Collective excitations and chemical modification of silver surfaces

Geunseop Lee, University of Pennsylvania


Silver has many unique properties distinguishing it from other metals, e.g., strong collective excitations and a high resistance to corrosion. In this research, both the surface plasmon of silver surfaces and the interaction of hydrogen with Ag surfaces have been investigated. The surface plasmon dispersion and damping on Ag(111) and Ag(110) along the (001) and $\lbrack1{\bar 1}0\rbrack$ directions, has been studied using electron energy loss spectroscopy. Contrasting to the negative dispersion of simple metals at small q$\sb{\vert\vert}$, the Ag surface plasmon dispersion is positive on both surfaces. The measured data also show that there exists a face dependence and for Ag(110), an anisotropy in the dispersion. The difference among different faces is rather distinct; the dispersion is primarily quadratic for Ag(111) unlike the linear behavior reported Ag(100). The anisotropy on Ag(110) appears in the quadratic term. While markedly different damping behavior is also seen between Ag(111), Ag(110) and Ag(100), the damping on Ag(100) shows no significant resolvable anisotropy. The anomaly of the surface plasmon of silver, as compared to simple metals, is a result of the surface electronic response which is surface specific because of its geometric and electronic structures. It is found that compared to fcc(111) transition metals, H/Ag(111) and H/Cu(111) shows distinctive chemisorption properties. The thermal desorption temperatures are significantly lower than those of transition metals, indicating weaker H-metal bonds on these surfaces. The saturation coverages are less than one monolayer (0.6 $\pm$ 0.1 ML for Ag(111) and 0.67 $\pm$ 0.03 ML for Cu(111)) and considered as a result of the interplay of weak H-metal bond with a repulsive H-H interaction. In the covalent bonding picture, the weak H-metal bonds of noble metals are due to the occupation of the H-metal d antibonding state. The observation of the antibonding state of H/Ag(111) in the photoemission spectra supports the picture. H-induced reconstructions of both Ag(111) and Cu(111) are seen in LEED and can be understood in terms of a comparison of the H-metal bond and the metal-metal bond.

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Recommended Citation

Lee, Geunseop, "Collective excitations and chemical modification of silver surfaces" (1995). Dissertations available from ProQuest. AAI9543103.