Yuting Luo1, Sum Wai Chiang2, Lei Tang1, Zhiyuan Zhang1, Fengning Yang1, Qiangmin Yu1, Baofu Ding1 and Bilu Liu1,*
1 Shenzhen Geim Graphene Center (SGC), Tsinghua-Berkeley Shenzhen Institute (TBSI) and Tsinghua Shenzhen International Graduate School (TSIGS), Tsinghua University, Shenzhen, 518055 P. R. China
2 Tsinghua Shenzhen International Graduate School (TSIGS), Tsinghua University, Shenzhen, 518055 P. R. China