1. Department
of Electrical Engineering and Department of Chemical Engineering and
Materials Science, University of Southern California, Los Angeles, California 90089, United States
2. Department
of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China
3. National Center
for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Center
for Electron Microscopy and Microanalysis, University of Southern California, Los Angeles, California 90089, United States