1. Institute of Semiconductor Technology and Laboratory for Emerging Nanometrology (LENA), TU Braunschweig, 38106 Braunschweig, Germany
2. Institute of Organic Chemistry, Johannes Gutenberg University, 55128 Mainz, Germany
3. BAM- Federal Institute for Materials Research and Testing, Division 1.10 Biophotonics, 12489 Berlin, Germany
4. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany