Squeezing light through nanometre-wide gaps in metals can lead to extreme field enhancements, nonlocal electromagnetic effects and light-induced electron tunnelling. This intriguing regime, however, has not been readily accessible to experimentalists because of the lack of reliable technology to fabricate uniform nanogaps with atomic-scale resolution and high throughput. Here we introduce a new patterning technology based on atomic layer deposition and simple adhesive-tape-based planarization. Using this method, we create vertically oriented gaps in opaque metal films along the entire contour of a millimetre-sized pattern, with gap widths as narrow as 9.9 Å, and pack 150,000 such devices on a 4-inch wafer. Electromagnetic waves pass exclusively through the nanogaps, enabling background-free transmission measurements. We observe resonant transmission of near-infrared waves through 1.1-nm-wide gaps (λ/1,295) and measure an effective refractive index of 17.8. We also observe resonant transmission of millimetre waves through 1.1-nm-wide gaps (λ/4,000,000) and infer an unprecedented field enhancement factor of 25,000.
Bibliographical noteFunding Information:
This work was supported by the US Department of Defense (DARPA Young Faculty Award N66001-11-1-4152; X.S.C., N.C.L., H.I. and S.H.O.) and the National Research Foundation of Korea (SRC 2008-0062255, GRL K20815000003, 2010-0029648, 2011-0019170; H.-R.P., J.S.A., K.J.A., D.-S.K. and GRL K20815000003; X.P., Y.J.K. and N.P.). Device fabrication was performed at the University of Minnesota Nanofabrication Center, which receives support from the National Science Foundation (NSF) through the National Nanotechnology Infrastructure Network program, and the Characterization Facility, which has received capital equipment funding from the NSF through the Materials Research Science and Engineering Center. S.-H.O. also acknowledges support from the Office of Naval Research Young Investigator Award (N00014-11-1-0645), the NSF CAREER Award (DBI 1054191) and the Minnesota Partnership Award for Biotechnology. H.I. acknowledges support from the University of Minnesota Thesis Research Grant. Use of the Center for Nanoscale Materials was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We thank Reuven Gordon and Sukmo Koo for their helpful comments and David Gosztola for his valuable assistance.