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 kBT 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.

Plasmonic optical tweezers with a symmetry-tunable potential well were investigated based on a heterogeneous model of nano-bowtie antennas made of different noble substances. The typical noble metals Au and Ag are considered as plasmonic supporters for excitation of hybrid plasmonic modes in bowtie dimers. It is proposed that the plasmonic optical trapping force around a quantum dot exhibits symmetry-broken characteristics and becomes increasingly asymmetrical with increasing applied laser electric field. Here, it is explained by the dominant plasmon hybridization of the heterogeneous Au–Ag dimer, in which the plasmon excitations can be inconsistently modified by tuning the applied laser electric field. In the spectrum regime, the wavelength-dependent plasmonic trapping potential exhibits a two-peak structure for the heterogeneous Au–Ag bowtie dimer compared to a single-peak trapping potential of the Au–Au bowtie dimer. In addition, we comprehensively investigated the influence of structural parameter variables on the plasmonic potential well generated from the heterogeneous noble nano-bowtie antenna with respect to the bowtie edge length, edge/tip rounding, bowtie gap, and nanosphere size. This work could be helpful in improving our understanding of wavelength and laser field tunable asymmetric nano-tweezers for flexible and non-uniform nano-trapping applications of particle-sorting, plasmon coloring, SERS imaging, and quantum dot lighting.

We present theoretical investigations on designing a simple double nano-slit superlens for dramatically improving imaging quality for advanced plasmonic photolithography through introducing graphene as a plasmonic integrator. It is proposed that more than 235 times enhancement of localized electric field can be assured as the graphene layer is embedded in the designed superlens. It is observed that by introducing graphene for superlensing, dominant enhancement of electric field amplitudes of interference imaging profiles can be observed at a properly designed photoresist with optimal thickness. We further show by systematically examining design parameters for the graphene-based superlens, clarifying the overall geometric and material parameter influences on the plasmonic imaging pattern characteristics. The results are attributed to the unique role of graphene participating in strong hybrid plasmonic cavity coupling modes for supporting localized electric fields of the nanoslit superlensing. This study shows proper designing of graphene-based optical superlens can potentially realize high-quality, low-cost and simple-realized nano-imaging for advanced plasmonic photolithography applications.

We theoretically investigate a graphene-based heterogeneous plasmonic nano-trench for trapping noble metal and non-metal nanospheres. We propose heterogeneous plasmonic modeling geometry consisting of silver, gold and graphene for functioning plasmonic trapping operating at the near-infrared spectrum. For our designed model, the vertical potential well is 32 times larger than the Brownian motion energy KBT, indicating that the nanosphere can be stably trapped using the graphene covered gold and silver nano-trench structure. By varying the incident laser wavelength and angle of illumination, the gold nanosphere can be trapped stably 40 nm above the bottom of the proposed nano-trench structure. The graphene layer enhances the localized electric field of the nano-trench in comparison to a pure silver and gold nano-trench structure without a graphene layer on top.

In this Letter, we propose the electronic manipulation of localized surface plasmon resonance for active tuning in near-field nanofocusing. We theoretically studied the excited graphene tuning of the nanofocusing field in few-layer graphene ( FLG)-based hybrid nanotips. It is revealed that the normalized enhanced electric field can be significantly promoted to more than 300 times. It is also observed that resonant peaks can be unprecedently modified by the electron state of excited graphene that is embedded in the substrate. It shows the possibility of flexible tuning of plasmon resonances via controlling the electron excitation state of graphene for specific advanced near-field nanofocusing applications.

The tunable localized surface plasmons in novel antenna of Au nanosphere dimer coated by graphene is studied theoretically. We demonstrate the electronic tuning of graphene based Au nanosphere antenna via modifying the Femi level of graphene for realizing active tunable localized surface plasmons. It is found that localized electronic field shows an evident increasing, as the graphene layers increase. The resuts are explained as the more evidently enhanced resonance of localized surface plasmons for multilayer graphene than monolayer graphene nanoantenna when the incident light matches to the resonance wavelength of the Au-graphene hybrid system. In addition, it is revealed there is observable blue-shift for the resonance wavelength when the graphene layers get increased. The study provides basic understanding for tuning graphene based on Au nanosphere antenna for a wide range of applications such as single-molecule fluorescence, SERS and photothermal therapy.