1. Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
2. School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
3. Northrop Grumman Corporation, Redondo Beach, California 90278, USA
4. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA