1. CAS Center for Excellence in Nanoscience and CAS Key Laboratory of Standardization and Measurement for Nanotechnology National Center for Nanoscience and Technology Beijing 100190 P.R. China
2. Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore
3. Center for Programmable Materials School of Materials Science & Engineering Nanyang Technological University Singapore 639798 Singapore
4. State Key Laboratory of Silicon Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 P.R. China
5. NOVITAS Nanoelectronics Centre of Excellence School of Electrical and Electronic Engineering Nanyang Technological University Singapore 639798 Singapore
6. Energy Research Institute @ NTU (ERI@N) Nanyang Technological University 50 Nanyang Drive Singapore 637553 Singapore