Spectroscopic considerations on molecular adsorption at the solid/liquid interface

This thesis mainly focuses on the adsorption behaviour of various molecules at the solid/liquid interface. The variation in adsorption kinetics are studied as a function of concentration, pH, applied electrode potential and surrounding environment by the surface sensitive analytical techniques of Reflection Anisotropy Spectroscopy and X-ray Photoelectron Spectroscopy. An electrochemical investigation into the surface reconstructions of Au(110) and their associated RA profiles is undertaken. The spectral profiles of Au(110) in 0.1 M H2SO4/Na2SO4, NaClO4/HClO4 and NaClO4 electrolytes were observed as a function of potential and spectral signatures of the different reconstructions are assigned. The adsorption of adenine and its monophosphate (AMP) on Au(110) was studied using RAS. It is shown that both molecules adsorb in a vertical orientation through sites common to the base through formation of base stacked layers. Application of a phenomenological Lorentzian transition model and rotations about the polarisation direction of the incident light suggest that the molecules align along the [1 0] principal axis of the substrate. Linear simulations show that the orientation of adenine at sub-saturation coverage is the same as that when a monolayer is adsorbed and that adenine does not adsorb on the surface at sufficiently alkaline pH. The attachment of thiolated ss DNA on a functionalised diamond surface and the subsequent detection of hybridisation are discussed. High resolution XPS spectra are used to characterise both the integrity and structure of the organic thin film and its modification to precipitate DNA adsorption. The sensitivity of RAS to the orientation of the alkyl backbone of decanethiol is displayed through alteration to the surrounding environment of the molecule. It is suggested that orientation of the hydrophobic backbone varies as the surrounding environment is changed from ethanol to air and finally to phosphate buffer