Spatially-Resolved Ultrafast Optical Spectroscopy of Polymer-Grafted Residues on CVD Graphene

A recent report proved that polymer residues become grafted to graphene despite the efforts to clean the surface by thermal annealing [Lin, Y.-C., et al. Nano Lett. 2012, 12, 414]. Such residues inevitably originate from the photoresist (e.g., poly(methyl methacrylate) (PMMA)) used for graphene transfer and device processing. Here, through spatially resolved transient absorption spectroscopy and transient photoluminescence spectroscopy, we investigate the effects of such polymer-grafted residues on the carrier dynamics of CVD graphene. The presence of these polymer-grafted residues is validated by both X-ray photoelectron spectroscopy and micro-Raman spectroscopy. Unlike the ultrafast nonradiative recombination at the pristine graphene, these regions exhibit distinct long-lived carrier dynamics that undergo radiative recombination, which is characteristic of the opening of the graphene bandgap. Understanding the influence of such defects on the carrier dynamics and relaxation pathways is key to modifying the optoelectronic properties of graphene-based devices.