1. Department of Materials Science and EngineeringCity University of Hong Kong 83 Tat Chee Avenue Hong Kong SAR China
2. City University of Hong Kong Shenzhen Research Institute Shenzhen 518057 China
3. Department of Applied PhysicsThe Hong Kong Polytechnic University Hung Hom Hong Kong SAR China
4. Department of ChemistryCity University of Hong Kong 83 Tat Chee Avenue Hong Kong SAR China