1. Low Energy Electronic Systems (LEES), Singapore-MIT Alliance for Research and Technology (SMART), 1 Create Way, 138602 Singapore
2. Institute of Materials Research and Engineering (IMRE), Agency for Science Technology and Research (A*STAR), 2 Fusionopolis Way, 138634 Singapore
3. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02141, United States
4. Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575 Singapore