We thank L. Chen for discussions, and H. Huyan at UCI for assisting with the TEM experiments. This work was supported by the National Natural Science Foundation of China , the National Key R&D Program of China and the Fundamental Research Funds for the Central Universities . Y. Nie is supported by High Level Entrepreneurial and Innovative Talents Introduction, Jiangsu Province; C.A., X.Y. and X.P.
Lu Han, Meiyu Wang, Hanyu Fu, Tianqi Wei, Yanhan Fang, Huazhan Liu, Wei Guo, Zhengbin Gu, Yurong Yang, Peng Wang, Yanfeng Chen, Di Wu & Yuefeng Nie Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, People’s Republic of China Lu Han, Meiyu Wang, Hanyu Fu, Tianqi Wei, Yanhan Fang, Huazhan Liu, Wei Guo, Zhengbin Gu, Yurong Yang, Peng Wang, Yanfeng Chen, Di Wu & Yuefeng NieChristopher Addiego & Xiaoqing Pan
Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, AR, USADepartment of Materials Science and Engineering, University of California, Irvine, CA, USAIrvine Materials Research Institute, University of California, Irvine, CA, USADepartment of Applied Physics, The Hong Kong Polytechnic University, Hong Kong SAR, People’s Republic of ChinaPeng Wang