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Abstract
Electron paramagnetic resonance spectroscopy is used to characterise Mo(V) centres present on the surface of MgO(100) films grown on Mo(100) single-crystal surfaces at 600 K. The Mo(V) centres exhibiting a molydenyl group to reduce the charge imbalance with respect to the MgO lattice substitute Mg cations on regular terrace sites within the MgO(100) islands as deduced from angular-dependent measurements and spectral simulations. The observed anisotropic Zeeman and hyperfine interaction is comparable with Mo(V) centres supported on different powdered oxide surfaces such as alumina or silica. Analysis of the films grown at 300 K and subsequently annealed to elevated temperatures to improve the long-range order shows that the presence of the Mo sites on the surface is a thermally activated process. Comparison of the defect structures of the two preparation methods suggests that Mo plays a role in the relaxation of the lattice misfit between the Mo substrate and the MgO film.
Acknowledgement
A. Gonchar thanks the IMPRS ‘Complex surfaces in Materials Science’ for financial support. The authors are grateful to H.-J. Freund for his long-standing support of the project on defects on MgO surfaces. Valuable discussions with Martin Sterrer and Maxim Yulikov are also gratefully acknowledged. Support was also provided from the Cluster of Excellence ‘Unifying Concepts in Catalysis’ coordinated by Technische Universität Berlin and funded by the Deutsche Forschungsgemeinschaft.