1. National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia
2. Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
3. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB30FS, U.K.
4. Electron Spectroscopy and Nanoscopy, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy