1. Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708, United States
2. Engineering and Applied Physics Division, RTI International, Research Triangle Park, North Carolina 27709, United States
3. Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
4. Departamento de Física, Universidade Federal de Santa Catarina, Campus Universitário Trindade, 88040-000 Florianópolis, Santa Catarina Brazil