1. Institute for Research in Electronics and Applied Physics University of Maryland College Park MD 20742 USA
2. Department of Materials Science and Engineering University of Maryland College Park MD 20742 USA
3. Department of Physics University of Maryland College Park MD 20742 USA
4. Sensors and Electron Devices Directorate U.S. Army Research Laboratory Adelphi MD 20783 USA
5. Instituto de Física Teórica (IFT) Universidade Estadual Paulista (UNESP) São Paulo SP 01140‐070 Brazil