1. Department of Physics, Southern Illinois University, Carbondale, Illinois 62901, United States
2. Department of Physics and Center for 2-Dimensional
and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
3. Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
4. Department
of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States