| Summary: | The adsorption of oxygen at room temperature onto clean (100) and (111) surfaces of copper has been studied using low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). By combining an energy-analysing Faraday cup with a commercial LEED display a versatile LEED experimental system has been obtained. Detailed intensity-energy spectra for several diffraction beams have been obtained from clean, ordered (100) and (111) copper surfaces and compare favourably with previous experimental studies and also with current dynamical calculations. Certain features existing in secondary electron spectra from copper surfaces have been identified by their unique temperature dependence as diffraction effects rather than Auger features. Although no ordered oxygen structures were observed on the copper (111) surface, two ordered structures were observed on the (100) surface: a (√2x √2)R45o structure following oxygen exposures of lx10-5 torr-minutes .and a (2x2) structure following oxygen exposures of 1 x10-4 torr-minutes. The latter structure has not been reported by other workers. Detailed intensity-energy spectra have been obtained from these surfaces, particularly from the (√2x √2)R45o structure which has been preliminarily interpreted by dynamical calculations as a reconstructed surface. A new Auger peak at 79 eV, associated with low oxygen coverages, has been observed on the copper (111) surface and attributed to a copper-oxygen cross-transition. The constant momentum averaging scheme has been applied to both the clean and oxygen adsorbed (100) and (111) surfaces of copper and the differences between the clean and adsorbate averages has been interpreted using pseudo-kinematical calculations. The resu1t~ of the analysis of three adsorbate structures, which are the first structural analyses performed on unknown surface structures using this technique, have all been physically reasonable solutions. The energy-analysing facility of the Faraday cup has enabled the first observation of anisotropies in the angular distribution of Auger electron emission from a single crystal surface. Crystallographically associated anisotropies have been observed in the 62 eV copper Auger emission from both the (100) and (111) copper surfaces. The effect of adsorbates has been briefly examined.
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