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Whispering gallery modes in layered microspheres: mode structure, thermal response, and reactive sensing Open Access


Other title
silicon quantum dots
whispering gallery modes
refractometric sensing
mode structure
thermal stability
Type of item
Degree grantor
University of Alberta
Author or creator
Zhi, Yanyan
Supervisor and department
Meldrum, Al (Department of Physics)
Examining committee member and department
Marsiglio, Frank (Department of Physics)
Currie, Claire (Department of Physics)
Tsui, Ying (Department of Electrical and Computer Engineering)
Heitmann, Johannes (Institut für Angewandte Physik, Technische Universität Bergakademie Freiberg)
DeCorby, Ray (Department of Electrical and Computer Engineering)
Department of Physics

Date accepted
Graduation date
Doctor of Philosophy
Degree level
This thesis focuses on the physics of the whispering gallery modes (WGMs) of silica microspheres coated with a layer of fluorescent silicon quantum dots (Si QDs). The basic theory associated with these structures was explored, and we showed how the important physical parameters such as the quality factor (Q factor), resonance wavelengths, electric field profile, and thermal properties can be straightforwardly calculated. The QD coating plays a major role in controlling each of these key parameters. The QDs also provide a fluorescent source which can couple to the WGMs of the microsphere, avoiding the complexity and fragility associated with coupling via an “evanescent” field. After a thorough discussion of the experimental issues associated with the fabrication and measurement of these structures, we next showed how the cold-cavity modes are related to the WGMs observed in the fluorescence spectrum. Then we examined theoretically the basic properties of the WGMs, their thermal response, and the sensing capabilities associated with these structures. Based on the theory, a microsphere demonstrated extreme stability against local temperature fluctuations. Finally, the refractometric sensor response of the coated microsphere devices was studied. This required the design of different fluidic environments to test the sensor response. The detection limits approached 10^{-5} refractive index units, which appeared to be limited mainly by the wavelength shift resolution of the analysis method and by mechanical drift. Finally, outstanding issues and potential future directions were discussed.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Y. Zhi and A. Meldrum, “Resonance structure of quantum-dot-coated microspheres for microfluidic sensing,” the proceedings of the SPIE, vol. 9288, p. 92880Y, 2014.Y. Zhi and A. Meldrum, “Tuning a microsphere whispering-gallery-mode sensor for extreme thermal stability,” Applied Physics Letters, vol. 105, no. 3, p. 031902, 2014.Y. Zhi, T. Thiessen, and A. Meldrum, “Silicon quantum dot coated microspheres for microfluidic refractive index sensing,” Journal of the Optical Society of America B, vol. 30, pp. 51-56, Jan 2013.Y. Zhi, J. Valenta, and A. Meldrum, “Structure of whispering gallery mode spectrum of microspheres coated with fluorescent silicon quantum dots,” Journal of the Optical Society of America B, vol. 30, pp. 3079-3085, Nov 2013.Y. Zhi, C. Manchee, J. Silverstone, Z. Zhang, and A. Meldrum, “Refractometric sensing with silicon quantum dots coupled to a microsphere,” Plasmonics, vol. 8, no. 1, pp. 71-78, 2013.

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