Observation of surface plasmons in solid and liquid mercury

Surface plasmons were observed with energies of 6.35 ± 0.1 eV in solid and 6.5 ± 0.1 eV in liquid Hg. The energies were determined by means of reflection electron energy-loss spectroscopy using a cylindrical mirror analyzer with coaxial electron gun. The solid Hg plasmon was dispersion free within experimental error, while the plasmon in the liquid showed small positive dispersion. Proof that surface plasmons were seen was obtained by observing the shift in energy when the surface was covered with dielectric layers (${\mathrm{H}}_2$O for the solid, and cetyl alcohol for the liquid). The observed shifts agree well with simple calculations.