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Hierarchical Semiconductor, Metal and Hybrid Nanostructures and the Study of their Light-Matter Interactions

December 10, 2013 11:00AM to 12:00PM
Presenter 
Anna Lee, University of Toronto
Location 
Building 440, Room A105-106
Type 
Seminar
Series 
NST Nanoscience Seminar
Abstract:
The interdisciplinary work during my Ph.D. and post-doctoral studies (Dept. of Chemistry and Dept. of Electrical Engineering, University of Toronto) explore the optical properties of hierarchical structures composed of nanoscale building blocks ranging from metals to semiconductors and composites, organized through bottom-up design methods.

This talk is comprised of three main research projects for which the common thread is the rational design of nanoscale assembled structures and their interactions with light.

Recent advances in spectrally-tunable solution-processed metal nanoparticles have provided unprecedented control over light at the nanoscale. The plasmonic properties of metal nanoparticles have been explored as optical signal enhancers for applications ranging from sensing to nanoelectronics.

Specifically,

  • (1) by following the dynamic generation of hot-spots in self-assembled chains of gold nanorods (NRs), we have established a direct correlation between ensemble-averaged surface- enhanced Raman scattering (SERS) and extinction properties of these nanoscale chains in a solution state. Experimental results were supported by comprehensive finite-difference time-domain simulations. Building from this,
  • (2) we studied an alternate geometry, namely side-by-side assembled NRs. There is a general misconception that aggregates of metal nanoparticles are more efficient SERS probes than individual nanoparticles, due to the enhancement of the electric field in the interparicle gaps. However, we have shown through theoretical and experimental analyses that this is not the case for side-by-side assembled gold NRs.
  • (3) Progress in colloidal quantum dot photovoltaics offers the potential for low-cost, large-area solar power; however, these devices suffer from poor quantum efficiency in the more weakly-absorbed near infrared portion of the sun’s spectrum.

Hierarchical Semiconductor, Metal and Hybrid Nanostructures and the Study of their Light-Matter InteractionsHere, I will talk about a plasmonic-excitonic solar cell that combines two jointly-tuned solution processed infrared materials. We show through experiment and theory that a plasmonic- excitonic design using gold nanoshells with optimized single-particle scattering-to- absorption cross section ratios leads to a strong enhancement in near-field absorption and resultant photocurrent in the performance-limiting near infrared spectral region. The present work offers guidance towards the establishment of “design rules” for the development of colloidal nanoparticle assembled systems for plasmonic sensing applications