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)].

Helium atom scattering experiments have been carried out on the (001) surface of KTaO(3) doped with 6, 10 and 15% Nb, produced by cleaving in situ single crystal samples. Several phenomena were observed through He atom diffraction measurements, including metastable behavior immediately after cleaving, reconstruction of a fraction of the surface to (2 × 1) domains after thermally cycling the surface temperatures, and the distribution of step heights of terraces at the surface as multiples of the unit cell dimension of ∼ 4 Å. In addition, a large hysteresis effect was found in the (100) azimuth in the variation of surface reflectivity with surface temperature; a much smaller hysteresis effect was found in the (110) azimuth. The hysteresis effects appear for all Nb doping concentrations. Finally, small oscillations in the specular and Bragg diffraction intensities near the surface temperature 80 K were also observed.

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