1. Department of Materials Science and Engineering National Yang Ming Chiao Tung University Hsinchu 30010 Taiwan
2. Key Laboratory of Polar Materials and Devices Ministry of Education Department of Electronics East China Normal University Shanghai 200241 China
3. State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics Tsinghua University Beijing 100084 China
4. Center for General Education National Taiwan Normal University Taipei 10610 Taiwan
5. Center for Condensed Matter Sciences and Center of Atomic Initiative for New Materials National Taiwan University Taipei 106 Taiwan
6. Integrated Service Technology Hsinchu 300 Taiwan
7. Center for Emergent Functional Matter Science National Yang Ming Chiao Tung University Hsinchu 30010 Taiwan
8. Department of Materials Science and Engineering National Tsing Hua University Hsinchu 30013 Taiwan