1. Material
Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States
2. Institute of Bioengineering
and Nanotechnology, 31 Biopolis Way,
The Nanos, Singapore 138669, Singapore
3. IBM Almaden Research
Center, 650 Harry Road, San Jose, California 95120, United States