1. Department
of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore
2. Departamento
de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
3. National Metrology Centre, 1 Science
Park Drive, 118221, Singapore
4. Center for
Ion Beam Applications (CIBA), Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore