Date of Award

2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Materials Science & Engineering

First Advisor

Ritesh Agarwal

Abstract

ENGINEERING PHONON, PHOTON, ELECTRON AND PLASMON INTERACTIONS IN SILICON - METAL NANOCAVITIIES FOR SILICON PHOTONICS AND THERMOPLASMONICS

Daksh Agarwal

Ritesh Agarwal, PhD

Silicon photonics offers a cost effective solution to achieve ultrafast data processing speeds. But due to its indirect bandgap structure, making lasers from silicon is extremely difficult. Thus research has focused on nonlinear Raman processes in silicon as a method to achieve optical gain. Silicon nanowires provide an interesting platform for enhancing these nonlinearities because of their small size, geometry and relevant length scales. In the current work Raman measurements done on silicon nanowires reveal that up to twelvefold enhancement in Stokes scattering intensity and fourfold enhancement in anti Stokes scattering intensity can be attained depending on cavity structure and size, and excitation wavelength. In some cavities Stokes intensity depends on the sixth power of pump intensity, indicating extreme nonlinearity. Numerical calculations, done to understand the mechanism of these results indicate that silicon nanowires confine light to highly intense electric field modes inside the cavity which lead to stimulated Stokes and anti Stokes Raman scattering. Cavity modes can also be tuned to enhance the relative emission of either one of anti Stokes or Stokes photons which could enhance cavity cooling. These results would enable the development of smallest monolithically integratable silicon laser with extremely low lasing threshold and could lead to the development of next generation of high speed and energy efficient processors. The intense electric field inside the nanowire could also be used to enhance the degree of plasmon excitation in metallic nanoparticles. Silicon nanowires coated with a 10 nm thick gold film lead to strong plasmon excitation in gold and high cavity absorption which enable the cavity to heat up to temperatures of 1000K at relatively low pump powers. The cavities also give the ability to measure temperature attained during plasmon excitation and control the plasmon resonance wavelength. Because of the strong heating and plasmonic effects, these cavities show enhanced evolution rates of hydrogen, a crucial industrial building block and a promising fuel, in photoreforming reactions of alcohols.

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