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Permanent link (DOI): https://doi.org/10.7939/R3WP9TF9B

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Surface modification of group 14 nanocrystals Open Access

Descriptions

Other title
Subject/Keyword
semiconductor nanocrystals
photoluminescence
hydrosilylation
X-ray absorption spectroscopy
surface chemistry
quantum confinement
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Kelly, Joel Alexander
Supervisor and department
Veinot, Jonathan (Chemistry)
Examining committee member and department
Mar, Arthur (Chemistry)
Veinot, Jonathan (Chemistry)
Hegmann, Frank (Physics)
Rivard, Eric (Chemistry)
McCreery, Richard (Chemistry)
Swihart, Mark (University of Buffalo)
Department
Department of Chemistry
Specialization

Date accepted
2012-05-31T12:49:52Z
Graduation date
2012-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Group 14 semiconductor nanocrystals exhibit size-dependent optoelectronic properties through the influence of quantum size effects, notably intense photoluminescence (PL). A crucial step toward the realization of their technological potential is the development of effective methods to control the surface chemistry of freestanding nanocrystals. This thesis describes five investigations with this central goal in mind, based on silicon (Si) and silicon-germanium alloy (SixGe1-x) nanocrystals obtained from hydrogen silsesquioxane (HSQ). These composite materials were etched using hydrofluoric acid (HF), to yield freestanding hydride-terminated nanocrystals that undergo a hydrosilylation reaction with terminal olefins, with thermal or near-UV initiation. This reaction produced well-dispersed nanocrystals with increased stability against oxidation, which degrades their PL. The use of near-UV initiation was studied in detail, based on its compatibility with a wide range of olefins and the observation of unique reactivity unseen for hydrosilylation of molecular species. This reactivity of Si nanocrystals was size-dependent, consistent with an exciton-mediated mechanism previously proposed. This observation was explored through separation of a mixture of sizes based on their hydrosilylation reactivity. Exciton-mediated reactivity was also observed in the HF etching of oxide-embedded Si nanocrystal composites. The PL from these materials could be conveniently controlled by irradiating the etching solution, presenting a strategy for controlling the nanocrystal size and polydispersity; however, defect-containing nanocrystals were suggested to be inactive in this etching pathway. The origin of luminescence from Si nanocrystals functionalized using near-UV hydrosilylation was demonstrated to arise from quantum confinement effects using X-ray absorption spectroscopy. These results confirm that the alkyl grafting does not appreciably alter the emission pathway. Oxidation caused by ambient exposure reduced the ensemble PL quantum yield and shift the emission maximum. The morphology of nanocrystals obtained from the co-reaction of HSQ and GeI2 solubilized with trialkylphosphines was evaluated spectroscopically and microscopically to be a heterogeneous mixture of Si- and Ge-rich nanocrystals. The trialkylphosphine used to facilitate GeI2 co-precipitation influences nanocrystal nucleation and growth processes. Indirect evidence was presented for the involvement of Ge in the emission pathway.
Language
English
DOI
doi:10.7939/R3WP9TF9B
Rights
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
Kelly, J.A. and Veinot, J.G.C. (2010) ACS Nano, 4 (8), 4645-4656.

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