| AVS 55th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeA |
| Session: | Structure of Oxide Surfaces and Oxide Heterostructures |
| Presenter: | S. Surnev, Karl-Franzens University Graz, Austria |
| Authors: | G. Weirum, Karl-Franzens University Graz, Austria R. Schennach, Graz University of Technology, Austria A. Winkler, Graz University of Technology, Austria I. Bako, Chemical Research Centre of the Hungarian Academy of Science, Hungary S. Surnev, Karl-Franzens University Graz, Austria F.P. Netzer, Karl-Franzens University Graz, Austria |
| Correspondent: | Click to Email |
Zinc oxide has attracted a significant scientific and technological interest since it is widely used in catalysis, gas sensing, and in the fabrication of optoelectronic devices. When the wurtzite ZnO crystal is cleaved parallel to the basal plane (0001), two structurally and chemically different surfaces are created on each side of the crystal, which are Zn- and O-terminated. The structure stabilisation mechanism of these two polar surfaces has been extensively investigated,1,2,3,4 but consensus models have not evolved yet. When prepared in a nanolayer form (1-2 monolayers thick), ZnO has been shown to adopt a hexagonal boron–nitride structure, where the Zn and O atoms are arranged in a trigonal planar (i.e. non-polar) configuration.5 Here we have studied the surface structure by scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED) of ZnO nanolayers grown on a Pd(111) surface as a function of the Zn coverage and the oxygen pressure. ZnO layers have been prepared either by reactive evaporation of Zn in oxygen atmosphere (5x10-8–5x10-6 mbar) onto the Pd substrate or by post-oxidation of Zn metal deposits, both methods yielding similar results. In the submonolayer coverage range two two-dimensional hexagonal ZnOx phases coexist on the Pd(111) surface: one of them exhibits an open honeycomb structure with a surface periodicity of ~ 11 Å, whereas the other one has a close-packed structure with a lattice constant of 3.3 Å, which is close to the bulk value of ZnO(0001) surfaces (3.25 Å). The latter phase becomes dominant at higher oxygen pressures and also at higher Zn coverages. The first ZnO monolayer on Pd(111) contains the hexagonal close-packed layer phase only and displays a (6x6) Moiré structure. At higher coverages the flat film morphology is maintained, but two different terminations are resolved in STM, which are found to show pronounced oxygen pressure dependence.
1O. Dulub et al., Surf. Sci. 519, 201 (2002)
2O. Dulub et al, Phys. Rev. Lett. 90, 016102 (2003)
3B. Meyer and D. Marx, Phys. Rev. B67, 035403 (2003)
4F. Ostendorf et al., Phys. Rev. B77, 041405 (2008)
5C. Tusche et al., Phys. Rev. Lett. 99, 026102 (2007)
*Supported by the Austrian Science Funds (FWF) via the Project P19198-N02 and the National Research Network “Nanoscience on Surfaces”.