1. Core Center of Excellence in Nano Imaging (CNI), University of Southern California, Los Angeles, California 90089, United States
2. Microelectronics Technology Department, The Aerospace Corporation, Los Angeles, California 90009, United States
3. Department of Physics and Astronomy, University of California, Los Angeles, California 90095, United States
4. California NanoSystems Institute, University of California, Los Angeles, California 90095, United States