1. Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, United States
2. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
3. Department of Material Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States
4. Center for 2D and Layered Materials, Center for Atomically Thin Multifunctional Materials and the Two-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, Pennsylvania 16802, United States