Recovery of monolayer graphene sub-lattice dynamics in photoreduced graphene oxide

Graphene oxides (GO) are a widely-used substitute for graphene’s remarkable mechanical properties, but its highly amorphous lattice lacks desirable electronic properties such as high conductivity, fast photoresponse and broad spectral coverage. To study the evolution of GO to graphene, optical quality GO-polymer films are prepared and then sequentially photoreduced five times by Xe lamp-exposure. The most reduced samples give optical absorption spectra showing the best agreement to the modified Fano lineshape of monolayer-graphene, supporting that the removal of oxygen functional groups recovers monolayer graphene behavior. At each stage of photoreduction, transient absorption kinetic relaxation dynamics of graphene oxide gradually revert to that of concomitantly measured CVD-monolayer graphene. The recovery of ultrafast dynamics matching monolayer-graphene in moderately reduced samples shows the presence of large uninterrupted sp² bonded networks that, for energies ranging from 0.5 to 1.3 eV, are nearly optically indistinguishable from graphene. All data is fit to a supercollision hot-electron cooling model that shows photoreduction systematically increases lattice disorder. By demonstrating that systematic photoreduction of graphene oxide replicates the spectral and hot-electron cooling dynamics of monolayer-graphene a process for convenient large scale production of optical graphene is identified.