Modifying graphene's lattice dynamics by hot-electron injection from single gold nanoparticles

Two-dimensional layered materials like graphene pave the way to advanced (opto-) electronic devices. Their extraordinary properties can be further controlled employing plasmonic nanostructures. The interplay between two-dimensional material and plasmonic nanostructures yields enhanced light focusing, large absorption cross sections, and hot-carrier generation due to the excitation and decay of localized surface plasmons. However, this interplay strongly depends on the particle's environment and geometry mandating the investigation of individual structures. Here, we show that Raman spectroscopy reveals locally resolved information about charge transfer, temperature, and strain distribution of graphene sheets in the vicinity of individual spherical gold nanoparticles. Hot-electrons are efficiently injected into graphene under resonant excitation of the localized surface plasmons of the gold nanoparticle. Additionally, heating of the graphene sheet and its intrinsic strain can be separated and quantified. Hence, the presented analysis provides unprecedented insights into the underlying microscopic physics enabling better device design in the future.