1. Centre for Research
in Nanoscience and Nanotechnology, University of Calcutta, Technology Campus, Block
JD2, Sector III, Salt Lake City, Kolkata 700 098, India
2. Department
of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake
City, Kolkata 700 098, India
3. Solid
State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India