1. Physikalisch-Technische Bundesanstalt, Braunschweig D-38116, Germany
2. Laboratory of Emerging Nanometrology (LENA) TU Braunschweig, Braunschweig D-38106, Germany
3. Institute of Applied Physics, TU Braunschweig, Braunschweig D-38106 ,Germany
4. Institute of Technical Chemistry, TU Braunschweig, Braunschweig D-38106, Germany
5. Institute of Chemistry, University of Potsdam, Potsdam D-14476, Germany