1. Carl von Ossietzky Universität Oldenburg, Institute of Physics, Oldenburg 26129, Germany
2. Federal Institute for Materials Research and Testing (BAM), Berlin 12485, Germany
3. Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin 12489, Germany
4. Department of Biomedical Engineering, Hong Kong Special Administrative Region of China, The Chinese University of Hong Kong, Hong Kong 999077, China
5. Center for Nanoscale Dynamics, Carl von Ossietzky Universität Oldenburg, Oldenburg 26129, Germany