title: Atomic layer lithography of wafer-scale nanogap arrays for extreme confinement of electromagnetic waves.
abstract: 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.
authors.affiliation: 1] Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA [2].
authors.forename: Xiaoshu
authors.initials: X
authors.lastname: Chen
authors.forename: Hyeong-Ryeol
authors.initials: HR
authors.lastname: Park
authors.forename: Matthew
authors.initials: M
authors.lastname: Pelton
authors.forename: Xianji
authors.initials: X
authors.lastname: Piao
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Lindquist
authors.forename: Hyungsoon
authors.initials: H
authors.lastname: Im
authors.forename: Yun Jung
authors.initials: YJ
authors.lastname: Kim
authors.forename: Jae Sung
authors.initials: JS
authors.lastname: Ahn
authors.forename: Kwang Jun
authors.initials: KJ
authors.lastname: Ahn
authors.forename: Namkyoo
authors.initials: N
authors.lastname: Park
authors.forename: Dai-Sik
authors.initials: DS
authors.lastname: Kim
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Oh