Thursday, February 5, 2015

Abstract-Nanogap-enhanced Terahertz Sensing of 1-nm-thick (λ/106) Dielectric Films

ACS Photonics, Just Accepted Manuscript
DOI: 10.1021/ph500464j
Publication Date (Web): February 4, 2015
Copyright © 2015 American Chemical Society

We experimentally show that terahertz (THz) waves confined in sub-10-nm metallic gaps can detect refractive index changes caused by only a 1-nm-thick (~λ/106) dielectric overlayer. We use atomic layer lithography to fabricate a wafer-scale array of annular nanogap arrays. THz time-domain spectroscopy is used to monitor transmission spectra through these samples in conjunction with sequential depositions of 1-nm-thick Al2O3 overlayers. Using sub-10-nm annular aperture arrays, we can unambiguously measure THz resonance shifts due to a 1-nm-thick Al2O3 film. Because of the enormous mismatch in length scales between THz waves (millimeter-scale wavelength) and sub-10-nm gaps, conventional modeling techniques cannot be used to analyze our experiments. We employ an advanced finite-element-modeling (FEM) technique – Hybridizable Discontinuous Galerkin (HDG) scheme – for full three-dimensional modeling of resonant transmission of THz waves (millimeter-scale wavelength) through an annular gap that is 2 nm in width and 32 µm in diameter. Our multi-scale 3D FEM technique and atomic layer lithography will enable a series of new investigations in THz nanophotonics that has not been possible before.

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