Ripening of Semiconductor Nanoplatelets

Abstract

Ostwald ripening describes how the size distribution of colloidal particles evolves with time due to thermodynamic driving forces. Typically, small particles shrink and provide material to larger particles, which leads to size defocusing. Semiconductor nanoplatelets, thin quasi-two-dimensional (2D) particles with thicknesses of only a few atomic layers but larger lateral dimensions, offer a unique system to investigate this phenomenon. Experiments show that the distribution of nanoplatelet thicknesses does not defocus during ripening, but instead jumps sequentially from m to (m + 1) monolayers, allowing precise thickness control. We investigate how this counterintuitive process occurs in CdSe nanoplatelets. We develop a microscopic model that treats the kinetics and thermodynamics of attachment and detachment of monomers as a function of their concentration. We then simulate the growth process from nucleation through ripening. For a given thickness, we observe Ostwald ripening in the lateral direction, but none perpendicular. Thicker populations arise instead from nuclei that capture material from thinner nanoplatelets as they dissolve laterally. Optical experiments that attempt to track the thickness and lateral extent of nanoplatelets during ripening appear consistent with these conclusions. Understanding such effects can lead to better synthetic control, enabling further exploration of quasi-2D nanomaterials.

Solution‐Phase Synthesis of Few‐Layer Hexagonal Antimonene Nanosheets via Anisotropic Growth

“…[5] However, practical application of antimonene is currently limited, [6] largely due to the lack of effective methods for preparing high-quality antimonene on al arge scale.T od ate,o nly af ew studies describe the successful production of antimonene nanosheets through epitaxial growth, exfoliation with av iscoelastic stamp, mechanical isolation, or straightforward liquid-phase exfoliation of Sb crystals. [8] Solution-phase synthetic methods have various advantages,including simple procedures,and the products are often easily tunable in terms of size,composition, and monodispersity,thus providing awide range of nanostructures,even nonlayered two-dimensional nanomaterials.F or example,P d, [9] CdSe, [10] and CsPbBr 3 [11] nanosheets with two-dimensional morphology have been successfully prepared using colloidal approaches,a nd these methods also have been employed to control the size and thickness of TMD materials. [8] Solution-phase synthetic methods have various advantages,including simple procedures,and the products are often easily tunable in terms of size,composition, and monodispersity,thus providing awide range of nanostructures,even nonlayered two-dimensional nanomaterials.F or example,P d, [9] CdSe, [10] and CsPbBr 3 [11] nanosheets with two-dimensional morphology have been successfully prepared using colloidal approaches,a nd these methods also have been employed to control the size and thickness of TMD materials.…”

“…[7] Unfortunately,t hese methods are not suitable for large-scale controllable preparation of 2D antimonene materials,o ri ncapable of controlling the shape, lateral size,a nd number of layers,a sw ell as the surface functionalization. [8] Solution-phase synthetic methods have various advantages,including simple procedures,and the products are often easily tunable in terms of size,composition, and monodispersity,thus providing awide range of nanostructures,even nonlayered two-dimensional nanomaterials.F or example,P d, [9] CdSe, [10] and CsPbBr 3[11] nanosheets with two-dimensional morphology have been successfully prepared using colloidal approaches,a nd these methods also have been employed to control the size and thickness of TMD materials. [3f-h] To date, the synthesis of few-layer antimonene nanosheets via this method has not been reported, even though it could potentially achieve the controllable preparation of 2D antimonene nanosheets in the solution phase.Herein, we demonstrate ac olloidal methodology for the preparation of few-layer hexagonal and functionalized antimonene nanosheets for the first time by promoting their anisotropic growth.…”

“…[7] Unfortunately,t hese methods are not suitable for large-scale controllable preparation of 2D antimonene materials,o ri ncapable of controlling the shape, lateral size,a nd number of layers,a sw ell as the surface functionalization. [8] Solution-phase synthetic methods have various advantages,including simple procedures,and the products are often easily tunable in terms of size,composition, and monodispersity,thus providing awide range of nanostructures,even nonlayered two-dimensional nanomaterials.F or example,P d, [9] CdSe, [10] and CsPbBr 3…”

Identifying reactive organo-selenium precursors in the synthesis of CdSe nanoplatelets

“…Hence, in all three syntheses, 3 ML NPLs are expected to appear early but disappear due to Ostwald ripening as the reaction proceeds. 28 The released [CdSe] monomers can redeposit either on other 3 ML NPLs (Ostwald ripening within a thickness population) or on thermodynamically more stable 4 ML NPL seeds or QDs. In the synthesis with 1, in which very little 4 ML NPLs or QDs are available, mainly lateral Ostwald ripening within a thickness population is observed.…”

“…In the synthesis with 1, in which very little 4 ML NPLs or QDs are available, mainly lateral Ostwald ripening within a thickness population is observed. 28 However, in the synthesis with 2, 4 ML NPL seeds are present in sufficient quantities that the monomers mainly deposit on them, leading after 9 min predominantly to 4 ML NPLs. In the synthesis with 3, even though 4 ML NPL seeds are present, QDs are the most abundant species.…”