1. Department of Electrical Engineering and Computer Science, University of California, Berkeley, California 94720, United States
2. Department of Electrical Engineering, University of California, Los Angeles, California 90095, United States
3. Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California 90095, United States
4. Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, California 94720, United States
5. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
6. California NanoSystems Institute, Los Angeles, California 90095, United States