Covellite Nanodisks and Digenite Nanorings: Colloidal Synthesis, Phase Transitions, and Optical Properties

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Chemistry and Biochemistry


Mathematics and Natural Sciences


Copper sulfide nanoparticles represent a class of dual-functional materials whose optical properties are dominated by interband electronic transitions and intraband plasmon resonances, both of which can be systematically tuned by tailoring the geometric parameters and chemical compositions of the nanoparticles. Here, we report a temperature-programmed synthetic approach to monolithic covellite (CuS) nanodisks with thicknesses of around 11 nm and lateral diameters widely tunable in the range of ∼100–300 nm. Our synthetic approach expands the aspect ratio-tuning range of covellite nanodisks typically achievable through previously developed colloidal syntheses, thereby enabling us to extend the plasmonic tunability of covellite nanodisks across near-infrared deep into mid-infrared. Covellite nanodisks with even larger lateral diameters beyond 300 nm, each of which is composed of stacked monolithic layers, can be synthesized either by increasing precursor concentrations or through seed-mediated nanodisk overgrowth. The superimposition of horizontally twisted covellite lattices in stacked monolithic layers gives rise to the emergence of Moiré patterns on individual nanodisks in transmission electron microscopy images. Upon thermal treatment, monolithic covellite nanodisks dispersed in tetraethylene glycol transform into multicrystalline digenite (Cu1.8S) nanorings through a postsynthesis phase-transitioning process, which not only further modifies plasmonic properties but also leads to energy shifts of the band gap and Fermi level of the nanoparticles. As revealed by the results of correlated atomic force microscopy and Kelvin probe force microscopy measurements, the local surface work functions of the covellite nanodisks and digenite nanorings in the size regime investigated in this work are essentially independent of the local surface topographic features and the way in which the quasi-two-dimensional nanostructures are stacked.

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Chemistry of Materials





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