Abstract
Helium atom diffraction from c(2 × 2) and 5 × 1 carbon overlayers has been observed and analysed to determine the surface structures. The high temperature oxidation of the W(100)-(5 × 1)C surface is characterized using elastic specular helium scattering and Auger electron spectroscopy. The oxidation reaction at 1400 K is observed to produce the lower coverage c(2 × 2) and c(3√2 × √2)R45° ordered carbon overlayers, before the formation of a surface oxide layer. Annealing of partially ordered c(2 × 2) structures with and without hydrogen exposure is examined. The helium scattering from the controversial 5 × 1 overlayer is analysed in light of several proposed structural models, and is found to be consistent only with a recently proposed missing row model. Helium diffraction intensity calculations together with temperature dependent intensity measurements determine a helium-surface potential well depth of 8 meV and an effective surface Debye temperature of 1350 K. Finally, helium atom diffraction peak splittings are reported here for the first time for scattering from a stepped c(2 × 2) carbide structure.
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