AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA10
Surface Phonons and Surface Phase Transitions in KTaO@sub3@ (001)

Thursday, November 5, 1998, 5:00 pm, Room 309

Session: Oxide Growth and Structure
Presenter: J.A. Li, Florida State University
Authors: J.A. Li, Florida State University
E.A. Akhadov, Florida State University
T.W. Trelenberg, Florida State University
S.A. Safron, Florida State University
J.G. Skofronick, Florida State University
L.A. Boatner, Oak Ridge National Laboratory
Correspondent: Click to Email
Phase transitions of the (001) surface of KTaO@sub3@, prepared by cleaving a single crystal sample in situ, have been investigated by high-resolution Helium Atom Scattering (HAS). Angular distribution measurements of the diffractive scattering show that thermal cycling of the sample from room temperature to low temperatures (@<=@140 K) and back to @>=@220 K induces the (1x1) surface found after cleaving at ~300 K to reconstruct to a (2x1) surface. The reconstruction appears to occur much more rapidly, minutes vs. days, when the temperature is cycled to above ~250 K. The (2x1) phase appears to be stable until ~365 K at which point the surface reverts partially to the (1x1) structure. A time-of-flight technique was employed to measure the helium atom-single phonon creation/annihilation scattering events in order to examine the surface phonon dispersion of this surface. Experiments were carried out over the temperature range of 80 to 220 K. For bulk KTaO@sub3@ considerable softening near the Brillouin zone center of the transverse optical phonon branch had been reported as the temperature was reduced. For the surface, the observed softening in the surface phonon branches is not as great, but it appears to become more pronounced as the temperature is raised from 80 to 220 K. The implications of the temperature behavior of the surface lattice dynamics and the surface phase transitions are discussed.@footnote1@ @FootnoteText@ @footnote1@ Work supported in part by US DOE grant No. DE-FG02- 97ER45635.