[1] Zhejiang Univ, State Key Lab Silicon Mat, Sch Mat Sci & Engn, Cyrus Tang Ctr Sensor Mat & Applicat, Hangzhou 310027, Peoples R China
[2] Zhejiang Univ, Ctr Electron Microscope, Sch Mat Sci & Engn, Hangzhou 310027, Peoples R China
[3] Nanyang Technol Univ, Sch Mat Sci & Engn, Block N4-1,50 Nanyang Ave, Singapore 639798, Singapore
[4] Zhejiang Univ, Dept Phys, Hangzhou 310027, Peoples R China
[5] Chinese Univ Hong Kong, Dept Phys, Hong Kong 999077, Hong Kong, Peoples R China
[6] Univ Antwerp, EMAT, B-2020 Antwerp, Belgium
[7] Wuhan Univ Technol, Nanostruct Res Ctr, Wuhan 430074, Peoples R China