1. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
2. Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA.
3. Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA.
4. Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA 16802, USA.
5. Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA.