Degree Type

Dissertation

Date of Award

2003

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Patricia A. Thiel

Abstract

The work in this dissertation presents studies of three distinct areas of interest in the field of quasicrystals: bulk structure, transport properties, and electronic structure. First, we describe the results of a study which explored the fundamental interactions between the atomic species of the icosahedral Al-Pd-Mn quasicrystal. This study was done using laser vaporization to create gas-phase metal clusters, which were then ionized and analyzed using time-of-flight mass spectrometry. Both the kinetic and thermodynamic stabilities of the clusters were probed.;Second, we report our investigations of the bulk thermal transport properties of a decagonal Al-Ni-Co quasicrystal in the temperature range 373K--873K. The properties of a sample oriented along the periodic, aperiodic, and 45° axes were measured. A high degree of anisotropy was observed between the aperiodic and periodic directions. The results of the 45° off-axis data were compared with theoretically predicted values. Transport behavior is described in terms of charge carriers and the mean-free time between carrier collisions. It is concluded that the mean-free time is much longer in the periodic direction than in the aperiodic direction, producing the observed anisotropy in thermal transport.;The third study presents a detailed analysis of the sputter-induced phase transformation which occurs on the 5-fold surface of an icosahedral Al-Cu-Fe quasicrystal. Reflection high-energy electron diffraction, x-ray photoemission spectroscopy, and ultra-violet photoemission spectroscopy data were collected as a function of annealing temperature and were used to probe surface structure, surface composition, and electronic structure, respectively. The composition and structure of the sputtered surface are consistent with a transformation to the beta-Al-Cu-Fe cubic structure, and shows a sharp metallic cut-off in the spectral intensity of the electronic structure at the Fermi edge. Upon annealing the surface reverts to a quasicrystalline composition and structure. This is correlated with a reduction in spectral intensity at the Fermi level. It is concluded that this is due to the opening of a pseudo-gap in the electronic density of states as the surface reverts from beta-Al-Cu-Fe to quasicrystalline.

DOI

https://doi.org/10.31274/rtd-180813-12042

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Jason A. Barrow

Language

en

Proquest ID

AAI3105065

File Format

application/pdf

File Size

128 pages

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