1. a Department of Physics , State University of New York at Oswego , Oswego, NY
2. b Department of Physics & Electronics , University of Puerto Rico—Humacao, Humacao, PR and the Institute for Functional Nanomaterials, University of Puerto Rico , Rio Piedras, PR
3. c Department of Physics , University of Nebraska—Lincoln , Lincoln, NE
4. d Department of Chemistry , University of Nebraska—Lincoln , NE