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Title: Investigation of adsorbates on metal single crystal electrodes
Author: Antonatos, Nikolaos
ISNI:       0000 0004 7656 9025
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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The aim of this thesis is to provide a detailed investigation of the behaviour of several adsorbates on noble metal single crystal electrodes. The effect of these adsorbates on structural changes of the underlying substrate is discussed as well. For this research surface X-ray diffraction (SXRD) and electrochemical techniques have been mainly employed. The study of the atomic structure of silicon and silver atoms forming the (4 x 4) silicene structure on Ag(111) single crystal in room temperature revealed a honeycomb structure with a buckling of the Si atoms of 0.76 Å. Furthermore, the buckling of silicene produces a distortion effect upon the top two Ag layers of the crystal which is dependent of the temperature. Additional investigations were carried out to examine the orientation of acetonitrile (CH3CN) on the Cu(111) and Ag(111) single crystal electrodes in perchloric acid via in situ SXRD techniques. This was studied as a function of acetonitrile concentration and electrochemical potential to determine how these factors affect the adsorbate structure at the interface. The results indicate acetonitrile orients perpendicular to the Cu(111) surface with the CN group of the molecule bonding with the surface atoms. It was further shown that due to acetonitrile, copper atoms dissolute from the crystal surface and are redeposited in a different orientation to the substrate. At high acetonitrile concentrations, the molecule decomposes to the -CH3 and -C=N groups where the latter complexes with the copper atoms. On the other hand, acetonitrile orients parallel to the Ag(111) surface interacting weakly with the top silver atoms via the p orbital of the nitrile group. Therefore, it is established that the impact of acetonitrile on Cu(111) is much more prominent than on Ag(111). The influence of acetonitrile is further examined on the under-potential deposition (UPD) of copper on Au(111) in sulphuric acid over a wide range of acetonitrile concentrations by cyclic voltammetry and chronoamperometry. The influence of acetonitrile on the resulting copper structure and coverage is discussed based on the electrochemical results and in situ SXRD. The presence of the organic molecule is found to affect the deposition behaviour, strongly enhance the resulting copper coverage deposited on Au(111) and alter the final copper structure.
Supervisor: Grunder, Yvonne ; Lucas, Christopher Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral