1. Helmholtz Institute Ulm (HIU), Helmholtzstraße 11, D-89081 Ulm, Germany
2. Karlsruhe Institute of Technology (KIT), P.O. Box
3640, D-76021 Karlsruhe, Germany
3. Electron Microscopy Group of Materials Science, Ulm University, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
4. Chemistry Department, Sapienza University, Piazzale A. Moro 5, I-00185 Rome, Italy