Yu, Hui2006-07-282006-07-2819981998http://hdl.handle.net/10012/349A multi-technique portable spectrometer for electron energy loss spectroscopy (EELS) has been developed to study surface reactions and adsorption properties induced by low-energy electron and ion irradiation on two popular model surfaces in surface science: Cu(100) and Si(111)7x7. Both vibrational EELS spectra at high resolution and electronic EELS spectra over an extended energy range have been obtained. Together with other surface analysis techniques, including temperature-programmed desorption mass spectrometry, low-energy electron diffraction and Auger electron spectrometry, the present work examined some of the intriguing aspects of surface processes induced by low energy electron and ion irradiation. The surface interactions of CO with clean, oxygen-precovered and carbon-precovered surfaces of Cu(100) were investigated. In particular, we observed anomalous adsorption of "stabilized" CO species on Cu(100) above room temperature, which was produced in-situ by low-energy electron irradiation of CO/Cu(100) at 120 K or by low-energy ion irradiation of Cu(100) in CO or with pre-exposure of O2 in ethylene at room temperature. The stretching frequency of the "stabilized" CO was found to be either red- or blue-shifted from its nominal (low-temperature adsorption) position, depending on the nearby-coadsorbed species. We proposed a direct-interaction bonding model involving a "titled" CO molecule on an atop site semi-bridge bonded to an O or C atom in a four-fold hollow site. On a c(2x2)N/Cu(100) surface produced by low-energy ion irradiation in N2, we demonstrated the co-existence of embedded nitrogen and surface-bonded nitrogen. Furthermore, we also studied the reactions of ethylene ions with oxygen pre-covered and nitrogen pre-covered Cu(100) surfaces. Along with various hydrocarbon species, CO and CN species were found to adsorb on these surfaces, respectively, at room temperature. On the Si(111)7x7 surface, we studied the effects of surface contamination by ambient gas and carbon on the adsorption of oxygen and water. It was found that the presence of a high level of surface carbon could poison the 7x7 surface, reducing further adsorption by water and hydrocarbons but not by oxygen, whereby in the latter case the nature of oxygen adsorption appeared not to be sensitive to the coadsorbed species. We also investigated the formation of silicon dioxide and silicon carbide layers on Si(111)7x7 generate by both thermal deposition and ion-assisted deposition by electronic EELS and Auger electron spectroscopy. This study showed that a higher efficiency in producing surface carbon could be obtained by using ion-assisted deposition than by the thermal deposition method. However, a high concentration of carbon deposited on the surface by ion irradiation led to the formation of graphite, which in turn prevented carbon diffusion into the bulk. In both the Cu(100) and Si(111)7x7 studies, coadsorbates (contaminants) were found to play an important role on the adsorption and subsequent chemical processes of other common adsorbates.. These studies further demonstrate the enormous potential of using low-energy electron or ion irradiation for surface reaction activation and the effectiveness of the electron energy loss techniques for probing these fascinating phenomena.application/pdf2801664 bytesapplication/pdfenCopyright: 1998, Yu, Hui. All rights reserved.Harvested from Collections CanadaDoctoral Thesis