1. Department of Materials Science and Engineering, University of California, Berkeley, CA, USA.
2. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
3. Center of Modern Analysis, Nanjing University, Nanjing, Jiangsu, China.
4. Bruker Nano Surfaces, 9625 West 76th Street, Minneapolis, MN, USA.
5. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.