Stabilization of Plasmonic Silver Nanostructures with Ultrathin Oxide Coatings Formed Using Atomic Layer Deposition

Abstract

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.

Plasmonic Core–Shell–Satellites with Abundant Electromagnetic Hotspots for Highly Sensitive and Reproducible SERS Detection

“…Therefore, for Ag@Ag NPs, the LSPR valley redshifted from 407 to 412 nm due to the slight increase in the size of Ag NPs, arising from the repeated dewetting process. Compared to Ag and Ag@Ag NPs, a large redshift in the LSPR valley to 448 nm was observed for PCSS nanostructures due to the increased refractive index of the surrounding medium in the presence of an Al 2 O 3 shell [25]. Moreover, although the satellite Ag NPs are much smaller than Ag@Al 2 O 3 , the EM coupling could be largely increased due to the reduced gaps.…”

“…It was observed that the reflectance spectrum of Ag NPs shows a plasmonic valley at approximately 407 nm, which can be attributed to the LSPR mode of Ag NPs [37,38]. It is well-known that LSPR wavelength is strongly associated with the size of plasmonic NPs as well as the surrounding medium [25,38,39]. Therefore, for Ag@Ag NPs, the LSPR valley redshifted from 407 to 412 nm due to the slight increase in the size of Ag NPs, arising from the repeated dewetting process.…”

“…[21][22][23][24]. Among these SERS-active nanostructures, the plasmonic core-shell-satellite (PCSS) offers several advantages: (i) protection of the plasmonic core from oxidation, (ii) maintenance of the shape of the core even at high temperatures, (iii) tuning of LSPR properties along with the adjustment of core and satellite size, and (iv) maintenance of small nanogaps between plasmonic core and satellite, producing a strong EM field hotspot [25][26][27][28]. Therefore, PCSS exhibited improved SERS performance due to the strong EM field intensity and abundant built-in EM hotspots.…”

Hierarchically Assembled Plasmonic Metal-Dielectric-Metal Hybrid Nano-Architectures for High-Sensitivity SERS Detection

“…To maintain the specific sub-nanometer gap, a dielectric layer can be considered as a nanogap spacer between two layered plasmonic metal nanostructures-namely, metal-dielectric-metal hybrid nano-architectures [27][28][29][30]. The dielectric spacer offers several benefits: protecting the plasmonic core from oxidation, tunning the LSPR properties, and maintaining a sub-nanometer gap between metal nanostructures to obtain a strong EM hotspot [31][32][33][34]. Therefore, it is of great significance to construct a unique 3D nano-architecture SERS substrate that comprises a hierarchical assembly of plasmonic NPs, separated by a dielectric spacer, for achieving an extremely high SERS activity.…”

Elucidating Sensitivity and Stability Relationship of Gold–Carbon Hybrid LSPR Sensors Using Principal Component Analysis

“… 27 , 28 While sensitivity enhancement can be achieved using the addition of a new material, there is a trade-off in the form of short-term stability (stability of the measurement) and long-term stability (shelf life) of the Au-based LSPR. 29 − 31 This is due to the fact that Au does not have oxidation as compared to materials used to enhance its LSPR-based refractive index sensitivity. 32 This issue of stability is further amplified when the LSPR sensor requires operation in harsh chemical environments.…”