1. The Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2BW, United Kingdom
2. Delmic B.V., Kanaalweg 4, 2628 EB Delft, The Netherlands
3. Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
4. Department of Materials, Imperial College London, London SW7 2BP, United Kingdom
5. Chair in Hybrid Nanosystems, Faculty of Physics, Ludwig-Maxilimians-Universität München, 80799 München, Germany