1. Department of Materials and Interfaces, Weizmann Institute, Rehovot 76100, Israel
2. Chemical Research Support Department, Weizmann Institute, Rehovot 76100, Israel
3. Peter Grünberg Institute and Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany