1. Nanoscience Laboratory, Institute Instrumentation Centre, IIT Roorkee, Roorkee 247667, India
2. Department of Physics, Graphic Era (Deemed to be University), Dehradun, Uttarakhand 248002, India
3. Department of Physics, Netaji Subhas University of Technology, Dwarka Sector-3, New Delhi 110078, India
4. Department of Materials Science and Engineering, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States