Chemical and Biological Engineering ETDs

Publication Date

7-12-2014

Abstract

Solution synthesis is a common method of generating semiconductor nanocrystals. For solution synthesis, many studies have assumed that the growth rate is diffusion-limited with an unphysically low diffusion constant. In this thesis, a model is developed that considers both diffusion and surface kinetics. The diffusion coefficient of Ge monomers through the solvent, octadecene, at elevated synthesis temperatures is estimated to be on the order of 10-5 to 10-4 cm2/sec, while the mass transfer boundary layer thickness is estimated to be on the order of a few nanometers, similar to the nanocrystal size. These two realistic conditions strongly suggest that the common assumption on diffusion limitation may not be warranted and that surface adsorption and desorption of growth precursors and ligands must govern the nanocrystal growth rate. The modeling incorporates the surface rate coefficients as fitting parameters, where the rate coefficients of organic ligands experimentally measured on Ge (111) surface are used as initial values. It is assumed that Ge monomers adsorb on the nanocrystal surface irreversibly. The modeling results on nanocrystal size as a function of time agree well with the experimental outcome, strongly supporting that the Ge nanocrystal growth rate is governed by the surface kinetics and not by the boundary layer diffusion.

Keywords

Germanium, nanocrystal, kinetics, Model, diffusion, boundary layer

Document Type

Thesis

Language

English

Degree Name

Chemical Engineering

Level of Degree

Masters

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Han, Sang

Second Committee Member

Petsev, Dimiter

Third Committee Member

Boyle, Timothy

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