1. University of Calcutta, Department of Electronic Science, 92 A. P. C Road, Kolkata 700 009, IndiabJnan Chandra Ghosh Polytechnic, Department of Science and Humanities, 7, Mayurbhanj Road, Kolkata 700023, India
2. University of Calcutta, Department of Electronic Science, 92 A. P. C Road, Kolkata 700 009, IndiacUniversity of Calcutta, Centre for Research in Nanoscience and Nanotechnology, JD-2, Salt Lake, Kolkata 700098, India