Dr. Delphine Coursault, Dr. Tiansong Deng, Dr. Yuval Yifat, John Parker, Nolan Shepherd, Emmanuel Valenton, Carolina Yu
Research QuestionsAre plasmonic excitations useful for coherent information transport in nano-photonic circuits?
Can new materials be created with only optical fields and electrodynamic interactions (i.e. no chemical bonds)?
How does one engineer coherence into such synthetic photonic materials; coherence by design?
We have worked on aspects of these questions since 1995, with initial emphasis on developing new measurement methods [60,65, 74, 79, 91] including the first integration of a femtosecond pulse with an STM where plasmon excitation of the metal film allowed space-time measurement of local electron dynamics [33, 39, 50, 54, 60].
Gold nanoparticle deposit on silica sphere as a chain-like aggregation
Our recent focus has been on the plasmon transport properties of single noble metal nanowires, by simulation and experiment, and optical trapping methods for ordered assembly of nanoparticles and nanowires into active nanoscale plasmonic "devices". Since nano-metallic particles (e.g. spheroids, bipyramids, rods, wires, etc.) are strong light scatters, they are both a challenge to trap (e.g. our work in [146, 148] is the first to demonstrate trapping and orientational control of Ag and Au nanowres in 3D in solution) the scattering also enables another phenomenon termed optical binding. The effect involves the interference of incident and scattered light and thus creates modulated optical fields on the intermediate length scale (d ~ λ) and strong gradients in the near-field of the nanoparticles. These modulated fields, in turn, allow spatially registered trapping of other nanoparticles. We have now been able to create stable 2-D lattices of metal nanoparticles in solution that serve as a template for "co-trapping" of other smaller objects in the regions of large electric fields (and field gradients) in these metal nanoparticle lattices.
As a demonstration we have co-trapped single semiconductor quantum dots into these lattices and by centroid localization  have shown the close spatial correlation of the metal and semiconductor nanoparticles. This largely experimental and simulation effort is complemented by a theory project in which we, in collaboration with Dr. Stephen Gray (ANL/CNM) have developed both semi-classical and quantum mechanical descriptions of coupled plasmon-exciton systems. In this work we have shown how the simple and fast semiclassical treatment, a coupled oscillator-2 level Q-dot system, needs to be modified to properly account for bilinear coupling of exciton and plasmon as embodied in the enhanced radiative rate, strong dissipation into the plasmon and the creation of novel coherent states of the strongly coupled system.
Darkfield image (false color) of optically trapped gold nanoparticles deposited on a glass surface.