Surface structure of lithium-doped potassium tantalate using helium atom scattering

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-[Angstrom] unit-cell dimension rather than multiples of the approximately 2-[Angstrom] 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 [left angle bracket]100[right angle bracket] azimuth a short time after cleaving samples at room temperature, indicating that domains with (2x1) structure had formed.