Surface phonons in GaAs(110).

Surface phonon dispersion curves have been measured along the , , and azimuths of GaAs(110). Features of note include a very low frequency (5.5 meV at zone boundary) surface acoustic mode in the first two directions; this may arise through the known (1x1) reconstruction of this surface. A higher frequency surface mode (7.3-8.8 meV, depending on azimuth) is seen in all directions. The helium scattering intensities are greatly influenced by bound state resonances. A careful survey of the selective adsorption signatures in extremely high resolution scans of polar angle, azimuthal angle, and incident beam wavevector allows the bound state energies to be determined with some confidence. Initial results indicate energies of roughly 1,2, and 4 meV.