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Type of Document	Dissertation
Author	Boer, Elizabeth A.
Author's Email Address	eboer AT alumni.caltech.edu
URN	etd-01132002-032219
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-01132002-032219
Title	Synthesis, passivation and charging of silicon nanocrystals
Degree	PhD
Option	Applied Physics
Advisory Committee	Advisor Name Title Harry Atwater Committee Member Kerry Vahala Committee Member Richard Flagan Committee Member Stephen Quake Committee Member
Keywords	quantum dots nanoparticle manipulation nanoparticles
Date of Defense	2001-02-09
Availability	unrestricted
Abstract Silicon nanocrystals are intriguing from both a fundamental and an applied physics point of view. The efficient room temperature luminescence exhibited by Si nanocrystals (as compared to bulk silicon) and the apparent size-dependent bandgap of Si nanocrystals are two incompletely explained phenomena. Meanwhile, the applied physicist may take advantage of the optical and electronic properties of small Si structures to build devices not possible with only bulk silicon. In this thesis, nanocrystal samples produced by aerosol techniques were investigated. The aerosol samples were size-classified in the size range of 2-50 nm with a size variation of 15-20%. Conducting tip atomic force microscopy (AFM) was used to manipulate and investigate the samples' charging characteristics. The AFM was used to inject charge into single Si nanocrystals and to observe the dissipation. The charging characteristics of samples made by ion implantation and annealing were also explored. An atomic force microscope was used to locally inject, detect and quantify the amount and location of charge in SiO2 films containing Si nanocrystals (size 2-6 nm). By comparison with control samples, charge trapping was shown to be due to nanocrystals and not ion implantation-induced defects in these samples. Two models were developed for quantitative charge imaging with an atomic force microscope, one appropriate for non-contact mode and the other for intermittent contact (tapping) mode imaging. From the models, estimates of the best charge sensitivity of an unbiased standard AFM cantilever were found to be on the order of a few electrons. The models were used to estimate the amount of charge injected in the charging experiments: in typical experiments, on the order of 60 electrons were injected in an isolated Si nanoparticle, and a few hundred electrons were injected in SiO2 films containing Si nanocrystals. Finally, for optical studies, nanocrystal passivation with hydrogen and SiO2 were briefly investigated using photoluminescence and X-ray photoelectron spectroscopy.
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