Trapping Nanoparticles Using Localized Surface Plasmons of Graphene Nanodisks

Abstract

Given the sub-wavelength trapping challenges in the optical tweezers, the plasmonic tweezers serve as a bridge by breaking the diffraction limit. Hence, the development of plasmonic tweezers can open up many potential applications in biology, medicine, and chemistry. In this paper, using localized surface plasmons (LSPs) of graphene nanodisk with a resonance frequency of 20 THz, we design a lab-on-a-chip optophoresis system, which can be utilized to effectively trap the nanoparticles. The LSPs of graphene nanodisk generate a large field gradient in the deep sub-wavelength area around the resonance frequency. We show that by an appropriate choice of chemical potentials of the graphene nanodisks, the strong optical near-field forces desired for trapping can be generated under the illumination of the THz source when the polystyrene (PS) nanoparticles are located in the vicinity of graphene nanodisks. Numerical simulations show that the designed system with graphene nanodisks of 250 nm in diameter and chemical potentials of µ c = 0.6 eV can trap the PS nanoparticles of 12 nm in diameter and larger with a THz source intensity of 19 mW/µm 2 , demonstrating acceptable sensitivities for variations in the nanoparticle diameter and refractive index. Moreover, at the same source intensity, the graphene nanodisks with µ c = 0.7 eV can trap the PS nanoparticle as small as 9.5 nm in diameter.

Design and Analysis of a Polarization-Insensitive VO2/Graphene Optical Modulator Using a 3D Heat Transfer Method

“…where ε 0 is the permittivity of free space, Δ is the effective thickness of monolayer graphene that is 0.34 nm, ω is the angular frequency of light, and σ is the complex conductivity of graphene. The conductivity of graphene is obtained from the Kubo formalism 5,44,45 je j ( )…”

“…The electromagnetic response of a single graphene layer can be described by its dielectric constant ε g as , where ε 0 is the permittivity of free space, Δ is the effective thickness of monolayer graphene that is 0.34 nm, ω is the angular frequency of light, and σ is the complex conductivity of graphene. The conductivity of graphene is obtained from the Kubo formalism ,, where σ intra and σ inter are, respectively, the intraband and interband conductivities, ℏ is the reduced Plank constant, e is the electron charge, μ c is the chemical potential, and τ is the relaxation time that is taken as 0.5 ps. The chemical potentials of graphene at the on state ( V bias = 0) are assumed to be μ c 1 = μ c 2 = 0.55 eV, which ensure that the graphene sheets are transparent at an operating wavelength of 1550 nm.…”

High-performance Mach–Zehnder modulator using tailored plasma dispersion effects in an ITO/graphene-based waveguide

“…In this regard, the complex dielectric constant of graphene is obtained from 61 : and imported to the simulations as the optical model. The parameter is the effective thickness of graphene that is taken as 0.34 nm, is the permittivity of free space, is the angular frequency and is the complex conductivity that is calculated by the Kubo formula 61 , 62 where the first and second terms on the right hand side are respectively the intraband and interband conductivities, is the reduced plank constant, e is the electron charge, is the relaxation time that is assumed to be 0.5 ps 61 and is the chemical potential. As a result and according to , the average value of graphene mobility in the ON state is approximately /v.s.…”