Raman spectra of graphite oxide and functionalized graphene sheets.

We investigate Raman spectra of graphite oxide and functionalized graphene sheets with epoxy and hydroxyl groups and Stone-Wales and 5-8-5 defects by first-principles calculations to interpret our experimental results. Only the alternating pattern of single-double carbon bonds within the sp2 carbon ribbons provides a satisfactory explanation for the experimentally observed blue shift of the G band of the Raman spectra relative to graphite. To obtain these single-double bonds, it is necessary to have sp3 carbons on the edges of a zigzag carbon ribbon.