1. Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California, 90095-1569
2. Institute of Materials Chemistry, College of Materials Science and Engineering, Tongji University, 1239 Si-Ping Road, Shanghai 200092, China
3. School of Electrical and Computer Engineering, RMIT University, City Campus, P.O. Box 2476 V, Melbourne 3001, Victoria, Australia
4. Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, California 90095-1969, United States
5. Department of Civil and Environmental Engineering, University of California, Los Angeles, Los Angeles, California 90095-1969, United States