1. Department of Condensed Matter and Materials Physics, S. N. Bose National Centre for Basic Sciences, Block JD, Sector-III, Salt Lake, Kolkata 700 106, India
2. Department of Materials Science and Engineering, Uppsala University, Box 35, SE-751 03 Uppsala, Sweden
3. Department of Thin Films and Nanostructures, Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 162 00 Prague, Czech Republic
4. Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India