[1] School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
[2] Advanced Materials for Micro- and Nano-Systems, Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore 117576, Singapore
[3] Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
[4] School of Electrical and Electronics Engineering, Nanyang Technological University, Singapore 639798, Singapore
[5] Institute of Microelectronics, Singapore Science Park II, 11 Science Park Road, Singapore 117685, Singapore
[6] Advanced Materials for Micro and Nano-Systems, Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore 117576, Singapore