Observation of a Metastable Periodic Structure for the (001) Surface ofKTaO3after CleavingIn Situ

Abstract

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)].

Surface structure and dynamics ofKTaO3(001)

“…Further, they are essentially the same for all surface azimuths and, moreover, that they vary only slightly from sample to sample ͑or from cleave to cleave͒. 28 The only significant deviation in satellite positions seems to come from a sample cleaved at 190 K instead of at room temperature. ͑All the other samples used in the experiments reported here were cleaved at ambient room temperature.͒ This sample gave satellites at somewhat smaller ⌬K positions, which imply larger spacings for the metastable periodic structures responsible for the satellite peaks.…”

“…Some of the results from measurements taken immediately after cleaving have already been published. 28 Additional measurements on the metastable periodic surface structures are presented below.…”

“…Preliminary experiments employing HAS on the cleaved KTaO 3 (001) surface carried out in this laboratory have recently been reported. 28 These describe the diffraction evidence for metastable features that appear at the surface immediately after cleaving and disappear after only a few hours. Metastable features observed in the diffraction scans were also noted in the KMnF 3 work, 18 but the mechanism for their disappearance seems to be somewhat different.…”

“…28 Briefly, the treatment assumes ͑i͒ that the cleavage produces islands of one surface, say KO, surrounded by terraces of the other surface, TaO 2 , ͑ii͒ that the distributions of island sizes and spacings are roughly Gaussian, and ͑iii͒ that migration of potassium ͑and oxygen͒ from the bulk to the surface increases the sizes of the KO terraces while diminishing the sizes of the TaO 2 terraces. Applying the mathematical results obtained by Croset and de Beauvais to the elastic helium scattering gives quite good agreement with our data.…”

Helium Atom Scattering from Oxide Surfaces

“…Similar studies of both surface structure and dynamics were performed on clean NiO, CoO, TiO 2 and KTaO 3 . [52][53][54][55][56] Herein, however, the focus shall be shifted to more reactive systems, which are imbedded in a larger scale project on heterogeneous catalysis.…”