Tsinghua University - Shenzhen Geim Graphene Center, Huazhong University of Science and Technology - State Key Laboratory of Coal Combustion, Tsinghua University - Shenzhen Geim Graphene Center, Tsinghua University - Shenzhen Geim Graphene Center, Huazhong University of Science and Technology - State Key Laboratory of Coal Combustion, California State University, Northridge - Department of Physics and Astronomy, California State University, Northridge - Department of Physics and Astronomy, Huazhong University of Science and Technology - State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology - State Key Laboratory of Coal Combustion, Tsinghua University - Shenzhen Geim Graphene Center and Tsinghua University - Shenzhen Geim Graphene Center