Regensburg 2004 – wissenschaftliches Programm
O 25.2: Vortrag
Dienstag, 9. März 2004, 16:00–16:15, H39
Nucleation of Sub-monolayer YBa2Cu3O7−δ Films on SrTiO3(001) Probed by X-ray Standing Waves and XPS — •Sebastian Thiess, Tien-Lin Lee, Bruce C. C. Cowie, and Jörg Zegenhagen — ESRF, Grenoble, France
Before epitaxial film growth commences, nucleation of complex materials such as YBCO is necessary. The first layer then acts as a seed for the growth of the epitaxial film. Investigating the nucleation can shed some light on the relationship between the growth mode and the structure of such epitaxial systems.
Scanning tunneling microscopy (STM) and spectroscopy (STS) have suggested that submonolayers of YBCO deposited on STO(001) surfaces first nucleate as a cubic, semiconducting phase of a mixed perovskite composition, which in a second step transforms into the orthorhombic, metallic YBCO phase when the film thickness exceeds one monolayer.
We obtained complementary real space information by the x-ray standing wave technique that uses an interference field typically generated by the superposition of two x-ray waves during Bragg reflection. By monitoring the photoabsorption process via photoemission and fluorescence, we measured the atomic structure of two YBCO films, 0.5 and 1.0 monolayers thick, grown in situ onto STO(001) surfaces by PLD. Measurements were carried out in UHV at beamline ID32 at the ESRF for a variety of different STO(hkl) reflections at photon energies between 2.7 and 5.5 keV. Element-specific crystallograhic distributions were obtained for the constituent atoms of the films by direct Fourier transform.