Defect Enhanced Efficient Physical Functionalization of Graphene with Gold Nanoparticles Probed by Resonance Raman Spectroscopy

We demonstrate efficient physical functionalization of single layer graphene with Au nanoparticles mediated by in-plane defects in graphene grown by a chemical vapor deposition technique. The effect of an ultrathin Au layer on the single layer, bi layer, and few layer graphene with intrinsic defects was studied by resonance Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). We observed a striking enhancement in the intensity of sharp D and D' bands after sputter deposition of an ultrathin Au layer on graphene. In contrast, G and 2D bands show a lower enhancement in intensity and a change in line width due to the charge transfer from Au to the graphene and strong interaction between the Au and graphene layers, respectively. X-ray photoelectron spectroscopy (XPS) analysis shows a 40% decrease in integrated intensity ratio of sp(3) and sp(2) bands in C-1s spectra after Au functionalization indicating bonding of Au atoms preferentially at the defect sites in graphene. This was further substantiated by HRTEM imaging and position dependent Raman spectral line shape analysis. The calculations of interdefect distance and areal defect density from the Raman analysis on the graphene Au hybrid are in close agreement with the HRTEM analysis. Further, Raman spectral line shape dependence of Au functionalization on the number of layers in graphene reveals that Au functionalized single layer graphene behaves like a pristine bi layer graphene due to strong interaction between Au and the graphene layer. These results open up possibilities for efficient physical functionalization of graphene with foreign atoms through defect engineering for novel applications of graphene in catalysis, biosensors, and optoelectronic and photonic devices.