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.
The structures of the (001) surface of potassium tantalate doped with nominally 2%, 4%, and 7% lithium have been investigated using high-resolution helium atom scattering. The surfaces were prepared by cleaving single-crystal samples in situ under UHV conditions. Diffraction measurements in the region around the He specular reflection angle soon after cleaving yielded specular peaks initially with broad shoulders. However, over a period of about an hour, the shoulders diminished into the background. Drift spectra measurements of the stabilized surfaces revealed that the step heights separating surface terraces were predominantly multiples of the approximately 4-Å unit-cell dimension rather than multiples of the approximately 2-Å half-unit-cell dimension expected from the cleaving of these crystals. Together, these results suggest that these surfaces are rapidly modified after cleaving by migration of ions to the surface from the near surface. Further, half-order diffraction peaks were observed in the 100 azimuth a short time after cleaving samples at room temperature, indicating that domains with (2 × 1) structure had formed.
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