Monday, 16 February, 2015
An Optically Controlled Microscale Elevator Using Plasmonic Janus Particles
S. Nedev, S. Carretero-Palacios, P. Kühler, T. Lohmüller, A. Urban, L. Anderson, and J. Feldmann -
ACS Photonics, doi: 10.1021/ph500371z, published online: 16 February 2015
In this article, we report how Janus particles, composed of a silica sphere with a gold half-shell, can be not only stably trapped by optical tweezers but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upward motion of the particle, while a decrease leads to a downward motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control the distance between the two particles inside the trap. This photonic micron-scale elevator is a promising tool for thermal force studies, remote sensing, and optical and thermal micromanipulation experiments.