1. Department of Electrical and Electronic Engineering; Southern University of Science and Technology; Shenzhen 518055 China
2. Lehrstuhl für Funktionelle Materialien; Physik-Department; Technische Universität München; 85748 Garching Germany
3. School of Science and Engineering; The Chinese University of Hong Kong; Shenzhen China
4. Department of Chemistry; Southern University of Science and Technology; Shenzhen 518055 China
5. School of Electrical and Electronic Engineering; Nanyang Technological University; Singapore 639798 Singapore