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 and Photon-Technology, Northwest University, Xi'an 710069, China
2. Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden
3. School of Electronic Engineering, Xi'an University of Posts and Telecommunications, Xi'an 710121, China