1. Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 91355, United States
2. Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, United States
3. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
4. Core Center of Excellence in Nano Imaging (CNI), University of Southern California, Los Angeles, California 90089, United States
5. U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, District of Columbia 20375, United States