1. Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM Wiener Straße 12 D‐28359 Bremen Germany
2. Department 2 Biology/Chemistry University of Bremen Leobener Straße 3 D‐28359 Bremen Germany
3. Department 1 Physics/Electrical Engineering University of Bremen Otto‐Hahn‐Allee 1 D‐28359 Bremen Germany