Room-Temperature Synthesis of Covellite Nanoplatelets with Broadly Tunable Localized Surface Plasmon Resonance

Abstract

Preparation of nanomaterials with controllable size and shape at ambient conditions, without heating or cooling, is extremely attractive from the perspective of cost and energy efficiency. However, highly reactive precursors must be used to obtain NCs at ambient conditions, and this can make the control of particle formation extremely challenging. Degenerately p-doped copper sulfide NCs have attracted much recent interest based on the observation of localized surface plasmon resonance (LSPR) in these materials. These earth-abundant semiconductor NCs have potential applications ranging from photovoltaics to biomedical imaging. Here, we provide the first report of ambient-temperature preparation of covellite nanoplatelets. The lateral dimensions of these are controllable over a wide range while maintaining a constant thickness of 4 nm. The crystalline phase of the NCs is shown here to be controlled by the oxidation state of copper reagent, with a Cu(II) precursor required to prepare phase-pure covellite NCs. The NCs exhibit LSPR absorbance that depends upon their aspect ratio (their lateral dimension, at fixed thickness) and can be tuned over a range of more than 600 nm. Their optical absorbance was modelled quantitatively to extract consistent values of free carrier concentration and background polarizability that apply over a wide range of NC sizes.

Chemical Control of Plasmons in Metal Chalcogenide and Metal Oxide Nanostructures

“…Discrete dipole approximation (DDA) calculations suggest that the energy of the in-plane plasmon has an intensity so much smaller than the out-of-plane plasmon that the latter resonance only produces a minor, hardly recognizable feature with the large aspect ratio of the hexagonal disks. [ 27 ] Similar plasmonic absorption features have been observed by Manna et al in copper phosphide platelets [ 28 ] and by Liu et al in covellite CuS disks. [ 27 ] In these two instances, increased aspect ratios result from the in-plane surface of the particles expanding equally in all directions.…”

“…[ 27 ] Similar plasmonic absorption features have been observed by Manna et al in copper phosphide platelets [ 28 ] and by Liu et al in covellite CuS disks. [ 27 ] In these two instances, increased aspect ratios result from the in-plane surface of the particles expanding equally in all directions. However, in the Cu 2-x S discs described by Hsu et al, [ 24 ] the larger aspect ratio is a result of the particle size elongating more in one direction.…”

Phase Transformations of Copper Sulfide Nanocrystals: Towards Highly Efficient Quantum‐Dot‐Sensitized Solar Cells

“…Owingt ot he excellent opticala nd electrical properties of Cu 2Àx SN Cs, the synthesis of Cu 2Àx SN Cs with various sizes, shapes,p hases, and compositions has been intensively studied in recent years. [29][30][31][32][33][34][35][36][37][38] Here, hexagonal CuS, monoclinic Cu 1.75 S, and rhombohedral Cu 1.8 SN Cs were synthesized by ah ot-injection method;t he crystal structures of the as-synthesized CuS, Cu 1.8 S, and Cu 1.75 SN Cs have been identified by XRD and highresolution TEM in our previousw ork. [39,40] The heat-induced phase transformation of Cu 1.8 SN Cs has also been studied in Owing to their high electrical conductivity,t unable plasmonic absorption spectra, low cost, and abundancei nn ature,C u 2Àx S nanocrystalsa re of great interest as functional materials for photovoltaic and photothermal applications.…”

Plasmonic doped semiconductor nanocrystals: Properties, fabrication, applications and perspectives

“…In copper sulfide, at least five different crystal phases have been documented (see previous sections) [152,203] and the control over structure and stoichiometry can be a tool for achieving dynamic, reversible LSPR tuning. [12,136,142,152,153,204] The various crystal phases are correlated to the LSPR and the deep understanding of the influences of phase transformation on the plasmonic behavior are of major importance.…”