1. TUM School of Natural Sciences, Department of Physics, Chair for Functional Materials, James-Franck-Str. 1, Garching 85748, Germany
2. Walter Schottky Institute and Physics Department, Technical University of Munich, Am Coulombwall 4, Garching 85748, Germany
3. Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, 1219 Zhongguan West Rd, Ningbo, Zhejiang Province 315201, P. R. China
4. Deutsches Elektronen-Synchrotron DESY, Photon Science, Notkestr. 85, Hamburg 22607, Germany
5. Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen 56-58, Stockholm SE-100 44, Sweden