Switchable optical trapping of Mie-resonant phase-change nanoparticles

TL;DR

This paper introduces a switchable optical trapping method using phase-change nanoparticles of VO₂, enabling reversible attraction or repulsion by inducing phase transitions that alter Mie resonances, with potential applications in optical manipulation technologies.

Contribution

The study demonstrates a novel, reversible optical trapping mechanism utilizing phase-change VO₂ nanoparticles that can switch between attractive and repulsive forces through controlled phase transitions.

Findings

Nanoparticle size determines attraction or repulsion behavior.

Phase transition of VO₂ switches optical forces in a specific size range.

Reversible switching enables dynamic control of nanoparticle manipulation.

Abstract

Optical tweezers revolutionized the manipulation of nanoscale objects. Typically, tunable manipulations of optical tweezers rely on adjusting either the trapping laser beams or the optical environment surrounding the nanoparticles. We present a novel approach to achieve tunable and switchable trapping using nanoparticles made of a phase-change material (vanadium dioxide or VO$_2$). By varying the intensity of the trapping beam, we induce transitions of the VO$_2$ between monoclinic and rutile phases. Depending on the nanoparticles' sizes, they exhibit one of three behaviours: small nanoparticles (in our settings, radius $<0.12$ wavelength $\lambda$) remain always attracted by the laser beam in both material phases, large nanoparticles ($>0.22 \lambda$) remain always repelled. However, within the size range of $0.12$-$0.22 \lambda$, the phase transition of the VO$_2$ switches optical forces between attractive and repulsive, thereby pulling/pushing them towards/away from the beam centre. The effect is reversible, allowing the same particle to be attracted and repelled repeatedly. The phenomenon is governed by Mie resonances supported by the nanoparticle and their alterations during the phase transition of the VO$_2$. This work provides an alternative solution for dynamic optical tweezers and paves a way to new possibilities, including optical sorting, light-driven optomechanics and single-molecule biophysics.