1. Micron School of Materials Science & Engineering, Boise State University, Boise, Idaho 83725
2. Department of Physics, Boise State University, Boise, Idaho 83725
3. Unidad Académica de Ciencia y Tecnología de la Luz y la Materia, Universidad Autónoma de Zacatecas, 98160 Zacatecas, Zac., Mexico
4. California NanoSystems Institute, University of California Los Angeles, Los Angeles, California 90095
5. Department of Electrical and Computer Engineering, Tufts University, Medford, Massachusetts 02155