Surface studies of the structural, electronic and chemical properties of selected functional material systems

The structural, electronic and chemical properties of thin films and solid surfaces have long attracted interest, both from a fundamental scientific standpoint, and from the strategic implications, a knowledge of such factors has, in a range of applied fields ranging from electronic devices, to catalysis and nanotechnology. In this context, this thesis explores surface properties on the atomic scale within a range of functional material systems. Variable temperature scanning tunnelling microscopy (VT-STM) studies of the oxidation of Si(111)7x7 surfaces, and the deposition of Au on the ultrathin silicon oxide films so formed, have been carried in situ under vacuum conditions. The extent of oxidation as a function of reaction conditions is further elucidated. STM observations indicate that gold grows as 3-D islands on the silicon oxide surface. Annealing of the Au deposited surface allows the gold particles to migrate onto step edges areas and undergo agglomeration. Prolonged annealing of the Au/SiO_2/Si system brings about the Au-assisted decomposition of the silicon oxide layer, resulting in void formation and the migration of Au to the underlying Si substrate. Similar experimental methods were used to investigate growth of ultrathin layers CaF_2 on Si(111)7x7. Two distinct surface phases were formed, depending on the growth flux involved. The deposition of Pt and Pd onto CaF_2/Si surfaces was performed and both metals were found to grow as 3-D islands. Annealing studies of the Pd-deposited surface showed that the tendency for agglomeration depended sensitively on surface coverage, and 1-D metallic 'lines' were formed at step edges under certain circumstances. Needle sensor non-contact atomic force microscopy was employed to study alumina (0001) surfaces under ultra-high vacuum following different surface treatments. High quality alumina surfaces were obtained, allowing atomic resolution in this type of system to be obtained, using the AFM probe employed, and the mechanism of atomic imaging of the (#sq root#31 x #sq root#31) R#+-#9 deg reconstruction is discussed. The electronic properties of thin-film diamond have been studied, with particular reference to the ultra-violet quantum photoyield (QPY). The results highlighted the dependence of the QPY on the diamond surface composition, with particular correlation with the concentration of oxygen. The observations are explained in terms of the electron affinity of the diamond surface, and its variation with surface composition. (author)SIGLEAvailable from British Library Document Supply Centre- DSC:DN063524 / BLDSC - British Library Document Supply CentreGBUnited Kingdo