Generating plasmonic heterostructures by cation exchange and redox reactions of covellite CuS nanocrystals with Au³⁺ ions

Abstract

We demonstrate the fabrication of various types of heterostructures, including core-shells and dimers. This is achieved by reacting platelet-shaped covellite (CuS) nanocrystals (NCs) with Au ions under various reaction conditions: the exposure of CuS NCs to Au ions, in the presence or in the absence of ascorbic acid (AA), leads to the formation of CuS@Au core-shell nanostructures; the reaction of CuS NCs with Au ions in the presence of oleylamine (OM) leads to the formation of CuS@AuS; the presence of both OM and AA leads to the formation of Au/CuS dimers. Depending on which condition is chosen, either cation exchange (CE) between gold and copper ions is predominant (leading to amorphous AuS) or the reduction of Au leads to the nucleation of metallic Au domains (which are operated by the AA). In the heterostructures achieved by CE, the AuS shell is almost entirely amorphous, and can be converted to polycrystalline upon electron beam irradiation. Finally, when both oleylamine and AA are present in the reaction environment, Au/CuS dimers are formed due to the reduction of Au to metallic Au domains which nucleate on top of the CuS seeds. The experimental dual plasmonic bands of the CuS@Au core-shells and Au/CuS dimers are in agreement with the theoretical optical simulations. The procedures described here enable the synthesis of core-shell nanostructures with tunable localized surface plasmon resonances (LSPRs) in the near-infrared (NIR) region, and of plasmonic metal/semiconductor heterostructures with LSPRs in both the NIR and the visible regions.

Ion exchange: an advanced synthetic method for complex nanoparticles

“…When the metastable Cu 2−x S@Au 2 S core–shell NPs were irradiated with an electron beam, the NPs were converted into a dumbbell-like shape because the electron beam provided energy to transform them into a stable structure. The cation exchange reaction between Cu and Au in CuS was also observed by Hu et al [94]. Through the cation exchange reaction from covellite CuS, various Au–CuS NPs with heterostructures such as CuS@Au core–shell NPs, CuS@Au 2 S core–shell NPs, and an Au/CuS dimer were synthesized by using ligands such as OA and ascorbic acid (Fig.…”

“…The synthesized CdSe nanobelts exhibited rapid, stable, and repeatable photoelectric properties when used as photodetectors.

Fig. 12An illustration of the various reaction conditions and related heterostructures of Au or Au 2 S–CuS at room temperature(Reprinted with permission from the Royal Society of Chemistry [94])

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Gradual Transformation of Ag2S to Au2S Nanoparticles by Sequential Cation Exchange Reactions: Binary, Ternary, and Hybrid Compositions

“…46 It is reported to be a highly metastable phase, decomposing both under inert atmosphere and air conditions at temperatures above 420 K, and its preparation often leads to amorphous solids, with a few exceptions at the nanoscale. 46,[52][53][54] It is worth mentioning that the crystallinity of the Au2S nanostructures reported here is highly preserved at room temperature for months after preparation. Additionally, spherical and rod-like Au2S NPs with a hollow morphology like the ones described in this work have not been reported to date and, after appropriate functionalization and water transfer, they open up the doors for the use of such a priori biocompatible elongated nanostructures as potential nanocontainers for dual diagnostic and therapeutic applications, in line with our recent studies about biomedical applications of noble metal-based chalcogenides analogous to the ones described in this work.…”

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“…The purple emission band at 330-450 nm and the strong blue emission peak at 395 nm are attributed to surface defects of CuS nanocrystals. 23 As the reaction temperature increased from 120°C to 150°C, the luminescence intensity at 395 nm was attributed to the higher temperature, resulting in more defects of CuS nanocrystals. These defects enhanced the luminescence intensity of CuS nanocrystals, which indicated that the surface defect concentration of CuS nanocrystals is affected by the reaction temperature ( Figure 3A…”