Scroll-like colloidal quasi-two-dimensional CdS x Se1–x nanoplatelets (NPLs) with a thickness of five monolayers and average lateral dimensions of 100 nm over the whole composition range (0 ≤ x ≤ 1) were synthesized by using a mixture of chalcogenide precursors. According to X-ray diffraction and X-ray energy dispersive spectroscopy mapping in a scanning transmission electron microscope, as-synthesized NPLs are solid solutions with a uniform elemental distribution in each individual nanoplatelet. A change in composition leads to the continuous shift and gradual broadening of exciton absorption and photoluminescence (PL) lines in the visible blue and near-ultraviolet light range. Detailed analysis of optical properties, including temperature-dependent PL spectroscopy, revealed the nonmonotonic behavior of several optical parameters (average phonon temperature, electron–phonon interaction coefficient, and Stokes shift) starting from a sulfur content of ∼40% in alloyed NPLs. This behavior may be attributed to the local composition fluctuations within CdS x Se1–x solid solution nanoplatelets.

Colloidal two-dimensional cadmium chalcogenides nanoplatelets have recently emerged as a class of semiconductor nanoparticles with the narrowest emission and absorption excitonic bands that are of interest for optical applications. Here, we have developed a synthesis protocol for 2.5-monolayer-(ML) thick CdSe nanosheets as a single population. We found that a two-step synthesis in the presence of water promoted the growth of atomically thin nanosheets with high structural and morphological perfection. Using a seeded-growth technique, we extended the lateral size of nanosheets up to 400 nm, which led to the formation of multiwall rolled-up nanostructures. Ligand exchange of native oleic acid, attached to Cd-rich (001) planes, with achiral thioglycolic acid and chiral N-acetylcysteine retains a scroll-like morphology of nanosheets, in contrast to a thicker 3.5 ML population. A reorientation from the [110] to [100] folding direction was found during the change from an achiral to a chiral ligand. In the case of ligand exchange with chiral N-acetyl-l- or d-cysteine, we demonstrated that 2.5 ML CdSe nanosheets with 400 nm lateral size have circular dichroism with a dissymmetry g factor up to 3 × 10–3. Strong circular dichroism found for colloidal CdSe nanosheets makes them a promising candidate for polarization-enabled applications, while the growth protocol of the thinnest CdSe nanosheets enriches the known synthesis methods of a set of CdSe nanoplatelet populations.

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Two-dimensional (2D) semiconductors exhibit unique electronic and optical properties arising from the atomic-scale thickness and two-dimensional electronic structure. However, it is usually limited by an intrinsically flat morphology of 2D materials. Here, we report an effect of spontaneous folding of quasi-2D CdTe nanosheets stimulated by ligand exchange. We show that initially flat CdTe nanosheets with 100−200 nm lateral size and 5−6 ML thickness are uniformly rolled up when oleic acid is replaced by thiol-containing ligands. Detailed study shows nanosheet folding along the [110] direction forming multiwall scroll-like structures with the diameter being dependent on sheet thickness. A pronounced red shift of the exciton transitions of CdTe nanosheets is found due to thickness increase and strain appearance under thiol attachment. The folding mechanism is likely related to misfit strain at CdTe (001) basal planes as ultrathin CdS layer is formed. Possibility to precisely tune the nanostructure shape simply by ligand-induced strain can evolve into new synthetic strategies to control a spatial morphology of 2D materials.