1. Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
2. School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, AZ 85287, USA
3. Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, USA
4. Theiss Research, Inc., La Jolla, CA 92037, USA