Ellipsometry of clean surfaces, submonolayer and monolayer films

Abstract

The geometric and electronic structure of the surface region of a crystal is often different from the bulk structure and therefore the optical properties differ in principle also. Theories for the optical properties of (sub)monolayer films are compared, with special attention to anisotropic layers. The review of experimental studies in ultra high vacuum systems mostly concerns ellipsometric measurements of chemisorption of oxygen on metal surfaces (Ag, Cu, Ni). With the combination ellipsometry-AES-LEED linear relationships have been observed between the change in A and the coverage of oxygen chemisorbed on Ag(llO), Cu(lOO), Cu(ll1) and Cn(ll0). At room temperature the 6A values per oxygen atom on the different Cu planes are equal, and are larger than the 6A value per atom taken up in a later stage of oxidation. For the anisotropic Cu(l10) plane the SA and Sli, values per adsorbed oxygen atom depend on the crystal temperature and the azimuthal orientation of the plane of incidence of the light beam. In order to explain the observed changes in A and I$, models are discussed in which changes in the substrate, caused by chemisorption, are taken into account.

Oxygen electrosorption on copper single crystal electrodes in sodium hydroxide solution

“…These samples show the lowest n and the highest k values. This forms further support for the opinion of Albers et al [12] and Habraken et al [13], that "defect-free' surfaces show a tendency to lower n and higher k values. No systematic differences were found between the values for the different single crystal planes.…”

The adsorption and incorporation of oxygen on Cu(100) and its reaction with carbon monoxide; comparison with Cu(111) and Cu(110)

“…and remains constant upon further oxygen exposure. The ellipsometric data and their plane-specificity will be discussed in more detail in a forthcoming paper [30].…”

The interaction of oxygen with Ni(100) and the reduction of the surface oxide by hydrogen

“…Auger electron spectroscopy and LEED have been used to correlate the observed ellipsometric signals with surface coverages. A more detailed interpretation of ellipsometric data in the (sub)monolayer region is difficult as will be shown in a future publication [17].…”