1. State Key Laboratory of Solidification Processing Center for Nano Energy MaterialsSchool of Materials Science and EngineeringNorthwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU) Xi'an 710072 P. R. China
2. School of PhysicsNorthwest University Xi'an 710127 P. R. China
3. Institute for Superconducting and Electronic MaterialsUniversity of Wollongong Wollongong NSW 2500 Australia
4. Stephenson Institute for Renewable EnergyUniversity of Liverpool Liverpool L69 7ZF UK
5. Department of Physical and Colloid ChemistryGubkin University 65/1 Leninsky Prospect Moscow 19991 Russia
6. BUAA‐UOW Joint Research Centre and School of PhysicsBeihang University Beijing 100191 P. R. China