Low-power photothermal probing of single plasmonic nanostructures with nanomechanical string resonators

We demonstrate the direct photothermal probing and mapping of single plasmonic nanostructures via the temperature induced detuning of nanomechanical string resonators. Single Au nanoslits are illuminated with a low-power polarized focused laser beam ({\lambda} = 633 nm). Polarization dependent heat generation in gold nanoslits is then imaged with high sensitivity. A sensitivity of -4.1 ppm/nW with respect to the illuminated light (beam diameter 5.0pm0.8 {\mu}m) is determined for a single nanoslit (1 {\mu}m long and 53 nm wide), which equals to a total light absorption of 16%. This results in a heating of 0.5 K for an illuminance of 8 nW/{\mu}m2. Our results show that nanomechanical resonators are a unique and robust analysis tool for the low-power investigation of thermoplasmonic effects in plasmonic hot spots.