Heterogeneous small molecule interactions on surfaces probed with ambient pressure X-ray photoelectron spectroscopy

Newberg, John T.In recent years there has been a significant drive in the surface science to investigate heterogeneous processes under realistic conditions. In this dissertation the quantification and analysis of heterogeneous systems were explored by a variety of techniques to elucidate complex electronic and chemical properties of surfaces in the presence of fundamental gases. In particular, photoelectron spectroscopy operated under ambient pressures was employed to assess chemical reactions and phase transitions of model and applied surfaces. Specifically, this dissertation will focus on the impact of adsorption of water and oxygen on interfacial compositions of salt and metal oxide surfaces. First the extremely hydroscopic system of zinc bromide was investigated as a function of relative humidity with high pressure photoelectron spectroscopy. Advanced analysis of isothermal water uptake yielded results which quantified the energetics of adsorption. Innovative assessment of surface composition with lab-based photoelectron spectroscopy produced findings previously limited to synchrotron-based techniques. Second, the effects of water adsorption upon epitaxial metal oxide films structural relaxation through hydroxylation were investigated. Evidence based on experimental and theoretical observations suggest that various mechanisms of water dissociation may exist between manganese and nickel oxide films but also that the adsorption of water dimers at higher pressures significantly alters the reaction mechanism, promoting further hydroxylation events. Lastly, the photocatalytic properties of manganese oxides were explored under reaction conditions with exposure to light, water, and oxygen gases. Insights were made into the mechanisms of photo reactions with carbonaceous species with implications in photocatalysis. Overall this dissertation strives to highlight the analysis of complex heterogeneous systems with surface sensitive techniques focusing on in-operando conditions that are of broad interest to the surface science community and to provide enhanced understanding of important gas adsorption processes.University of Delaware, Department of Chemistry and BiochemistryPh.D