Vanadium oxide is a key sensing material for bolometric photodetection, thanks to its strong temperature dependence of resistivity close to room temperature. Here we demonstrate the photodetection of a stoichiometric vanadium dioxide thin film integrated with silver nanorods. The nanorods convert light into heat, consequently suppressing the resistivity of vanadium dioxide via localised surface plasmon resonance. Incorporation of this thermo-plasmonic effect into bolometric photodetection allows for wavelength and polarisation sensitivity. This work opens the path to a broad family of photodetection functionalities for vanadium dioxide-based microbolometers.

Analytical modelling of hysteresis is used to provide crucial prediction and insight for phase transitions in materials. Here we present a modified Maxwell Garnett model for analysing electromagnetic hysteresis. The model uses an asymmetric effective medium approximation to describe intermediate states in the phase change, establishing a link between effective medium and hysteresis analysis. Numerical calculation was performed on an example material, vanadium dioxide, for quantitative demonstration and future experimental verification. The model is easy to use, requires very few input parameters, and provides a phenomenological approach to describing electromagnetic hysteresis in various phase change materials.

Nanophotonic particle manipulation exploits unique light shaping capabilities of nanophotonic devices to trap, guide, rotate and propel particles in microfluidic channels. Recent introduction of metalens into microfluidics research demonstrates the new capability of using nanophotonics devices for far-field optical manipulation. In this work we demonstrate, via numerical simulation, the first tunable metalens tweezers that function under dual-beam illumination. The phase profile of the metalens is modulated by controlling the relative strength and phase of the two coherent incident light beams. As a result, the metalens creates a thin sheet of focus inside a microchannel. Changes to the illumination condition allow the focus to be swept across the microchannel, thereby producing a controllable and reconfigurable path for particle transport. Particle routing in a Y-branch junction, for both nano- and microparticles, is evaluated as an example functionality for the tunable metalens tweezers. This work shows that tunable far-field particle manipulation can be achieved using near-field nano-engineering and coherent control, opening a new way for the integration of nanophotonics and microfluidics.

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Thermo-plasmonic engineering at the nanoscale can control material properties at the macroscopic scale. We demonstrate utilising plasmonic resonance to tune the effective phase transition temperature and electrical conductivity of vanadium oxide thin films.