Analytical modeling of localized surface plasmon resonance in heterostructure copper sulfide nanocrystals

Abstract

Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals is a relatively new field of investigation that promises greater tunability of plasmonic properties compared to metal nanoparticles. A novel process by which the LSPR in semiconductor nanocrystals can be altered is through heterostructure formation arising from solution-based cation exchange. Herein, we describe the development of an analytical model of LSPR in heterostructure copper sulfide-zinc sulfide nanocrystals synthesized via a cation exchange reaction between copper sulfide (Cu(1.81)S) nanocrystals and Zn ions. The cation exchange reaction produces dual-interface, heterostructure nanocrystals in which the geometry of the copper sulfide phase can be tuned from a sphere to a thin disk separating symmetrically-grown sulfide (ZnS) grains. Drude model electronic conduction and Mie-Gans theory are applied to describe how the LSPR wavelength changes during cation exchange, taking into account the morphology evolution and changes to the local permittivity. The results of the modeling indicate that the presence of the ZnS grains has a significant effect on the out-of-plane LSPR mode. By comparing the results of the model to previous studies on solid-solid phase transformations of copper sulfide in these nanocrystals during cation exchange, we show that the carrier concentration is independent of the copper vacancy concentration dictated by its atomic phase. The evolution of the effective carrier concentration calculated from the model suggests that the out-of-plane resonance mode is dominant. The classical model was compared to a simplified quantum mechanical model which suggested that quantum mechanical effects become significant when the characteristic size is less than ~8 nm. Overall, we find that the analytical models are not accurate for these heterostructured semiconductor nanocrystals, indicating the need for new model development for this emerging field.

Tuning and Locking the Localized Surface Plasmon Resonances of CuS (Covellite) Nanocrystals by an Amorphous CuPdxS Shell

“…We implemented a core–shell approach within the framework of the Mie–Gans theory describing oblate particles (see the Supporting Information for details). 48 The core dielectric function of CuS was obtained by fitting the extinction spectrum of the parent CuS nanodisk sample ( d = 19.5 nm, and h = 5.5 nm) with the Drude model and by extracting the Drude parameters (see Figure S13). The estimated high-frequency dielectric constant (ε ∞ = 8.4), the plasmon frequency (ω p = 5.3 eV), and the damping constant (γ = 0.3 eV) are in close agreement with previous works on covellite CuS.…”

Cu2S/ZnS Heterostructured Nanorods: Cation Exchange vs. Solution–Liquid–Solid‐like Growth

“…[29][30][31] Partial cation exchange has also been employed to convert Cu 2Àx S NCs to alloys or heterostructures. [21,[32][33][34][35] In addition to cation exchange, epitaxial seeded growth or catalytic SLS-likeg rowth can occur,u sually leading to an augmentation of as econdary phase. [12,14,17,19,20,22,23,36] SLS growth occurs due to the supersaturationo ft he catalysts, leading to the precipitation of as econd phase in a1 Dm anner with the diameter determined by the catalysts ize.…”

“…In fact, cation exchange has become a common strategy for converting well‐established Cd‐based II–VI semiconductor NCs of various shapes to Zn‐based equivalents, with Cu 2− x S acting as the intermediate, often with the original anion lattice framework and thus the morphology of the NCs intact . Partial cation exchange has also been employed to convert Cu 2− x S NCs to alloys or heterostructures . In addition to cation exchange, epitaxial seeded growth or catalytic SLS‐like growth can occur, usually leading to an augmentation of a secondary phase .…”

Solid–Solid Phase Transformations Induced through Cation Exchange and Strain in 2D Heterostructured Copper Sulfide Nanocrystals

“…We have recently developed an analytical model in an attempt to replicate the LSPR shifts for these heterostructures. 53 In this study, we demonstrated the synthesis of dualinterface, heterostructured NCs through cation exchange. The heterostructure consists of a copper sulfide layer capped with zinc sulfide grains in spherical NCs and can be tuned by controlling the extent of the cation exchange reaction.…”