1. Division
of Physics and Applied Physics, School of Physical and Mathematical
Sciences, Nanyang Technological University, Singapore 637371
2. Department
of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, United States
3. Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
4. Energy
Research Institute at NTU, Interdiciplinary Graduate School, Nanyang Technological University, Singapore 637141
5. School
of Materials Science and Engineering, Nanyang Technological University, Singapore 639798
6. NOVITAS,
Nanoelectronics Centre of Excellence, School of Electrical and Electronic
Engineering, Nanyang Technological University, Singapore 639798