1. Department of Electrical & Computer Engineering, University of Nebraska−Lincoln, Lincoln, Nebraska 68588, United States
2. Microelectronics Research Unit, University of Oulu, FI-90014 Oulu, Finland
3. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
4. Department of Mechanical & Materials Engineering, University of Nebraska−Lincoln, Lincoln, Nebraska 68588, United States