Raman Spectroscopy of Substrate Effects on Single- and Twisted-bilayer Graphene

Investigation of substrate effects of twisted-bilayer graphene is critical for the fundamental understanding and the potential applications of tBLG. We obtained high-quality graphene and tBLG by chemical vapor deposition. Si3N4 has been shown to be the best deposit substrate for graphene transistor application. Graphene on Si3N4 tends to have smaller compressive strain than graphene on SiO2, while annealing at 400 °C in ultra-high vacuum results in similar compressive strain and reduced electron doping due to polymer removal.