In Situ Probing of Stack-Templated Growth of Ultrathin Cu_2–xS Nanosheets

Abstract

Ultrathin two-dimensional (2D) nanomaterials have attracted intense research efforts due to their extraordinary optoelectronic properties. However, the nucleation and growth mechanisms of 2D colloidal nanosheets are still poorly understood. Here, we follow the formation of ultrathin colloidal Cu2–x S nanosheets by in situ small-angle X-ray scattering. While thermal decomposition of copper–dodecanethiolates produces spheroidal Cu2–xS nanocrystals, the addition of chloride to the reaction mixture results in 2 nm thick Cu 2–x S nanosheets with well-defined shape and size. Our results show that chloride stabilizes stacks of lamellar copper–thiolate supramolecular complexes, so that they remain intact beyond the onset of Cu2–x S nucleation at 230 °C, leading to 2D-constrained stack-templated nucleation and growth. The face-to-face stacking of the nanosheets reinforces the 2D constraints imposed by the lamellar soft template, since it prevents internanosheet mass transport and nanosheet coalescence, thereby inhibiting growth in the thickness direction and allowing only for lateral growth. Our work thus provides novel insights into soft-templating formation mechanisms of ultrathin colloidal nanosheets, which may be exploited for other metal sulfide compositions.

Shape Control of Colloidal Cu2–xS Polyhedral Nanocrystals by Tuning the Nucleation Rates

“…Our group has previously reported that the addition of SnBr 4 to synthesis protocols for Cu 2– x S NCs dramatically affects the size and shape of the product NCs, yielding ultrathin (2 nm thick) Cu 2– x S nanosheets with well-defined shape and size (triangular or hexagonal; 100 nm to 3 μm wide) instead of nearly spherical small (9 nm diameter) NCs. 29 , 43 The effect was clearly shown to be due to the halides, such that Sn(IV) tetrahalides were only relevant as sources of sufficiently high halide concentrations in the growth solution. 29 , 43 To investigate the roles of the halide and Sn(IV) in the present case, we carried out control experiments in which either SnBr 4 was replaced by Sn(OAc) 4 or additional halides were added in the form of CuBr in the absence of any Sn(IV) compound.…”

Ultrathin One- and Two-Dimensional Colloidal Semiconductor Nanocrystals: Pushing Quantum Confinement to the Limit

“… 16 , 26 A soft-template mechanism has also been proposed to explain the formation of Cu 2– x S NSs by 2D-constrained nucleation and growth within halide-stabilized lamellar Cu-thiolate complexes. 57 This mechanism was supported by in situ SAXS studies, which clearly demonstrated that chloride ions present in the growth medium stabilize stacks of lamellar Cu-thiolate complexes, ensuring their structural integrity beyond the onset of Cu 2– x S nucleation. 57 Therefore, the thermolysis of the C–S bonds leads to 2D-constrained stack-templated nucleation and growth of Cu 2– x S NSs.…”

“… 57 Therefore, the thermolysis of the C–S bonds leads to 2D-constrained stack-templated nucleation and growth of Cu 2– x S NSs. 57 …”

“…For example, the addition of halides (chloride or bromide) has been shown to increase the thermal stability of 2D lamellar Cu-thiolate templates, preserving their structural integrity beyond the onset of Cu 2– x S nucleation, thereby leading to 2D-constrained nucleation and growth of Cu 2– x S NSs. 57 We propose that, if the electrostatic interactions are dipolar in nature, the thermally induced collapse of the 2D templates will lead to 1D templates that are likely stabilized by both dipolar interactions between the building blocks (MSCs or NCs) and van der Waals interactions between densely packed ligands organized in a tubular array in which the polar heads face inward ( Figure 8 ). Further increase of the reaction temperature will also destabilize the 1D template and will lead to 3D growth of NCs.…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…The demicellization involved a two-step process of the fast release of unimers followed by slower disintegration. A combination of SAXS and USAXS allowed the elucidation of the mechanism underlying the formation of ultrathin (∼2 nm) colloidal Cu 2−x S nanosheets with well-defined shape and size [95]. The thermal decomposition of copper-dodecanethiolates usually leads to spheroidal Cu 2−x S nanocrystals, but chloride stabilization of the stacks of lamellar copper-thiolate supramolecular complexes led to 2D-constrained stack-templated nucleation and growth, in which growth in the thickness direction is inhibited (allowing only the lateral growth).…”