Numerical study of the optoelectronic and thermoplasmonic properties of core-shell CuS@M nanoparticles (M = Au, Ag, Cu): Efficiency in near-field enhancement and photothermal conversion.

Core-shell covellite@noble metal nanoparticles (NPs) have attracted increasing interest due to their remarkable optoelectronic and photocatalytic properties. Covellite (CuS), a semiconducting metal chalcogenide, is a promising core material for various applications such as pollutant degradation and photothermal therapy. Its combination with a noble metal shell enables the exploitation of surface plasmon resonance (SPR), thereby enhancing light absorption and opening the way to advanced photocatalytic and biomedical applications. However, previous studies on CuS, based core-shell nanostructures have generally been limited to a single noble metal shell, most often Au (e.g., Au@Cu₂S, Au@CuS) or, less frequently, Ag (e.g., CuS@Ag), leaving the direct, systematic comparison of different metallic shells on the same CuS core largely unexplored. In this work, the plasmonic properties as well as the performance associated with this phenomenon of CuS@M (M = Au, Ag, or Cu) core/shell NPs were investigated, such as the near-field enhancement efficiency and photothermal conversion. First, density functional theory (DFT) was employed to determine the optoelectronics properties of CuS. Then, the finite element method (FEM) was applied to analyze the plasmonics properties of CuS@M NPs. In this context, the parameters characterizing SPR, such as absorption and the near-field distribution under light excitation, were evaluated. Subsequently, thermoplasmonic performance (Joule number J0) and field enhancement (Faraday number Fa) were analyzed as functions of the NPs' geometrical parameters. The results show that CuS@Au and CuS@Cu NPs exhibit a single SPR peak, whose position mainly depends on the core radius: for CuS@Au, the SPR peak shifts from 524 nm to 1055 nm, while for CuS@Cu it shifts from 566 nm to 1044 nm. For CuS@Ag, increasing the CuS-core radius leads to the appearance of a second peak in the UV-Vis band, together with a redshift of the first peak. Moreover, the SPR field enhancement and light-to-heat conversion efficiency can be tuned by adjusting the shell thickness and the nature of the metal used. These results thus open the way to nanomedical applications, particularly in biomedical diagnostics, optical imaging, and targeted photothermal therapy, as well as to photocatalytic applications such as environmental remediation and pollutant degradation.