1. Dept. of Materials Science and Engineering, University of Illinois Urbana-Champaign , Urbana, IL , United States
2. Materials Research Lab., University of Illinois Urbana-Champaign , Urbana, IL , United States
3. Mork Family Department of Chemical Engineering and Materials Science, University of Southern California , Los Angeles, CA , United States
4. Core Center for Excellence in Nano Imaging, University of Southern California , Los Angeles, CA , United States