1. Key Laboratory of Advanced Materials (MOE) School of Materials Science and Engineering Tsinghua University Beijing 100084 China
2. Graduate School at Shenzhen of Tsinghua University Shenzhen 518055 China
3. Department of Physics The Pennsylvania State University University Park PA 16802 USA
4. Department of Materials Science and Engineering and Center for 2‐Dimensional and Layered Materials The Pennsylvania State University University Park PA 16802 USA
5. Department of Chemistry The Pennsylvania State University University Park PA 16802 USA
6. Institute of Carbon Science and Technology Shinshu University Wakasato 4‐17‐1 Nagano 380‐8553 Japan