1. Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM 87131, USA.
2. U.S. Naval Research Laboratory, Washington, DC 20375, USA.
3. Department of Physics, University of Maryland, College Park, MD 20742, USA.
4. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA.
5. Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA.
6. Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA.