1. School of Physics and Electronics; Hunan University; Changsha 410082 China
2. State Key Laboratory of Coal Conversion; Institute of Coal Chemistry; Chinese Academy of Sciences; Xi'an 030001 China
3. Material Technology Company Limited; Wing Lok Street Sheung Wan Hong Kong 999077 China
4. Fujian Strait Research Institute of Industrial Graphene Technologies; Jinjang 362200 China