1. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
2. Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California 94720, United States
3. Nanosys, Inc., 233 South
Hillview Drive, Milpitas, California 95035, United States
4. Kavli Energy NanoScience Institute, Berkeley, California 94720, United States