Controllable Transformation from Rhombohedral Cu_1.8S Nanocrystals to Hexagonal CuS Clusters: Phase- and Composition-Dependent Plasmonic Properties

Abstract

Because of the rich polymorphs and lower diffusion energy barriers of copper chalcogenide systems, the phase transformation of colloidal Cu2–x S (0 ≤ x ≤ 1) nanocrystals is critical for understanding their fundamental properties and designing convenient synthetic routes. In this work, high quality digenite Cu1.8S nanocrystals with rhombohedral structure were synthesized at gram-scale. The as-prepared colloidal nanocrystals undergo an in situ phase transformation from rhombohedral Cu1.8S nanocrystals to hexagonal CuS clusters upon keeping the resulting colloidal solution for a few days. The observed transformation was explored by a combination of structural and spectroscopic analyses, including powder X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy characterizations. A possible mechanism is proposed and thoroughly discussed. We further determined the evolution of plasmonic absorption spectra during the transformation. The Cu1.8S nanocrystals and CuS clusters exhibit composition-dependent local surface plasmon resonance absorption (LSPR) in the near-infrared region, which are in good agreement with calculated extinction spectra based on Mie-Drude model. Combined experimental and theoretical analyses demonstrated that both the phase induced dielectric constant change and the composition induced carrier concentration variation account for the spectroscopic evolution.

Synthesis and characterization of hexagonal faceted copper sulfide (Cu1.8S) nanodisks

“…1. The obtained XRD pattern matches well with the JCPDS file 1 15) and (2 0 20) respectively [26]. There are no secondary peaks from other phases of Cu 2 À x S or any other impurity peaks could be detected from the XRD analysis.…”

Salt‐Assisted Growth of P‐type Cu9S5 Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

“…Basically, the field effect transistor (FET) change carrier density and thus the channel conductance by creating a surface inversion layer 9a. The maximum induced space charge width, which marks the maximum thickness of a device that could be effectively turned off, can be calculated as follows where ε s is the permittivity of the Cu 9 S 5 (2.6* 8.85* 10 −14 ), V t is (0.0259), N a is the doping density of Cu 9 S 5 (10 20 ), n i is the intrinsic carrier concentration and can be estimated to be 10 6 –10 8 . Consequently, X d can be calculated to be ≈2.1 nm.…”

Structural evolution from CuS nanoflowers to Cu9S5 nanosheets and their applications in environmental pollution removal and photothermal conversion

“…11 As a type of important plasmonic semiconductor, copper chalcogenide provides an alternative plateform for PTA removal of tumor cells in cancer therapy because of their controllable absorption in the NIR spectrum, low-cost fabrication, and acceptable cytotoxicity. For example, several polymorphs of nonstoichiometric Cu 2-x S compounds including Cu 2 S (chalcocite), Cu 1.94 S (djurleite), Cu 1.8 S (digenite), Cu 1.75 S (anilite) and CuS (covellite) are p-type semiconductors and exhibit a stoichiometry-dependent band gap 30,31 size-, geometry-, and phase-, dependence of LSPR related absorption properties in Cu 2-x Y nanocrystals have also been extensively investigated besides composition. For example, several polymorphs of nonstoichiometric Cu 2-x S compounds including Cu 2 S (chalcocite), Cu 1.94 S (djurleite), Cu 1.8 S (digenite), Cu 1.75 S (anilite) and CuS (covellite) are p-type semiconductors and exhibit a stoichiometry-dependent band gap 30,31 size-, geometry-, and phase-, dependence of LSPR related absorption properties in Cu 2-x Y nanocrystals have also been extensively investigated besides composition.…”

“…52 The LSPR behaviors of the plasmonic semiconductor copper chalcogenide nanocrystals have been investigated experimentally and theoretically. 53,54 However, it is still a challenge to understand of structure-to-property relations and control the nanocrystal morphologies, especially the nanostructure with secondary structures. For example, mesoporous anatase-silica nanocomposites with secondary mesopores exihibited the superhigh photocatalytic degradation of Rhodamine B, Acid Red, microcystin-LR compared to counterpart without secondary mesopores.…”