Light Manipulation with Plasmonic Structures using Phase Change Materials

Over the past decade intensive research has focused on the use of plasmonic structures and metamaterials for the control of electromagnetic radiation. Response of such structures is highly dependent on factors set during fabrication, such as the combination of materials used and as well as their structural dimensions. Despite having many promising optoelectronic applications, the inability to tune the optical response of such structures post fabrication presents serious limitations. To overcome this, we present tunable plasmonic elements formed of plasmonic nanostructures on a thin film of vanadium dioxide (VO 2 ), a phase change material. VO 2 is an attractive option as a phase change material due to its large, reversible transition from a semiconducting to a metallic phase at a critical temperature of 68°C, close to room temperature. While much research on VO 2 is centred on the large changes in the optical properties occurring in the NIR spectral range (above 1 μώ) upon the phase transition, in this work we focus on the changes in the dielectric function of VO 2 in the visible spectral range. In particular, we experimentally and numerically investigate the possibility to use the phase change of VO2 to dynamically tune the plasmonic properties of noble metal nanostructures as well as to manipulate the emission properties of quantum emitters near plasmonic nanostructures. We observe a drastic change in the plasmonic properties of gold nanorods arrays fabricated on a thin layer of VO 2 as the phase transition from the semiconducting to metallic phase of VO 2 is thermally triggered. Upon phase transition, a >50% decrease in scattering in the red spectral region, especially around 650 nm, was detected in dark field scattering experiments (Figure 1a). Moreover, our spectrally and time resolved measurements reveal that the emission properties of quantum dots (CdSeS/ZnS) in the vicinity of the gold nanorod arrays can be modified through the thermal phase change of the underlying thin layer of VO 2 (Figure 1b). When VO 2 is in its semiconducting phase the photoluminescence (PL) of QDs on the nanorods array is quenched compared to the PL of QDs on the same VO 2 thin film but off the array. In contrast, we observe an enhanced light emission of QDs on the array when the VO 2 layer is in its thermally actuated metallic phase. Additionally, the main PL emission peaks of QDs on the nanorod arrays as well as off the arrays red shift by 15 nm, as an effect of heating. The experimental results are accompanied by supporting FDTD simulations.