Corrugated Gold Tip as Optical Tweezers to Apply Force on Zinc Sulphide Quantum Dot Nanoparticle

One of the most important issues after synthesizing colloidal quantum dot nanoparticles is how to use them. In some cases, a very small number of these nanoparticles is needed. One of the ways to remove small amounts of these nanoparticles is to use a tip-shaped plasmonic optical tweezer made of metal. This work is dedicated to the improvement of the near-field enhancement beneath the tip apex due to delocalized plasmon excitation on a sub-wavelength grating engraved on the tip and nanofocusing of these plasmons. All the simulations of electromagnetic wave scattering on the nanoantenna are based on the finite difference time domain method. We have compared the force exerted on a 2 nm quantum dot nanoparticle of zinc sulphide with two plasmonic optical tweezers: a bare tip and a corrugated tip. In order to better use the concept of a plasmonic optical tweezer, the geometry of this system should be optimized. The geometrical parameters involved in the intensity distribution and consequently the force are the grating period, duty cycle, and the distance from the last grating to the top of the cone. By applying circular grating to the conical plasmonic tweezer made of gold, more force has been applied to the nanoparticle.