Abstract:
Hybrid materials structured on the molecular scale hold the promise to realize optical properties that are drastically different from their bulk counterparts. For example, metal-dielectric nanocavities may tightly confine light to small mode volumes resulting in strongly increased local density of states. Placing fluorescing molecules or semiconductor materials in this region enables wide control of radiative processes including absorption and spontaneous emission rates, quantum efficiency, and emission directionality. In this talk, I will describe our recent experiments utilizing a tunable plasmonic platform where emitters are sandwiched in a sub-10-nm gap between colloidally synthesized silver nanocubes and a metal film. Utilizing dye molecules with an intrinsic long lifetime reveals spontaneous emission rate enhancements exceeding a factor of 1,000 while maintaining directional emission and high quantum efficiency [Nature Photon. 8, 835 (2014)]. Incorporating semiconductor quantum dots into the nanocavities enables ultrafast spontaneous emission corresponding to emission rates exceeding 90 GHz [Nat. Commun. 6, 7788 (2015)] as well as an ultrafast and efficient single photon source [Nano Lett., 16, 270 (2016)]. Leveraging higher-order modes of the cavity allows optical processes at multiple energies to be optimized simultaneously which we demonstrate using monolayer MoS₂ [Nano Lett. 15, 3578 (2015)]. Finally, at a surface fill fraction of ~20%, the film-coupled nanocubes behave as spectrally selective perfect absorbers which can be tuned from the visible to the near-infrared [Advanced Materials 27, 7897 (2015)] promising for ultrafast optoelectronics, bio-sensing and renewable energy applications.