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. Department of Applied Science, Haldia Institute of Technology, Haldia 721657, Purba Medinipur, West Bengal, India
4. Department of Electronic Science, University of Calcutta, 92 APC Road, Kolkata 700009, India