1. Department of Mechanical and Materials Engineering, University of Nebraska─Lincoln, Lincoln, Nebraska 68588, United States
2. Nebraska Center for Materials and Nanoscience, University of Nebraska─Lincoln, Lincoln, Nebraska 68588, United States
3. Microelectronics Research Unit, University of Oulu, FI-90014 Oulu, Finland
4. Department of Electrical and Computer Engineering, University of Nebraska─Lincoln, Lincoln, Nebraska 68588, United States