Plasmonic devices can beat the diffraction limit and confine electromagnetic waves into nanometer-scale gaps. Precise and high-throughput fabrication of such extreme nanophotonic structures is challenging with even the most advanced electron-beam lithography tool. I will present unconventional approaches to produce ultranarrow plasmonic gaps by leveraging mature silicon processing technologies.
Template stripping [1] has enabled rapid production of atomically smooth patterned metals and ultrasharp tips. In this process, instead of directly patterning metal films, which are difficult to plasma-etch, we engineer inverse patterns in a silicon wafer. After metal deposition and peeling, ultrasmooth patterns in the silicon wafer are replicated onto a metal film. Ultrasmooth patterned metals have been used for near-field imaging, biosensing, and graphene plasmonics [2].
I will discuss lithographic patterning applications of ALD – atomic layer lithography – developed in our group. Using this unconventional approach, we have demonstrated wafer-scale production of centimeter-long and sub-10-nm wide gaps in various metals for sensing, optical trapping of biomolecules, and silicon-photonics-integrated plasmonic sensors.

[1] P. Nagpal, N. C. Lindquist, S.-H. Oh, D. J. Norris, Science (2009) 325, 594.
[2] I.-H. Lee, D. Yoo, Ph. Avouris, T. Low, S.-H. Oh. Graphene acoustic plasmon resonator for ultrasensitive infrared spectroscopy. Nature Nanotechnology (2019) 14-313.