1. Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
2. Applied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
3. Department of Geosciences, Princeton University, Princeton, New Jersey 08544, United States
4. RF Technology Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
5. School of Engineering, Brown University, Providence, Rhode Island 02912, United States
6. Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States