1. Department
of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore
2. Department
of Physics, Indian Institute of Technology, Madras, Chennai, 600036, India
3. Centre
for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371, Singapore
4. Center
for Nanoparticle Research, Institute for Basic Science (IBS), and
School of Chemical and Biological Engineering, Seoul National University, Seoul 151-742, Korea