1. Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA
2. U.S. Air Force Research Laboratory, Aerospace Systems Directorate, WPAFB, OH 45433, USA
3. College of Engineering and Applied Science, Nanjing University, Nanjing, Jiangsu 210093, China
4. School of Materials Engineering, Purdue University, West Lafayette, IN 47907, USA
5. US Naval Research Laboratory, 4555 Overlook Ave, SW Washington, DC 20375, USA