1. Institute of Experimental and Applied Physics, Kiel University, Kiel 24098, Germany
2. Delmic B.V., Kanaalweg 4, Delft 2628 EB, The Netherlands
3. Ruprecht Haensel Laboratory, Deutsches Elektronen-Synchrotron DESY, Hamburg 22607, Germany
4. Kiel, Nano, Surface, and Interface Science, Kiel University, Kiel 24098, Germany