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Title: Surfaces of the icosahedral Ag-In-Yb quasicrystal : structure, reactivity and thin film growth
Author: Nugent, Peter John
ISNI:       0000 0004 2734 8111
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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Quasicrystals are intermetallic alloys which exhibit long range order but lack periodicity. While, until recently, all stable quasi crystal species discovered are ternary alloys, consisting of 3 ele- mental species, recent studies have developed the binary system i-Cd- Yb, which in turn has led to the inception of a new family of ternary quasicrystals, of which one is i-Ag-In-Yb. This the- sis documents studies performed on the high symmetry surfaces of the i-Ag-In-Yb quasicrystal using a variety of techniques such as STM, LEED, XPS, UPS, MEIS and thin film deposition. The five, three and twofold high symmetry surfaces of i-Ag-In-Yb have been characterised in terms of their atomic structure and composition. All three surfaces produce surfaces that are atomically fiat and composed of a stepped and terraced structure. All three surfaces are found to be formed along atomic planes that intersect the centers of the rhombic triacontahedral (RTH) clusters, the building blocks of this material. By comparing the results from STM, LEED, XPS and MEIS, the structure and composition of the these surfaces are determined to be bulk truncated. Each surface also possesses comparable stabilities. The deposition of Sb on the fivefold surface creates a quasiperiodic overlayer expressing long range order. The thin film grows firstly as a monolayer with Sb atoms forming fivefold features on top of the truncated RTH clusters. It then forms a partial second layer before growing in a disordered manner. The first layer Sb atoms settle in adsorption sites similar to those recorded for the Pb monolayer on the same surface. The second layer of Sb adsorps in sites forming pentagonal features that are T scaled in size in respect to the monolayer features. Depositing C60 on both the clean surface and the clean surface modified by a predeposition of Sb yields a thin film expressing no ordering. Behaviours that are expressed when exposed to oxygen for all three high symmetry surfaces are identical, with each constituent species also behaving in a similaiar manner to each element in its pure form. Upon oxidising the fivefold surface in vacuum, atmospheric conditions, and water, it was found that water is the most effective oxidising agent due to a greater concentration of oxygen.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral