HREELS AND ELS-LEED STUDIES OF SURFACE-PLASMONS ON AG AND PD SINGLE-CRYSTALS

Recent progress in experimental investigation of the surface plasmon f or d-electron metals with angle resolved electron energy loss spectros copy and energy loss spectroscopy - low energy electron diffraction is reviewed. The latter technique allows to greatly improve resolution i n k-space which constitutes the major limiting factor for measuring su rface plasmon dispersion. Applying both techniques we show that for Ag the initial surface plasmon dispersion is linear and positive instead of negative as it is the case for simple metals, For single crystal s urfaces we find that the initial slope of the dispersion, the dependen ce of surface plasmon damping on transferred momentum and the dependen ce of both quantities on crystal temperature are anisotropic with resp ect to crystal face. For Ag(111) also the multipole surface plasmon co uld be identified in the spectra, in accord with the theoretical predi ction for a smooth shape of the electronic density profile at the surf ace. Surface plasmon damping is discussed and shown for Ag to follow t he anisotropy of surface plasmon dispersion. For Pd on the contrary a strong negative dispersion of the main loss feature at 7 eV was found.