Experimental demonstration of new optical properties in hybrid nanostructures




Hartsfield, Thomas Murray

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In this dissertation, I present experimental investigation of the optical properties of nanoscale systems composed of both metallic and semiconductor components. Metallic nanostructures may act as resonant cavities for conduction electrons, allowing drastic electromagnetic field enhancement and the concentration of these surface plasmon field modes into tiny volumes. Semiconductor quantum dot emitters demonstrate desirable and broadly tunable optical properties due to the quantized nature of their internal electron states. When paired together, the absorption, emission, optical gain, and internal energy decay pathways of the quantum dot as well as the scattering of the cavity may be strongly modified. This work focuses on the optical properties of two such model hybrid nanostructure systems. Of the many studies of plasmonic cavities, relatively few investigate the influence of a quantum dot on the scattering of the plasmonic cavity itself. The main experimental challenge lies in the difficulty of placing an absorber or emitter at the desired position: the very virtue of the small mode volume of a plasmonic cavity demands precise spatial emitter placement. We will study the simplest plasmonic cavity, a single metal nanoparticle and a single quantum dot. We assembled a hybrid nanostructure using a nanomanipulation “nano-golfing” technique and demonstrated for the first time that the state of a single quantum dot can resonantly control the scattering of a vastly larger plasmonic cavity, manifested as a Fano resonance. A device of this design could potentially be used as a photon source capable of outputting photons of classical or quantum statistics on demand.

We then turn to the optical properties of the emitter element of a hybrid nanostructure. We measured the ability of an atomically smooth Ag film to influence the optical properties of a quantum dot. This novel system has been shown to produce more uniform emitter-plasmon coupling and a greater product of excitation and radiative decay rates than possible with traditional systems relying upon rough metal films. Applications utilizing coupling between metallic films and quantum emitters could see benefit from high quality atomically smooth films as demonstrated by our studies.



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