Computation-Motivated Design of Ternary Plasmonic\nCopper Chalcogenide Nanocrystals

Abstract

Nanocrystals\ncomposed of copper­(II) sulfide (CuS), a degenerately\ndoped semiconductor with a direct optical bandgap, have been observed\nto exhibit both visible wavelength excitonic emission and strong localized\nsurface plasmon resonances (LSPRs) in the near-infrared, making them\nprime candidates for exploring phenomena such as coupled light–matter\ninteractions, quantum entanglement, and optical nonlinearity. Here,\nwe report a computation-motivated synthetic approach for modulating\nthe optical bandgap energy of plasmonic nanocrystals relative to their\nLSPR energies by tuning the composition of alloyed CuSe<i>_x</i>S_1–<i>x</i> nanocrystals.\nCuSe<i>_x</i>S_1–<i>x</i> alloys are examined by first-principles density functional\ntheory (DFT) to understand the effects of composition tuning on the\nelectronic and optical properties of CuSe<i>_x</i>S_1–<i>x</i>, using high-throughput methods\nto probe Se occupation within a parent CuS unit cell. Results from\nthis DFT analysis are used as input parameters for predicting the\nLSPR of CuSe<i>_x</i>S_1–<i>x</i> nanostructures. To validate these DFT results against experimental\nobservations, we synthesize CuSe<i>_x</i>S_1–<i>x</i> using CuS nanodisks as a template\nfor a novel anion-exchange protocol. Optical characterization reveals\nqualitative agreement between our experimental and predicted materials\nproperties, and we discuss how quantitative deviations from our predicted\nvalues are likely the result of interfacial and morphological characteristics\nthat are unaccounted for in DFT models.