Large‐Scale Sub‐1‐nm Random Gaps Approaching the Quantum Upper Limit for Quantitative Chemical Sensing

Abstract

Metallic nanostructures with nanogap features can confine electromagnetic fields into extremely small volumes. In particular, as the gap size is scaled down to sub‐nanometer regime, the quantum effects for localized field enhancement reveal the ultimate capability for light–matter interaction. Although the enhancement factor approaching the quantum upper limit has been reported, the grand challenge for surface‐enhanced vibrational spectroscopic sensing remains in the inherent randomness, preventing uniformly distributed localized fields over large areas. Herein, a strategy to fabricate high‐density random metallic nanopatterns with accurately controlled nanogaps, defined by atomic‐layer‐deposition and self‐assembled‐monolayer processes, is reported. As the gap size approaches the quantum regime of ≈0.78 nm, its potential for quantitative sensing, based on a record‐high uniformity with the relative standard deviation of 4.3% over a large area of 22 mm × 60 mm, is demonstrated. This superior feature paves the way towards more affordable and quantitative sensing using quantum‐limit‐approaching nanogap structures.

Ultraflat Sub-10 Nanometer Gap Electrodes for Two-Dimensional Optoelectronic Devices

“…Compared to those methods, atomic layer lithography, taking advantage of the ALD technique for forming solid dielectric films with atomic precision, allows the fabrication of sub-10 nm gaps uniformly over large regions in a controllable and reproducible manner. Many promising optical applications based on the highly enhanced electric field inside nanogaps have been successfully demonstrated using atomic layer lithography, such as extraordinary optical transmission, strong light absorption, and ultrasensitive molecular detection. − In our work, in addition to the versatile optical applications, atomic layer lithography is utilized to provide a short-channel device platform for 2D materials.…”

Surface-enhanced Raman spectroscopy of one and a few molecules of acid 4-mercaptobenzoic in AgNP enabled by hot spots generated by hydrogen bonding

“…The gap separating the surfaces of two nanospheres was taken as 1.56 nm (twice the size of 4-MBA molecule. 35 Simulated SERS enhancement factors were transformed to SERS intensities for correlation with the experimental data. The transformation were performed according to: 36 Where F HS, i is the SERS enhancement factor at the i th randomly generated HS in an aggregate (nanoparticle cluster), which was calculated assuming the E 4 -approximation.…”

“…The gap separating the surfaces of two nanospheres was taken as 1.56 nm (twice the size of 4-MBA molecule. 35 Simulated SERS enhancement factors were transformed to SERS intensities for correlation with the experimental data. The transformation were performed according to: 36…”

Statistical Strategy for Quantitative Evaluation of Plasmon-Enhanced Spectroscopy

“…On the other hand, a series of assembling and nanofabricating techniques can improve the uniformity of nanostructures with a well-defined pattern, enabling the reproducible output from SPR hot spots . For example, electron beam lithography is used to prepare metal nano-arrays with gaps exceeding 4 nm. , Besides the well-defined arrays, in complex and disorder structures with a large number of hot spots, − such as three-dimensional (3D) hot spot matrix structures ,− and core-satellite structures, − the randomness in structures remains unpredictable and inevitable …”

“…22 For example, electron beam lithography is used to prepare metal nano-arrays with gaps exceeding 4 nm. 23,24 Besides the welldefined arrays, in complex and disorder structures with a large number of hot spots, 25−27 such as three-dimensional (3D) hot spot matrix structures 20,28−30 and core-satellite structures, 31−36 the randomness in structures remains unpredictable and inevitable. 37 In simulation, most traditional SPR simulations are limited to relatively simple nanostructures composed of a few particles, but influence of the ensemble effect of complex structures on the average field enhancement and the its fluctuation is crucial to the performance of actual large-scale samples.…”