1. Department of Materials Science and Engineering and State Key Laboratory of Terahertz and Millimeter WavesCity University of Hong Kong Kowloon Tong Hong Kong
2. Delaware Energy InstituteUniversity of Delaware Newark DE 19716 USA
3. Department of PhysicsThe University of Hong Kong Pokfulam Road Hong Kong
4. Department of Electrical EngineeringThe Hong Kong Polytechnic University Kowloon Hong Kong
5. Department of Architecture and Civil EngineeringCity University of Hong Kong Kowloon Tong Hong Kong
6. James Watt School of EngineeringUniversity of Glasgow Glasgow G12 8QQ UK