1. Center for Ion Beam Applications (CIBA); Dept. of Physics; 2 Science Drive 3; National University of Singapore; 117542; Singapore
2. Dept. of Physics; Imperial College London; South Kensington; London; SW7 2AZ; UK
3. Dept. of Materials; Imperial College London; South Kensington; London; SW7 2AZ; UK
4. National Metrology Centre; 1 Science Park Drive; 118221; Singapore
5. Dept. of Electrical and Computer Engineering; 4 Engineering Drive 3; National University of Singapore; 117576; Singapore