Charge Redistribution And Electronic Behaviour Of Gold-coper Alloys: Bulk And Surface Studies

The electronic and physical properties of noble metals and their alloys have been the focus of research for many years. They are considered prototypes for the investigation of full d-band interactions and Friedel charge screening.;We have studied a series of bulk Au-Cu alloys, with varying compositions and ordering, in order to determine the nature and amount of charge transfer between the two components. We also examine the validity of two models; charge compensation and d-d repulsion. To probe the electronic behaviour upon alloying, we employ two techniques, namely photoemission and X-ray absorption. From photoemission, we find unique behaviour in the alloy valence band, indicating separate contribution from each component and distinctive movement showing the validity of the d-d repulsion model. Semi-quantitative results for the amount of d charge transfer (independently determined by X-ray absorption experiments) and conduction charge transfer from Mossbauer isomer shifts, clearly show that Au loses d charge but is overcompensated by a gain of s-p charge giving the Au site a small overall gain of charge in line with electroneutrality and electronegativity arguments. It was found that the amount of charge transfer is directly related to the local configuration of the alloy (number of Cu neighbours around the Au site) and that the valence band behaviour is dependent on the dilution of Au-Au interactions (and also Cu-Cu interactions).;Also of more recent importance, is the study of model bimetallic catalysts, such as Au on Ru(001) and Cu on Ru(001). We have focussed not only on these bimetallic systems but also on a trimetallic system, Au-Cu on Ru(001). Using the results of the bulk study, indicating unique behaviour upon alloying especially in the valence band, we have found that co-deposition of these components, at room temperature and in the monolayer regime, leads to alloy formation which is not observable in the bulk. We propose a mechanism based on the heats of adsorption of the components, the heat of formation of Au-Cu alloys, and the role of the substrate in reducing the activation barrier