Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

MVS Chandrashekhar

Abstract

Optical computing has been proposed for high performance applications owing to light's high frequency and noise tolerance. However, the diffraction limit of light prevents the shrinking of optical components to dimensions significantly smaller than the wavelength of light, typically µm's, compared to nm's for electronic devices.

However, by adopting a plasmonic approach, which exploits near field electromagnetic effects at a conductor/dielectric interface, significant shrinkage of the electromagnetic field of light can been achieved, by as much as 1000x, potentially enabling practical nano-photonics. Though significant wavelength shrinkage is possible using surface plasmon polariton (SPP), fundamental carrier scattering process in metals, intra-band scattering, prohibits the realization of a plasmonic chip. The key challenge here is integrating the plasmonic circuitry with the electrical circuitry to realize monolithically integrated plasmonic light emitters, waveguides and detectors, powered simply by a battery. To do this, the guided plasmonic wave must be converted to an e-h pair in the same material. It has been theorized that graphene is the only material that can do this.

Graphene's plasmonic advantage arises primarily from its linear Dirac electronic dispersion. It has been shown theoretically that this allows it to support transverse electric (TE) modes, helpful for coherent SPP formation, detection and propagation, not present in usual 2D systems with parabolic dispersion.

In this thesis we propose epitaxial graphene (EG) grown on SiC, a revolutionary carbon nanomaterial for SPP guiding, leading dramatic improvements over traditional SPP metal waveguides, with shrinkages as large as 300x, and propagation lengths as long as ~200 wavelengths (theoretically predicted) for novel plasmonic applications. A detailed growth study was performed to produce high quality EG, and the growth mechanism was investigated. Evidence of SPP formation at the EG/SiC interface through FTIR was shown, by exploiting SiC's dielectric singularities in the restrahlen band (8-10 µm) regime, consistent with both theory and experiments. As an application, SPP was exploited in molecular gas sensing applications for emissions controls, with the modeled/fitted extraction of surface impurity concentration, carrier transport parameters, and percentage charge transfer/molecule to the EG layer.. This SPP resonance was tuned by fabricating micro-ribbons on EG, and was interpreted through a solution of Maxwell's equations . Finally, the roadmap for a plasmonic chip using EG on SiC has been established by theoretical prediction of electron-hole pair coupling, generated from SPP which finds application for next generation optical computing. The limits on these predictions are discussed in light of EG/SiC's non-intrinsic nature in ambient conditions.

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