Dresden 2011 – scientific programme
Parts | Days | Selection | Search | Updates | Downloads | Help
O: Fachverband Oberflächenphysik
O 91: Epitaxy and growth: Oxides and insulators
O 91.4: Talk
Thursday, March 17, 2011, 18:00–18:15, WIL C307
Strain-induced formation of mixed-oxide films — •Xiang Shao1, Niklas Nilius1, Hans-Joachim Freund1, Livia Giordano2, and Gianfranco Pacchioni2 — 1Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany — 2Università di Milano-Bicocca, Via R. Cozzi 53, 20125 Milano, Italy
By means of scanning tunneling microscopy, Auger spectroscopy and density functional theory, we have identified a new mechanism for strain relaxation in ultrathin oxide films grown on metal supports. Due to the considerable lattice mismatch of 8%, only disordered CaO films form on a Mo(001) substrate at low growth temperatures. However, annealing the system above 1000 K induces a phase transition, which becomes manifest in the occurrence of a sharp (2x2) LEED pattern and the formation of an atomically flat oxide surface. In the course of the transition, Mo from the substrate diffuses into the film and replaces 25% of the Ca ions. The resulting rocksalt-type Ca0.75Mo0.25O structure has a negligible lattice mismatch with the Mo(001) and is in perfect registry with the support. Apart from the strain release, the oxidation of Mo atoms provides a strong thermodynamic incentive for the phase transition. A similar behavior is not observed for MgO films grown on Mo(001), where the original lattice mismatch is smaller.