Molecular-Scale Plasmon Trapping via a Graphene-Hybridized Tip-Substrate System.

We theoretically investigated the plasmon trapping stability of a molecular-scale Au sphere via designing Au nanotip antenna hybridized with a graphene sheet embedded Silica substrate. A hybrid plasmonic trapping model is self-consistently built, which considers the surface plasmon excitation in the graphene-hybridized tip-substrate system for supporting the scattering and gradient optical forces on the optical diffraction-limit broken nanoscale. It is revealed that the plasmon trapping properties, including plasmon optical force and potential well, can be unprecedentedly adjusted by applying a graphene sheet at proper Fermi energy with respect to the designed tip-substrate geometry. This shows that the plasmon potential well of 218 kT at room temperature can be determinately achieved for trapping of a 10 nm Au sphere by optimizing the surface medium film layer of the designed graphene-hybridized Silica substrate. This is explained as the crucial role of graphene hybridization participating in plasmon enhancement for generating the highly localized electric field, in return augmenting the trapping force acting on the trapped sphere with a deepened potential well. This study can be helpful for designing the plasmon trapping of very small particles with new routes for molecular-scale applications for molecular-imaging, nano-sensing, and high-sensitive single-molecule spectroscopy, etc.