1. Department of Electrical and Computer Engineering, University of Alabama in Huntsville, Huntsville, Alabama 35899, USA
2. Sensors Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio 45433, USA
3. Solid State Scientific Corporation, Nashua, New Hampshire 03060, USA
4. Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA