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 (NPU); Xi'an 710072 P. R. China
2. School of Metallurgy and Environment; Central South University; Changsha 410083 P. R. China
3. Department of Materials Science and NanoEngineering; Rice University; Houston TX 77005 USA
4. Department of Mechanical Engineering; University of Delaware; Newark DE 19716 USA