1. Department of Physics, City University of Hong Kong, Kowloon 999077, Hong Kong SAR, China
2. Department of Physics, Federal University Oye-Ekiti, Oye-Ekiti, Ekiti State 3600001, Nigeria
3. Department of Biomedical Sciences, City University of Hong Kong, Kowloon 999077, Hong Kong SAR, China
4. Department of Physics, University of Chittagong, Chittagong 4331, Bangladesh
5. Department of Material Science and Engineering and State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon 999077, Hong Kong SAR, China
6. Department of Chemistry, City University of Hong Kong, Kowloon 999077, Hong Kong SAR, China
7. James Watt School of Engineering, University of Glasgow, Glasgow G12 8QQ, United Kingdom