Efficient Silver Diabolo Hollow Notch Plasmonic Nanotweezer with Improved Heat Sink Capability

A plasmonic nanotweezer with a diabolo hollow notch (DHN) structure is proposed by adding a metal thin film at the bottom of a metal diabolo aperture (DA) nanostructure. The bottom metal film enables the nanotweezer to utilize screening effect and accumulate more free charges near the central corners of the top surface. Consequently, enhanced electric field enables the nanotweezer to trap particles near the top surface when incidented with relatively low-power beam. Silver (Ag) was selected as the metal due to the fact that Ag is much cheaper than gold (Au). Moreover, Ag provides similar thermal conductivity compared to Au. Thus, cost-effective Ag based DHN nanostructure can dissipate heat from the hot region quickly while avoiding particle damage and thermophoresis. Additionally, Ag offers greater reflectivity which can further enhance the screening effect. In this work, we analyzed optical properties of Ag DHN nanotweezer based on structural parameters and proposed an optimized design for efficient nanoparticle trapping. Based on our analyses, the proposed nanotweezer had trapping stiffness (kx, ky, kz) of ~13.7, ~15.4, and ~96 fN/nmWμm−2, respectively. Moreover, Ag DHN nanotweezer can trap a polystyrene sphere of 100 nm diameter with minimum source intensity of 1.9 mWμm−2 which is 66% lower than that required for Ag DA nanotweezer.