1. Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095‐1569 USA
2. Department of Chemical Engineering and Department of Chemistry University of Washington Seattle WA 98195‐1750 USA
3. Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials Key Laboratory of Cluster Science of Ministry of Education School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081 China
4. California NanoSystems Institute University of California, Los Angeles Los Angeles CA 90095‐8352 USA
5. Department of Materials Science and Engineering University of California, Los Angeles Los Angeles CA 90095‐1595 USA