1. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
2. Department
of Mechanical and Aerospace Engineering, University of California, Irvine, California 92697, United States
3. The Molecular Foundry, Materials Sciences
Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Kavli Energy Nanosciences Institute, Berkeley, California 94720, United States