1. Department of Electrical & Electronic Engineering; South University of Science and Technology of China; Shenzhen 518055 P.R. China
2. School of Power and Mechanical Engineering; Wuhan University; Wuhan 430072 P.R. China
3. School of Electrical & Electronic Engineering; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
4. Physical Chemistry; Centre of Molecular Devices; Department of Chemistry; Ångström Laboratory; Uppsala University; Uppsala SE-75120 Sweden