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  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 .
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.
 P. Nagpal, N. C. Lindquist, S.-H. Oh, D. J. Norris, Science (2009) 325, 594.
 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.
Sang-Hyun Oh obtained his B.S. in Physics from KAIST and Ph.D. in Applied Physics from Stanford University (advisor: Jim Plummer). After postdoctoral research at Bell Labs, Agere Systems, and UC Santa Barbara, he joined the ECE department at the University of Minnesota in 2006. Currently he is a Distinguished McKnight University Professor and a Bordeau Endowed Chair, and directs a lab focused on nanofabrication, biosensing, and nano-optics. He is a recipient of faculty awards from the Office of Naval Research, DARPA, NSF, ACS, and 3M. He was a visiting professor at Imperial College London and ETH Zurich in 2014.