1. Photonics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
2. Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany
3. Materials Metrology Division, Instituto Nacional de Metrologia Qualidade e Tecnologia (INMETRO), 25250-020 Duque de Caxias, RJ, Brazil
4. School of Materials Science and Engineering, State Key Laboratory of Optoelectronic Materials and Technologies, Nanotechnology Research Center, Guangzhou Key Laboratory of Flexible Electronic Materials and Wearable Devices, Sun Yat-sen University, Guangzhou 510275, P. R. China
5. Faculty of Physics, Universität Wien, 1090 Wien, Austria
6. Department of Physics, Humboldt Universität zu Berlin, 12489 Berlin, Germany