MERCURY SURFACE-PLASMON DISPERSION - EXPERIMENT AND THEORY

Momentum-resolved inelastic electron spectroscopy has been utilized to measure the surface-plasmon dispersion and damping for thick Hg films grown onto a Cu(100) substrate. Hg has been investigated since it off ers an opportunity to examine the effects of the crystal potential on the surface-plasmon dispersion, and to correlate the measurements on a surface with those for collective excitations in clusters. The effect s of the electronic band structure of Hg can be seen in the energy and width of the surface plasmon as a function of momentum transfer q(par allel to) Dynamical response calculations were performed for a semi-in finite electron gas where several important aspects of the crystal pot ential are taken into account in an average manner. These effects are shown to lead to an overall lowering of the plasma frequency, to a fla ttening of the momentum dispersion, and to a sizable broadening of the plasmon linewidth relative to the behavior obtained for the simple me tals. Even though the band structure effects in Hg are significant, th ere is a quantitative correlation between the normalized energy and wi dth of the surface plasmon as a function of q(parallel to) and the Mie resonance seen in Hg clusters as a function the inverse of the radius R.