1. Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia
2. Hunan Key Laboratory for Supermicrostructure and Ultrafast Process, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China
3. National Center for International Joint Research of Electronic Materials and Systems, Henan Key Laboratory of Laser and Opto-electric Information Technology, School of Information Engineering, Zhengzhou University, Zhengzhou, Henan 450052, P. R. China
4. Australian National Fabrication Facility ACT Node, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia