1. Department of Electrical and Electronic Engineering; Southern University of Science and Technology; Shenzhen 518055 China
2. School of Electrical and Electronic Engineering; Nanyang Technological University; 50 Nanyang Avenue 639798 Singapore Singapore
3. Physical Chemistry; Centre of Molecular Devices; Department of Chemistry; Ångström Laboratory; Uppsala University; Uppsala SE-75120 Sweden
4. School of Power and Mechanical Engineering; Wuhan University; Wuhan 430072 China
5. Institute of Materials Research and Engineering (IMRE); A*STAR; Fusionopolis Way 138634 Singapore Singapore