectron spectroscopy for the first time. The typical sp² hybridization states (π and σ) found in graphite were also observed in graphite oxide. However, the π state near the Fermi level disappeared because of bonding between the π and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to the higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks (O_2p and O_2s) were observed at 8.5 and 27 eV in graphite oxide. The work function of graphite oxide was also first measured using the kinetic energy cut-off of the secondary electrons to be 5.9 ± 0.1 eV. This research results can improve fundamental understanding of graphite oxide for its possible applications.