| Comparative studies by ellipsometry of the oxidation of the Be(0001) and Ni(111) surfaces under ultra-high vacuum conditions in the temperature range 30-600(DEGREES)C have been made in conjunction with Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). The initial stages of oxygen adsorption and oxide formation, the stability of the oxide surfaces and the long term growth of the oxide were examined.; The basic principles of AES, LEED and ellipsometry with a rotating analyzer are discussed. Models for the optical properties of adsorbates, very thin films, and heterogeneous layers are intro- duced and applied to experimental results on clean surfaces and on surfaces exposed to oxygen.; On Be(0001), a temperature dependent initial decrease in the ellipsometric parameter (psi) is taken to indicate incorporation of oxygen into the beryllium surface. It is proposed that at the minimum in (psi), the surface consists of islands of BeO in an electron depleted Be layer; an effective medium approximation, assuming free electron behavior for Be, can describe the experimental results. No oxygen incorporation is observed on Ni(111) at temperatures below 300(DEGREES)C. Above this temperature, dramatic changes in the ellipsometric para- meters suggest the incorporation of oxygen into the nickel surface. The order-disorder transition in the p(2 x 2)-O overlayer on Ni(111) does not produce measurable changes in the ellipsometric parameters.; Both BeO(0001) and NiO(111) are polar surfaces; the oxide structures consist of alternating planes parallel to these surfaces containing all metal ions or all oxygen ions. The ideal polar oxide surfaces are found to be unstable. After oxide coalescence on Be(0001), p(2 x 2)-BeO and (SQRT.(3) x SQRT.(3) ) R30(DEGREES)-BeO LEED patterns are observed which may arise from ordered surface charges which compensate the bulk polarization of the BeO. Below 200(DEGREES)C, NiO(111) is observed to grow and coalesce on the Ni(111) surface. Above this temperature, the lower energy NiO(100) surface is seen instead. NiO(100) is not observed to coalesce on Ni(111) but rather thickens as large islands.; The long term ((TURN)100,000 L) oxidation of Be(0001) is examined. An oxide layer less than 10 (ANGSTROM) thick passivates the surface at temper- atures up to 350(DEGREES)C. Above this temperature, the oxide growth is temperature dependent. The data can be fit with either logarithmic or parabolic growth laws. |
