1. Department of Physics, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong
2. Department of Physics, Federal University Oye Ekiti (FUOYE), Km 3 Oye Afao road, Oye Ekiti State, Nigeria
3. Department of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong