1. a Department of Physics and Institute for Functional Nanomaterials, P.O. Box 70377 , University of Puerto Rico , San Juan, PR, 00936-8377, USA
2. b Institute of Bio-and Nano-Systems (IBN1-IT) and JARA-Fundamentals of Future Information Technology , Research Centre Jülich , D-52425, Germany
3. c Department of Electrical and Computer Engineering , University of Colorado , Colorado Springs, 80918, USA