1. School of Nano Science and TechnologyIndian Institute of Technology Kharagpur Kharagpur West Bengal 721803 India
2. Department of PhysicsIndian Institute of Technology Kharagpur Kharagpur West Bengal 721302 India
3. Surface Physics and Material Science DivisionSaha Institute of Nuclear Physics HBNI, 1/AF Bidhannagar Kolkata 700064 India
4. S. N. Bose National Center for Basic Sciences Sector‐III, Salt Lake Kolkata 700098 India