The functionality of well-tailored nanomaterials can only be retained if they are robust to the environmental factors in which they operate. The inability of Cu to withstand such factors is largely responsible for its current status as a second-tier plasmonic nanomaterial. Herein, it is demonstrated that atomic layer deposition can be used as a pliable technique for the application of oxide coatings to substrate-based Cu nanostructures where suitably protected structures become robust to oxidation, high temperatures, and aqueous, acidic, and alkaline solutions without unduly influencing important plasmonic properties. Moreover, strategies are presented for maximizing plasmonic near-fields and allowing for the transport of hot electrons while maintaining coating integrity. The findings demonstrate that there does not exist a one-solution-fits-all approach but that coating design must follow an application-specific methodology. Within the scope of the investigation, alumina, hafnia, titania, and combinations thereof were all shown to be effective under certain conditions, but where hafnia shows the greatest durability in extreme pH environments and alumina-hafnia multilayers provide Cu with protection from oxidation to temperatures as high as 600 °C. The work advances the use of Cu nanostructures as durable plasmonic materials and provides broad-based strategies for protecting other vulnerable nanomaterials from harsh environments.

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Noble metal nanoplates are a unique class of two-dimensional (2D) nanomaterials whose planar geometry serves as one of the most important nanoscale building blocks. Referred to by names such as...

Even though performance metrics position silver as the preeminent plasmonic material in the visible and near-infrared regions of the electromagnetic spectrum, it remains underutilized in applications because its properties irreversibly degrade in the environments it must operate. The emergence of shell-isolated plasmonic nanostructures as a distinct class of nanomaterials has, however, created new opportunities for the utilization of silver because its vulnerable surfaces can be encapsulated in a chemically robust transparent shell while maintaining important plasmonic properties. To fully capitalize on this opportunity requires that shell−nanostructure combinations be rationally designed where consideration is given to a parameter space encompassing nanostructure stability–property relationships. Herein, we demonstrate the layer-by-layer deposition capabilities of the atomic layer deposition (ALD) technique as a means to design shell-isolated silver nanostructures where the confined structure acts as a built-in plasmonic sensor for spectroscopically evaluating durability in air, water, and chemically aggressive environments. For all cases, appropriately designed oxide shells are shown to provide long-term stability, but where their own surface chemistry and structural integrity become limiting factors in bolstering and preserving plasmonic properties. The work, therefore, forwards the use of ALD-deposited layers for the realization of shell-isolated plasmonic nanostructures that exploit the remarkable properties of silver.

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.