Ir140

Plasmonic antenna samples are prepared with electron beam lithography on a microscope cover glass. We spin coat first a 200-nm thick double layer PMMA (chain lengths 250,000 and 950,000) and then a 30-nm thick layer of conductive polymer (eSpacer 300Z) to avoid charging of the sample during exposure. After exposure and development, 2 nm chromium as adhesion layer and 40 nm of gold are thermally evaporated. A lift-off process removes the excess metal. For the fluorescent film, IR140 (Sigma-Aldrich) is blended into PMMA (950,000 chain length) at a concentration of 2 mg ml⁻¹ and spin coated on the sample, forming a 60-nm thick layer. For the fluorescent disks, IR140 is blended into ARN 7520 resist (Allresist) at a concentration of 2 mg ml⁻¹. We then use alignment marks, which we have processed together with the gold antennas in order to align the coordinate system in a second electron beam lithography step. This allows us to pattern 60 nm high-fluorescent disks and to position them with 10 nm accuracy50 (link). As a final step, we cover the sample with immersion oil (Olympus).