Plasmonic Gold Trimers and Dimers with Air-Filled Nanogaps

Abstract

The subwavelength confinement of light energy in the nanogaps formed between adjacent plasmonic nanostructures provides the foundational basis for nanophotonic applications. Within this realm, air-filled nanogaps are of central importance because they present a cavity where application-specific nanoscale objects can reside. When forming such configurations on substrate surfaces, there is an inherent difficulty in that the most technologically relevant nanogap widths require closely spaced nanostructures separated by distances that are inaccessible through standard electron-beam lithography techniques. Herein, we demonstrate an assembly route for the fabrication of aligned plasmonic gold trimers with air-filled vertical nanogaps having widths that are defined with spatial controls that exceed those of lithographic processes. The devised procedure uses a sacrificial oxide layer to define the nanogap, a glancing angle deposition to impose a directionality on trimer formation, and a sacrificial antimony layer whose sublimation regulates the gold assembly process. By further implementing a benchtop nanoimprint lithography process and a glancing angle ion milling procedure as additional controls over the assembly, it is possible to deterministically position trimers in periodic arrays and extend the assembly process to dimer formation. The optical response of the structures, which is characterized using polarization-dependent spectroscopy, surface-enhanced Raman scattering, and refractive index sensitivity measurements, shows properties that are consistent with simulation. This work, hence, forwards the wafer-based processing techniques needed to form air-filled nanogaps and place plasmonic energy at site-specific locations.

Large‐Area Periodic Arrays of Atomically Flat Single‐Crystal Gold Nanotriangles Formed Directly on Substrate Surfaces

“…Additional details regarding simulations can be found elsewhere. [75] Instrumentation: Secondary electron SEM images were obtained using a Helios G4 Ux SEM/FIB workstation (FEI). TEM images and the associated SAED patterns were acquired using a Spectra 30-300 (S)TEM (ThermoFisher Scientific) operating at 300 keV.…”

Plasmonic Biosensors with Nanostructure for Healthcare Monitoring and Diseases Diagnosis

“…One example is the aligned trimers composed of Au nanostructures proposed by Zachary’s group ( Figure 1 a,b), which was achieved via sequential deposition of Sb and Au, high-temperature assembly process, PVD, ALD, GLAD and wet-etching processes ( Figure 1 c). They also extended the approach to manufacturing periodic trimer and dimer arrays through nanoimprint lithography technology [ 24 ].…”

“…( c ) The schematic diagram of manufacturing process. Reproduced with permission from reference [ 24 ]. Copyright 2022 American Chemical Society.…”

Generalization of Self‐Assembly Toward Differently Shaped Colloidal Nanoparticles for Plasmonic Superlattices

“…Moreover, the spatial resolution of EBL is too low for fully taking advantage of strong plasmonic coupling between NPs. [11][12][13] Lately, several chemical growth techniques, such as vaporor liquid-phase assembly, have been applied to synthesise single NPs of various shapes, such as circular, [14] triangular, [15,16] hexagonal, [17] spiral [18,19] and star-shaped [20] geometries. In a recent publication, Neal et al demonstrate the synthesis of regular large-area, single triangular particle arrays, formed by EBLassisted liquid-phase growth.…”