1. National University of Singapore,Department of Electrical and Computer Engineering,Singapore,117583
2. National University of Singapore,Centre for Ion Beam Applications (CIBA),Department of Physics,Singapore,117542
3. Université Polytechnique Hauts de France,Institut d'Electronique, de Microélectronique et de Nanotechnologie - Site de Valenciennes, IEMN CNRS UMR 8520,Valenciennes,France,59309