1. School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
2. Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research (A*STAR), 71 Nanyang Drive, Singapore 638075, Singapore
3. Department of Applied Physics, College of Science, and Tianjin Key Laboratory of Low‐Dimensional Functional Material Physics and Fabrication Technology, Tianjin University, Tianjin 300072, P.R. China