1. Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA.
2. Department of Physics, University of Maryland, College Park, MD 20742, USA.
3. Department of Physics, Rowan University, Glassboro, NJ 08028, USA.
4. Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
5. Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA.