CHARACTERIZATION OF SURFACE PHONONS ON CU(001) AND AG(001) - 1ST-PRINCIPLES PHONON CALCULATIONS WITH EXPERIMENTAL AND THEORETICAL-STUDIES OF HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTRA

A parameter-free first-principles phonon calculation is combined with a multiple-scattering electron-energy-loss-spectra calculation to characterize surface phonons of Cu(001) and Ag(001). The electron-energy-loss data on Cu(001) reveal the gap mode S6 at XBAR, which has been detected before only for Ni(001). The calculations also discover two additional surface modes on these surfaces, and the inelastic-electron-scattering cross sections of these modes are investigated. With the discovery of these modes, and knowledge about their inelastic-cross-section behavior, data of inelastic electron scattering are very satisfactorily explained. We also suggest that the mode found at XBAR could explain a recent He-atom scattering experiment. A comprehensive picture is established for the surface phonons on Cu(001) and Ag(001).