1. Sensor System Research Center, Korea Institute of Science and Technology, Seoul 136791, South Korea
2. I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstr. 9, Hamburg 20355, Germany
3. Key Laboratory of Nanodevices, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Industrial Park, Suzhou City, Jiangsu 215123, People's Republic of China
4. Division of Electronics and Electrical Engineering, Dongguk University-Seoul, 100715 Seoul, South Korea
5. Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, Wisconsin-53706, USA
6. Center for Hybrid Nanostructures, Universität Hamburg, Jungiusstr. 11c, Hamburg 20355, Germany
7. Department of Electrical and Computer Engineering, University of Wisconsin-Madison, 1415 Engineering Dr. Madison, Wisconsin-53706, USA