[1] Argonne Natl Lab, Ctr Nanoscale Mat, Argonne, IL 60439 USA
[2] Penn State Univ, Dept Mat Sci, University Pk, PA 16802 USA
[3] Penn State Univ, Ctr Two Dimens & Layered Mat, University Pk, PA 16802 USA
[4] US Army Res Lab, Sensors & Electron Devices Directorate, Adelphi, MD 20723 USA
[5] Rensselaer Polytech Inst, Dept Phys Appl Phys & Astron, Troy, NY 12180 USA
[6] Penn State Univ, Dept Phys, University Pk, PA 16802 USA
[7] Penn State Univ, Dept Chem, University Pk, PA 16802 USA