1. Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, Quebec H3A 0E9, Canada
2. Department of Materials Science and Engineering, Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
3. Nano Electronics Lab, Samsung Advanced Institute of Technology, Suwon-si, Gyeonggi-do 443-803, Korea