1. Center of Hybrid Nanostructures (CHyN), Department of Physics, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
2. Institute of Microsystems Technology, Hamburg University of Technology, 21703 Hamburg, Germany
3. Institute for Theoretical Physics, Universität Hamburg, HARBOR, Luruper Chaussee 149, 22761 Hamburg, Germany
4. Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
5. Materials Science and Engineering, University of Wisconsin-Madison, University Ave. 1550, Madison, Wisconsin 53706, USA