1. State Key Laboratory of Solidification Processing Center for Nano Energy Materials School of Materials Science and Engineering Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene Xi'an 710072 P. R. China
2. Chongqing Innovation Center Northwestern Polytechnical University Chongqing 401135 P. R. China
3. Materials Institute of Atomic and Molecular Science Shaanxi University of Science and Technology Xi'an 710021 P. R. China
4. School of Materials Science and Engineering Shaanxi University of Science and Technology Xi'an 710021 P. R. China