1. Department of Materials Science and Engineering, University of California, Berkeley, California 97420, United States
2. California Institute for Quantitative Biosciences, University of California, Berkeley, California 97420, United States
3. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 97420, United States
4. Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain