1. Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland
2. Corelab for Correlative Microscopy and Spectroscopy, Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
3. Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom
4. York Probe Sources Ltd, 7 Harwood Rd., York YO26 6QU, United Kingdom