1. Department of Chemistry and Material Science & Engineering Program, University of California—Riverside, Riverside, California 92521, United States
2. Department of Materials Science and Engineering, Stanford University, Stanford, California 94304, United States
3. Nano-Device Laboratory, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, United States
4. Center for Terahertz Research and Applications, Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw 01-142, Poland