1. T. J. Watson Laboratory of Applied Physics and Kavli Nanoscience Institute, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
2. IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
3. Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
4. Department of Physics and Astronomy, University of Missouri Columbia, Columbia, Missouri 65211, United States
5. Department of Electrical and Computer Engineering, University of Massachusetts Amherst, 151 Holdsworth Way, Amherst, Massachusetts 01003, United States
6. Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, United States