1. Institute of Physical Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany
2. Schunk Carbon Technology, Schunk GmbH, D-35452 Heuchelheim, Germany
3. Helmholtz Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany
4. Center for Materials Research (LaMa), Justus Liebig University, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany