金属上の吸着層の誘電率

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Adsorptions of CO and O2 on evaporated Ag and Cu films were studied by ellipsometry and resistivity measurements. Changes in ellipsometric angles δΔ and δΨ due to adsorption of CO or O2 were analyzed by an improved linear approximation of the stratified layer model of adsorption. The analysis deduced dielectric constants of the adsorbates. Dielectric constants ε1 obtained for chemisorbed CO and dissociatively chemisorbed oxygen are complex depending upon the wave length of incident light, though ε1 of molecular oxygen adsorbed weakly on Ag at 77K is real and close to that in liquid phase. δΔ and δΨ vary in non-linear fasions with the coverage of adsorbates. Many of coverage curves are described by the Lorentz-Lorenz equation for inhomogeneous distributions of the adsorbates. It is concluded for chemisorbed species that the real part of ε1 is negative, when a valence electron in an adsorbate forms a resonant bond with conduction electrons in a adsorbent, while the real part becomes positive, when the valence electron forms a strong covalent bond with an adsorbent surface atom. This concept is consistent with the Bennett and Penn theory.
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