1. Institut für Bio- und Nanosysteme (IBN), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany, JARA—Fundamentals of Future Information Technology, 52425 Jülich, Germany, MESA+ Institute for Nanotechnology, University of Twente, Hogekamp 7256, 7500 AE Enschede, The Netherlands, and Kavli Institute of Nanoscience, Technical University Delft, Delft, 2628 CJ, The Netherlands