Observation of a Soliton Reconstruction of Au(111) by High-Resolution Helium-Atom DiffractionUwe Harten, A.M. Lahee, J. P. Toennies et al.|Physical Review Letters|1985 From an analysis of diffraction data for Au(111), we deduce that the observed 23-fold periodicity in the $〈110〉$ direction can be described by a regular superstructure of one-dimensional extended stacking faults. We propose that this surface is a realization of the Frenkel-Kontorova model of competing interactions and that the periodic changes in stacking from $\mathrm{ABC}$ to $\mathrm{ABA}$ may thus take the form of solitons. The solitons, of half-width 11.8 \AA{}, lead to an average compression of 4% in the $〈110〉$ direction.
Anomalous Surface Phonon Dispersion Relations for Ag(111) Measured by Inelastic Scattering of He AtomsHigh-resolution time-of-flight measurements of 17-meV He atoms scattered from an Ag(111) surface along the $〈112〉$ and $〈110〉$ azimuths are reported. Most of the spectra reveal two sharp peaks and from their locations dispersion curves have been determined out to the zone boundary. The agreement of the lower-frequency mode with the theoretical Rayleigh dispersion curve is excellent. The other mode is significantly lower (35%) than the calculated longitudinally polarized surface mode.
Helium time-of-flight spectroscopy of surface-phonon dispersion curves of the noble metalsUwe Harten, J. P. Toennies, Christof Wöll|Faraday Discussions of the Chemical Society|1985 High-resolution inelastic scattering of low-energy (8–17 meV) helium atoms from the (111) surfaces of the three noble metals, Cu, Ag and Au, has been used to determine the surface-phonon dispersion curves for 〈112〉 and 〈110〉 azimuths out to the zone boundary. The new measurements for Cu and Au reveal two sharp dispersion curves corresponding to vibrational modes with a high spectral density at the surface, as observed previously for Ag. The lower-frequency curve is attributed to the Rayleigh mode and the higher-frequency curve to a longitudinal mode, which appears at the surface because of a significant 50–70% weakening in the lateral force constants in the uppermost surface layer. The results are compared with several recent lattice-dynamical calculations.
Observation of a Kohn Anomaly in the Surface-Phonon Dispersion Curves of Pt(111)Uwe Harten, J. P. Toennies, Christof Wöll et al.|Physical Review Letters|1985 Surface-phonon dispersion curves have been measured by He-atom inelastic scattering for Pt(111) along the $〈1\overline{1}0〉$ and $〈11\overline{2}〉$ azimuths with greatly reduced scatter compared with earlier work. Along the $〈1\overline{1}0〉$ direction the results reveal a number of anomalous kinks in the Rayleighmode dispersion curve. Comparison with the corresponding anomaly in the bulk suggests that the effect is due to a two-dimensional surface Kohn anomaly.
Surface Phonons on GaAs(110) Measured by Inelastic Helium Atom ScatteringUwe Harten, J. P. Toennies|Europhysics Letters (EPL)|1987 Surface phonon dispersion relations have been measured by He-atom inelastic scattering for in situ cleaved GaAs(110). Besides the expected Rayleigh mode and a mode at 13 meV at the Brillouin-zone boundary a third mode with a wave vector independent energy of 10 meV has been observed. This finding is very similar to our recent results for the reconstructed Si(111) (2 × 1) surface. In both cases the observations are unexpected for the presently accepted surface structures.