1. Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, United States
2. Department of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, California 94720, United States
3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095, United States
5. The California NanoSystems Institute, University of California Los Angeles, Los Angeles, California 90095, United States