| AVS 55th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeA |
| Session: | Structure of Oxide Surfaces and Oxide Heterostructures |
| Presenter: | C.A.F. Vaz, Yale University |
| Authors: | C.A.F. Vaz, Yale University H.-Q. Wang, Yale University C.H. Ahn, Yale University V.E. Henrich, Yale University M.Z. Baykara, Yale University T.C. Schwendemann, Yale University N. Pilet, Yale University B.J. Albers, Yale University U.D. Schwarz, Yale University L.H. Zhang, Brookhaven National Laboratory Y. Zhu, Brookhaven National Laboratory J. Wang, Yale University E.I. Altman, Yale University |
| Correspondent: | Click to Email |
The oxides of the 3d transition metals form an important class of materials with properties that depend sensitively on the cationic oxidation state and the electronic environment. As a consequence, these compounds display a multiplicity of magnetic, electronic and catalytic behavior, which makes them interesting from both fundamental and practical perspectives. In this work, we study the interface and electronic structure of thin (~20-74 nm) Co3O4(110) epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl2O4(110) single crystal substrates. Using several real and reciprocal space techniques, we show that the surface and bulk properties of [110]-oriented Co3O4 thin films depend sensitively on growth conditions and post-growth annealing. The as-grown film surfaces are found to be relatively disordered and exhibit an oblique low energy electron diffraction (LEED) pattern associated with the O-rich CoO2 bulk termination of the (110) surface. Post-annealing is found to improve considerably the film characteristics; in particular, the film surface displays sharp rectangular LEED patterns, suggesting a surface stoichiometry of the alternative Co4O4 bulk termination of the (110) surface. Non-contact atomic force microscopy demonstrates the presence of wide terraces separated by atomic steps in the annealed films that are not present in the as-grown structures; the step height of ~2.7 Å corresponds to two atomic layers and confirms a single termination for the annealed films, consistent with the LEED results. Finally, magnetic susceptibility measurements show that antiferromagnetic order is present at low temperatures, with an ordering temperature close to 47 K for the as-grown films and of about 30 K for the annealed films. Such well characterized and high quality surfaces could be employed as templates for the growth of other materials or as a model system for the study of exchange bias.