1. Thin Film Physics Division, Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-58183 Linköping, Sweden
2. ICAMS, Ruhr-Universität Bochum, 44780 Bochum, Germany
3. Frederick Seitz Materials Research Laboratory and The Materials Science Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA