1. Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovoth 76100, Israel
2. Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan QLD 4111, Australia
3. Department of Physics, University of California, Berkeley, Berkeley, California 94720, United States
4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
5. Kavli Energy NanoSciences Institute at Berkeley, University of California, Berkeley, Berkeley, California 94720, United States