[1] Univ Southern Calif, Dept Phys & Astron, Los Angeles, CA 90089 USA
[2] Univ Chicago, Pritzker Sch Mol Engn, Chicago, IL 60637 USA
[3] Univ Southern Calif, Dept Elect & Comp Engn, Los Angeles, CA 90089 USA
[4] Univ Maryland, Dept Elect & Comp Engn, College Pk, MD 20742 USA
[5] Univ Southern Calif, Collaboratory Adv Comp & Simulat, Los Angeles, CA 90089 USA
[6] CNR, Inst Nanosci, Ctr S3, Via Campi 213-A, I-41125 Modena, Italy