Detecting Photothermoelectric Voltages from Surface Plasmon Polariton Excitation in Gold Nanoscale Devices

Thermoelectric properties of nanostructured materials heated under laser illumination can be detected via measurable open-circuit voltages, which can be useful for applications such as photodetection. Large open-circuit photovoltages have been detected in single metal, plasmonically-active structures with nanogaps when the gap is directly illuminated with resonant light, consistent with “hot” carrier generation from plasmon excitation. This effect is particularly evident in thin gold “bowtie” devices because of the strong local plasmon resonance in the nanowire constriction. Direct optical excitation of the nanogap can cause high local heating which can cause nanogap morphology instability. To reduce this temperature rise, metallic gratings are added to the electrode design which can be illuminated to excite propagating plasmons that couple into the junction region without direct excitation by far-field radiation. We will present how the open-circuit voltage of these devices with and without nanogaps varies as a function of incident laser position and discuss how the results of remote excitation of the nanogap via propagating plasmons compare to direct excitation, in the context of "hot" carriers.