1. Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
2. Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, USA
3. Department of Optical Science and Engineering, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, China
4. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
5. Department of Physics and Astronomy, California State University, Northridge, California 91330, USA
6. Inston, Inc., Los Angeles, California 90095, USA