1. State Key Laboratory of Optoelectronic Materials and Technologies, and the Key Laboratory of Low‐Carbon, Chemistry & Energy Conservation of Guangdong Province, School of Physics and Engineering, Sun Yat‐sen University, 135 Xingang Road, Guangzhou, 510275 (P.R. China)
2. General Motors Research and Development Center, Warren, Michigan, 48090‐9055 (USA)
3. Division of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemistry, University of Science and Technology of China, Hefei 230026 (P.R. China), Fax: (+86) 551‐3603040