1. Department of Physics, University of California, Berkeley, California 94720, United States
2. Molecular
Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, United States
4. Centro de Nanociencia y Nanotecnologia, Universidad de las Fuerzas Armadas-ESPE, Sangolqui, P.O. Box 171-5-231B, Ecuador
5. Kavli Energy NanoSciences Institute at
Berkeley, University of California, Berkeley, California 94720, United States