Abstract
The electrical transport property of the reduced graphene oxide (rGO) thin-films synthesized from defective GO through thermal treatment in a reactive ethanol environment at high temperature above 1000 °C shows a band-like transport with small thermal activation energy (Ea~10 meV) that occurs during high carrier mobility (~210 cm2/Vs). Electrical and structural analysis using X-ray absorption fine structure, the valence band photo-electron, Raman spectra and transmission electron microscopy indicate that a high temperature process above 1000 °C in the ethanol environment leads to an extraordinary expansion of the conjugated π-electron system in rGO due to the efficient restoration of the graphitic structure. We reveal that Ea decreases with the increasing density of states near the Fermi level due to the expansion of the conjugated π-electron system in the rGO. This means that Ea corresponds to the energy gap between the top of the valence band and the bottom of the conduction band. The origin of the band-like transport can be explained by the carriers, which are more easily excited into the conduction band due to the decreasing energy gap with the expansion of the conjugated π-electron system in the rGO.
Highlights
The localized states in the energy gap originating from electron confinement[13] means that many defects remain in the rGO
We found that a high temperature process above 1000 °C in ethanol treatment enables us to overcome this issue from the analysis of carrier transport properties, X-ray absorption fine structure (XAFS), valence band photo-electron spectra observed from rGO films, Raman spectra and transmission electron microscopy (TEM)
The carrier mobilities of the rGO films prepared by ethanol treatment as a function of the process temperatures are evaluated from Hall-effect measurements using the van der Pauw method
Summary
The localized states in the energy gap originating from electron confinement[13] means that many defects remain in the rGO. For device applications utilizing the electrical performance of the intrinsic graphene material with ultra-high carrier mobility, it is necessary to obtain large-area graphene films that show band-like transport (not VRH conduction). We found that a high temperature process above 1000 °C in ethanol treatment enables us to overcome this issue from the analysis of carrier transport properties, X-ray absorption fine structure (XAFS), valence band photo-electron spectra observed from rGO films, Raman spectra and transmission electron microscopy (TEM)
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