Surface-reconstruction-induced changes in free-carrier scattering from the W(100) surface: an infrared surface-electromagnetic-wave study

Using the infrared-absorption technique of surface-electromagnetic-wave spectroscopy (SEWS) we have studied the effects of H/sub 2/ and D/sub 2/ chemisorption on the SEW attenuation coefficient ..cap alpha.. in the 10-..mu..m region between 165 and 350 K. The change in ..cap alpha.. at room temperature has also been measured for N/sub 2/, O/sub 2/, and CO adsorption. The coverage (C-italicT-italicH-italicE-italicT-italicA-italic) dependence of ..cap alpha.. for N/sub 2/, O/sub 2/, and CO is fairly simple (either a monotonic increase (N/sub 2/) or a peak at some intermediate coverage (O/sub 2/, CO)) and points to changes in free-carrier (FC) surface scattering as the dominant ..cap alpha..-changing mechanism. Much richer structure in ..cap alpha..(C-italicT-italicH-italicE-italicT-italicA-italic) upon H/sub 2/ and D/sub 2/ adsorption is observed: A small peak followed by a sharp dip at C-italicT-italicH-italicE-italicT-italicA-italic = 0.42 monolayer (ML) (C-italicT-italicH-italicE-italicT-italicA-italic = 2 monolayers equivalentsaturation), a broad maximum at C-italicT-italicH-italicE-italicT-italicA-italic = 1.28 ML, and a value at C-italicT-italicH-italicE-italicT-italicA-italic = 2.0 ML higher than for the clean surface. For C-italicT-italicH-italicE-italicT-italicA-italic>0.42 ML the variations are dominated by reconstruction-induced changes in FC scattering from the surface.