The growth and characterisation of aperiodic copper thin films on the five-fold and two-fold surfaces of the icosahedral Al70Pd21Mn9 quasicrystal

E. Reid, Dennis (2006) The growth and characterisation of aperiodic copper thin films on the five-fold and two-fold surfaces of the icosahedral Al70Pd21Mn9 quasicrystal. PhD thesis, University of Liverpool.

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Abstract

This thesis is the culmination of a sustained period of work at the Surface Science Research Centre of the University of Liverpool, The Davey Laboratory at Penn State University and BL 4.1 at the Daresbury Synchrotron Radiation Facility, and represents the first time a single element quasicrystalline multi-layer thin film has been created on any quasicrystalline surface. An ultrathin film with a periodic interlayer spacing was grown by the deposition of copper atoms on the five-fold surface of the ¿-Al70Pd2iMng quasicrystal. For coverages from 5 to 25 ML, a distinctive quasiperiodic LEED pattern is observed. STM images show that the in-plane structure comprises rows having separations of S' = 4.5 ± 0.2 A and L = 7.3 ± 0.3 A, whose ratio equals r = 1.618... The sequences of such row separations form segments of terms of the Fibonacci sequence, indicating the formation of a pseudomorphic Cu film. LEED measurements performed at 85 K indicate that Cu atoms are organised periodically with a nearest neighbour distance of 2.5 ± 0.1 A along the aperiodically spaced rows. Above 8 ML spontaneous mass transport resulting in island formation has been observed by STM. These observations point to ascending adatoms being responsible for the formation of 3-D features. Flashing the multilayer film to 570 K results in the diffusion of Cu into the bulk and the formation of 5 periodic domains. The electronic structure of the clean and Cu dosed surface was also explored using Soft-XPS. Clean surface data was in good agreement with previous studies. Valence and core level data suggests that Cu dosing in the presence of oxygen leads to a different growth mode of the film. The so called ‘pseudogap’ was also found in Fermi level scans of the clean surface and this feature continued to be observed on the dosed surface at least up to a coverage of 2.6 ±1.0 ML. Finally the two-fold surface of the z-Al7oPd2iMng quasicrystal has been studied using STM, LEED and AES. Two phases are observed: a quasiperiodic phase, in agreement with previous work, and a periodic phase tentatively identified as orthorhombic. Cu deposition on the two-fold surface leads to a multilayer thin film exhibiting a quasiperiodic LEED pattern.

Item Type:	Thesis (PhD)
Depositing User:	Symplectic Admin
Date Deposited:	20 Oct 2023 12:40
Last Modified:	20 Oct 2023 12:56
DOI:	10.17638/03174675
Copyright Statement:	Copyright © and Moral Rights for this thesis and any accompanying data (where applicable) are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge.
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3174675