1. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China
2. School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 China
3. Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China
4. Materials Science Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
5. Molecular Foundry Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
6. Department of Materials Science and Engineering University of California Berkeley Berkeley CA 94720 USA
7. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 China