1. Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095 , United States
2. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California , United States
3. Electron Imaging Center for NanoMachines, California NanoSystems Institute, University of California , Los Angeles, California , United States
4. Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory , Berkeley, California , United States