1. Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439;,
2. Department of Materials Science, The Pennsylvania State University, University Park, Pennsylvania 16802;,
3. Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802
4. Sensors and Electron Devices Directorate, US Army Research Laboratory, Adelphi, Maryland 20723;
5. Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180;
6. Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802
7. Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802