1. DESY NanoLab, Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg, Germany
2. Department of Physics, University of Hamburg, Jungiusstraße 9, 20355 Hamburg, Germany
3. Institute of Advanced Ceramics, Hamburg University of Technology (TUHH), Denickestraße 15, 21073 Hamburg, Germany