1. Department of Materials Science and Engineering, Uppsala University, Box 35, SE-751 03 Uppsala, Sweden
2. Department of Thin Films and Nanostructures, Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 162 00 Prague, Czech Republic
3. Physics Department, University of Gothenburg, 412 96 Gothenburg, Sweden
4. Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India