1. Shaanxi Joint Lab of Graphene, State Key Lab Incubation Base of Photoelectric Technology and Functional Materials, International Collaborative Center on Photoelectric Technology and Nano Functional Materials, Institute of Photonics & Photon-Technology, Northwest University, Xi’an 710069, P. R. China
2. Xi’an Jiao Tong University, Center of Nanomaterials for Renewable Energy, State Key Laboratory of Electrical Insulation & Power Equipment, Xi’an 710049, China