* Corresponding authors

^a Max Planck Institute for Solid State Research, Heisenbergstraße 1, DE-70569 Stuttgart, Germany
E-mail: r.merkle@fkf.mpg.de
Fax: +49 711 689 1722
Tel: +49 711 689 1768

^b Chair of Physical Chemistry, Montanuniversitaet Leoben, Franz-Josef-Straße 18, AT-8700 Leoben, Austria
E-mail: werner.sitte@unileoben.ac.at
Fax: +43 3842 402 4802
Tel: +43 3842 402 4800

^c Institute of Electron Microscopy and Nanoanalysis (FELMI), Graz University of Technology & Graz Centre for Electron Microscopy (ZFE), Steyrergasse 17, AT-8010 Graz, Austria