Wafer scale fabrication of highly dense and uniform array of sub-5 nm nanogaps for surface enhanced Raman scatting substrates

Abstract

Metallic nanogap is very important for a verity of applications in plasmonics. Although several fabrication techniques have been proposed in the last decades, it is still a challenge to produce uniform nanogaps with a few nanometers gap distance and high throughput. Here we present a simple, yet robust method based on the atomic layer deposition (ALD) and lift-off technique for patterning ultranarrow nanogaps array. The ability to accurately control the thickness of the ALD spacer layer enables us to precisely define the gap size, down to sub-5 nm scale. Moreover, this new method allows to fabricate uniform nanogaps array along different directions densely arranged on the wafer-scale substrate. It is demonstrated that the fabricated array can be used as an excellent substrate for surface enhanced Raman scatting (SERS) measurements of molecules, even on flexible substrates. This uniform nanogaps array would also find its applications for the trace detection and biosensors.

Plasmonic Nanogaps: From Fabrications to Optical Applications

“…One of the promising applications is using nanogap structures as the substrate for the SERS, and SERS has been used from single‐molecule detection to multiplexed target detection applications . SERS is the amplified Raman scattering by molecules adsorbed on metal surfaces, and it is widely believed that EM and chemical enhancement mechanisms that are based on the excitation of localized surface plasmons and the formation of charge‐transfer complexes, respectively, are responsible for the SERS .…”

“…The subwavelength “hot spots” with highly confined energy are easily generated in the gaps, resulting in the enhancement of EM fields by orders of magnitude. This intriguing capability was essential to enable applications in surface enhanced spectroscopy, sensing, imaging, nonlinear optics, optical trapping, and metamaterials . In view of the remarkable advantages and broad application prospects, tremendous efforts have been devoted to fabricate various nanogaps.…”

Wafer-scale fabrication of high-quality tunable gold nanogap arrays for surface-enhanced Raman scattering

“…Nanometer-sized metallic nanogaps made of gold (Au) or silver (Ag) have found many applications including biomedical and chemical sensing, 1 surface-enhanced Raman spectroscopy, [2][3][4][5][6][7] and nonlinear optics 8 due to their remarkable electrochemical and optical properties. For the surfaceenhanced Raman spectroscopy, the intensity of the Raman scattering signal is boosted due to the modified emission of the scattering signal and the improved excitation of the studied molecules caused by the near-fields generated in metallic nanogap regions.…”

“…2,3 Many methods have been reported to fabricate metallic nanogap structures, such as electron beam lithography (EBL), 5 EBL-based angular deposition, 4 electrochemical deposition, 12 electromigration, 13 break junction, 14,15 and atomic layer deposition (ALD). 2,7 EBL-based methods offer a high feasibility in designing the size, position, shape and orientation of the metal nanogaps. However, their feature of serial patterning limits their use for high-yield and low-cost fabrication of large-area metal nanogap arrays.…”

Fabrication and analysis of metallic nanoslit structures: advancements in the nanomasking method

“…A variety of self-assembly techniques have emerged as promising candidates for large-area fabrication of high densities of nanogaps, some even with control over gap sizes. [37][38][39][40][41][42][43][44] The ideal fabrication technique would perfectly couple the dimensional control of methods such as lithography with the rapid and large-scale, simultaneous creation of the desired nanostructures and nanoslits.…”