Elastic and inelastic helium atom scattering experiments have been carried out on the KTaO 3 (001) surface, prepared by cleaving in situ under ultra high vacuum conditions. Several unusual observations were recorded in the helium diffraction studies. These include the appearance of metastable surface features immediately after cleaving ͑which decay to the stable (1ϫ1) surface after a few hours͒, the formation and dissolution of small (2ϫ1) and (1ϫ2) domains depending on the thermal history of the surface, large hysteresis in the diffraction beam intensities measured for surface temperatures between 200 K and 50 K depending on whether the surface is being warmed or cooled, and permanent changes in the diffraction intensities as a result of poling normal to the surface plane. The single-phonon energy-transfer experiments yield three surface phonon dispersion branches in the ͗100͘ and ͗110͘ high-symmetry azimuths. Calculations of the lattice dynamics using the VASP approach are described and the results are compared with the measurements.

Helium atom diffraction experiments carried out under ultrahigh vacuum conditions on a freshly cleaved (001) surface of KTaO3 reveal metastable features which decay over a period of several hours. The initial He diffraction pattern contains large scattering intensity satellite peaks very close to the specular reflection beam. As time from cleaving elapses, the satellite intensities diminish virtually to zero while the specular intensity increases, and the diffraction pattern evolves into one consistent with the (1x1) bulk termination surface. The data are compared with model calculations for scattering from a series of terraces at two heights with a distribution of terrace lengths [Surf. Sci. 384, 15 (1997)].

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