1. Department of Chemistry, Indian Institute of Technology-Guwahati, Kamrup, Assam 781039, India
2. Institute of Nanotechnology (INT) & Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
3. Centre for Nanotechnology, Indian Institute of Technology-Guwahati, Kamrup, Assam 781039, India