Monolayer Of Sulfur Research Articles

Substrate steps/adsorbed layer interaction; selective effect on the possible epitaxial relationships: Case of the S/Cu ∼ (111) system

The interaction between monoatomic steps on a vicinal ∼ (111) copper surface and the adsorbed sulphur monolayer has been investigated by a method involving the existence of two possible structures of the monolayer. The parts of the surface occupied by each structure, which are equal on a perfect (111) crystal plane, and differ on a vicinal surface (selective effect of the steps), have been deduced from LEED intensity measurements. Experiments on a wide range of surfaces have revealed a very strong selective effect of the steps, even for misorientations as small as 4° off the (111) plane. On surfaces with 〈3 2 1〉 steps, only one monolayer structure exists, which appears to fit perfectly the steps. The behaviour of the other surfaces having the same misorientation angle allowed us to devise a model of the step/monolayer interaction, which includes a partial decomposition of a step into the two nearest 〈3 2 1〉 steps (2D “faceting”). A general framework for exploiting experiments of the kind described above, on other adsorption systems, is also outlined.

Theory of photoemission from localized adsorbate levels

A detailed analysis of a recently developed theory of the angle- and energy-resolved photoemission from localized adsorbate levels is presented. The non-plane-wave nature of the final state originating in the repeated scattering of the outgoing wave by the surrounding atoms constitutes the essential feature of this theory. It is shown that the resulting interferences lead to experimentally observable structure in photoemission spectra which is sensitive to the position of the adsorbate relative to the substrate. Emphasis is placed on the emission from simple, atomiclike orbitals since they permit an unambiguous identification of final-state interactions. Sample calculations are performed to illustrate these effects in the case of emission from the adsorbate $2s$ level for a sulfur monolayer on a nickel substrate.

Measurement of ionization cross-sections and backscattering factors for use in quantitative AES

For the extraction of quantitative information from Auger electron spectra two parameters (apart from a number of instrumental parameters) are of utmost importance: the ionization cross-section and the backscattering factor. The determination of these two parameters is discussed. Ionization cross-section values for L- and M-shells have been determined based on existing values for K-shells from the literature. The backscattering factor for Si is calculated as a function of energy of the primary electrons and compared with absolute measurements of this factor using an adsorbed monolayer of sulfur or oxygen on a Si (100) surface.

Adsorption and oxidation of sulphur and of sulphur dioxide at the platinum electrode

Summary The adsorption and oxidation of sulphur and of sulphur dioxide on a smooth platinum electrode have been studied by the potentiodynamic method. The charges consumed in the anodic oxidation of adsorbed sulphur as well as of adsorbed sulphur dioxide are considerably higher than those required for the oxidation of a monolayer of sulphur or of sulphur dioxide, respectively. In the course of the anodic oxidation of the adsorbed sulphur or of sulphur dioxide a special form of oxide is presumably formed which can be reduced only in the potential range where the adsorption of hydrogen takes place. The possibility of the adsorption of sulphur in multilayers is also discussed.