1. Department of Physics, Triveni Devi Bhalotia College, Raniganj 713347, West Bengal, India
2. International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan
3. Transmission Electron Microscopy Station, NIMS, 1-2-1, Sengen, Tsukuba 305-0047, Japan
4. Department of Physics, Chuo University, 1-13-27 Kasuga,
Bunkyo, Tokyo 112-8551, Japan
5. Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-0814, Japan