Direct Laser Writing of Zero-Mode Waveguide Nanowells on an Ultrathin Antireflection Substrate

Zero-mode waveguide (ZMW) nanowells are an important structure for plasmonic enhancement, which are widely employed in single-molecule sensing. However, the fabrication of ZMW typically requires sophisticated nanofabrication equipment or an ultrafast laser. Here, by deliberately engineering freestanding ultrathin SiNx as both a substrate and antireflection layer, we develop a deterministic and low-cost method to fabricate ZMW nanowells by direct laser writing. Notably, ZMW nanowells with a size of 200 nm can be readily drilled by a continuous-wave 532 nm laser with a power of only 18.8 mW. To demonstrate the application of plasmonic enhancement, a single-layer graphene is placed on top of ZMW as an atomic resolution probe. By measuring the Raman signal of graphene, the electromagnetic field within ZMW is enhanced by a factor of 8. Moreover, we successfully transferred the fabricated nanowells onto another target substrate, which massively expanded the possible applications. This method is compatible with many optical systems, such as confocal/Raman microscopes, making it easier for researchers to obtain high-quality ZMW.