Understanding the Origin of a Second Mobility Reversal in Optoelectrically Powered Metallo-Dielectric Janus Particles

TL;DR

This study uncovers a second mobility reversal in optoelectrically-driven Janus particles caused by substrate asymmetry and self-shading effects, supported by experiments and simulations.

Contribution

It reveals a novel second mobility reversal mechanism in optoelectronic Janus particles due to substrate asymmetry and localized photoconductivity effects.

Findings

Second mobility reversal observed under optoelectronic driving.

Reversal linked to substrate asymmetry and self-shading effects.

Numerical simulations support the proposed mechanism.

Abstract

While previous studies indicated the mobility reversal of an electrically-powered metallo-dielectric Janus particle (JP) with increasing frequency, here we report an intriguing second mobility reversal observed in optoelectronically-driven JPs. In contrast to the commonly used setup with parallel ITO-coated glass substrates to induce a uniform electric field orthogonal to the velocity direction, this setup incorporates a thin photoconductive layer deposited on the bottom ITO-coated glass substrate. We have found that the reversal is associated with the asymmetry of the bottom substrate's photoconductivity, localized underneath the JP, resulting from the self-shading effect of the metallic hemisphere under top optical illumination. Numerous control tests, including optical illumination from the bottom, along with numerical simulations, support this hypothesized mechanism