1. Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, 10117 Berlin, Germany
2. 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA, USA
3. Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA
4. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA
5. Center for Nanoscale Science, The Pennsylvania State University, University Park, PA, USA
6. Department of Physics, The Pennsylvania State University, University Park, PA, USA