Resonant enhancement of the thermoreflectance response of silicon nanodisks

Optical thermometry techniques enabled by a material's thermoreflectance response are widely employed for thermal imaging of microelectronic devices and measurements of thermal transport in nanomaterials. Traditional thermoreflectance transducers are comprised of metal thin-films and exhibit relatively poor temperature sensitivity and limited tunability. The ability to exploit optical resonance in high-index dielectric materials to enhance the thermoreflectance response is promising but remains underexplored. In this work, we demonstrate quantitative thermometry using a nanophotonic transducer comprised of a single silicon nanodisk. We fabricated the nanodisk from a silicon-on-insulator wafer using electron beam lithography and calibrated its thermoreflectance response with a tightly focused laser beam of 532 nm wavelength. For a 406 nm disk diameter, we achieve a thermoreflectance coefficient of −2.76 × 10−3 K−1, which is 10 times higher than what can be achieved with a traditional metal transducer. Supporting calculations reveal that the observed thermoreflectance enhancement is due to the resonant excitation of a magnetic dipole-type mode in the disk. Enabled by the improved thermoreflectance response, we demonstrate a temperature resolution of 153 μK in a 7.8 mHz bandwidth at room-temperature. Ultimately, improving the temperature- and spatiotemporal-resolution of the thermoreflectance technique could unlock measurements that improve our fundamental understanding of energy transport and conversion in emerging nanomaterials and optoelectronic devices.