Two-dimensional colloidal nanoplatelets (NPLs) with atomically defined thickness exhibit unique physical properties, yet understanding their formation mechanism and assembly remains essential for tuning their collective behavior. We report an optimized synthesis of triangular cerium-based NPLs with narrow size and shape distributions via thermal decomposition of cerium trifluoroacetate. Combining X-ray diffraction, XPS, and high-resolution STEM, we show that the expected CeF3 NPL structure undergoes partial oxidation, yielding an oxyfluoride composition CeOxFy. Beyond their composition, we investigate how these oleic acid-capped NPLs organize in solution and at interfaces. The choice of solvent governs both the solution-phase organization and the resulting superstructures formed upon evaporation at the liquid–air interface. In solvents that promote face-to-face stacking in solution, evaporation produces films organized into columnar assemblies tens of micrometers long, with the NPL planes oriented perpendicular to the interface. In contrast, solvents in which NPLs remain individually dispersed yield extended hexagonally ordered superlattices with edge-to-edge stacking spanning several micrometers, where the NPLs lie parallel to the interface in an edge-to-edge arrangement. These results highlight that solvent-mediated interactions and pre-existing organization in solution are decisive factors in determining the outcome of evaporative self-assembly of colloidal nanocrystals.

Achieving controlled and directed motion of artificial nanoscale systems in three-dimensional fluid environments remains a key-challenge in active matter, primarily due to the prevailing thermal fluctuations that rapidly randomize the particle trajectories. While significant progress has been made with micrometer-sized particles, imparting sufficient mechanical energy, or self-propulsion, to nanometer-sized particles to overcome Brownian diffusion and enable controlled transport remains a major issue for emerging applications in nanoscience and nanomedicine. Here, we address this challenge by demonstrating the fuel-free, reversible, and tunable active behavior of gold-silica (Au-SiO2) Janus nanoparticles (radius R ∼ 33 nm) induced by optical excitation. Using single particle tracking, we provide direct experimental evidence of self-thermophoresis, clearly distinguishing active motion from thermal noise. These light-driven Janus nanoparticles constitute a minimal yet robust photothermal system for investigating active matter and its manipulation at the nanoscale.

We report a drastic difference in stacking behavior of oleic acid-stabilized 4-monolayer (4 ML) CdSe nanoplatelets (NPLs) in toluene and methylcyclohexane (MCH), two nonpolar solvents that differ in the conformational flexibility of their molecules. Using liquid cell transmission electron microscopy (TEM) and small angle scattering (SAXS) techniques, we show that NPLs form microns-long ribbons consisting of 4 ML CdSe NPLs in toluene, the solvent widely used to form stable colloidal solutions of a broad range of quasi-spherical nanoparticles. In contrast, 4 ML CdSe NPLs are well dispersed in MCH. The difference in stacking behavior of NPLs in toluene and MCH suggests that the conformational flexibility of the solvent molecules, such as the ability to adopt multiple chair conformations, modulates nanoplatelet interactions. Molecular dynamics (MD) simulations reveal that solvent molecules subtly alter the structure of the organic ligand shell. These solvent-dependent changes propagate to the inorganic core, modulating the degree of CdSe nanoplatelet (NPL) twisting and, consequently, the properties of the nanoparticles. We show that toluene better solvates oleate ligands while MCH induces a bimodal oleate span distribution, which can lead to increased solubility of CdSe NPLs. In addition, the solvent can also influence the inorganic core, which, in turn, can modify the nanoparticle properties. We demonstrate that destabilization of toluene solution containing ribbons of 4 ML CdSe NPLs without CdS shells results in the formation of NPL assemblies with amplified spontaneous emission (ASE) with a low threshold of 14 µJ cm-2 that is comparable with that of CdSe/CdS core/shell NPLs. Our results emphasize that the solvent plays a major role in mediating interactions between NPLs and hence their processability for fabrication of functional structures.

Core-crown CdSe/CdS nanoplatelets combine improved quantum yield with promising optoelectronic performance, yet their emission dynamics remain governed by reversible charge trapping. By correlating single-particle luminescence decays with intensity fluctuations (blinking/flickering), we uncover a distinct emission regime at intermediate brightness levels where delayed luminescence arises. This behavior reflects a reversible trapping process that reduces light emission and introduces a secondary, slow decay channel. Time-resolved analysis reveals stochastic switching between active and inactive reversible trapping within an individual emitter. Under higher excitation powers, these reversible traps are supplanted by stronger nonradiative quenching pathways.

Colloidal CdSe nanoplatelets (NPLs) are promising materials for various applications due to their unique optical properties arising from their atomically controlled thickness. However, the lack of understanding of their formation mechanism can result in low yields, multiple side products that are hard to separate, and unknown ligand compositions on their surface. All of these factors hinder the development and exploitation of such nanocrystals in devices. Herein, we focused on assessing the effect of long-chain cadmium(II) carboxylate (oleate and myristate) preparation methods on NPL synthesis. While cadmium(II) myristate always crystallizes in a lamellar structure irrespective of its preparation pathway, we show that cadmium(II) oleate displays two structures, one amorphous and one lamellar, that coexist in different relative concentrations depending on the synthesis method used to prepare the precursor. These differences impact the NPL synthesis through the precursor dissolution rate, which varies according to the supramolecular structure. The lamellar structure dissolves faster and yields a thinner NPL population than the amorphous one.

Seed-mediated synthesis of nanoparticles typically results in hetero-epitaxial growth, which eventually leads to larger nanoparticles with core-shell morphology. Counter intuitively, a seed-mediated glycothermal synthesis of large-lanthanide gallium/aluminum garnets nanoparticles (NPs) (Ln3(Ga/Al)5O12, Ln = Lanthanide, e.g., Tb/Gd/Eu) using undoped YAG (Yttrium Aluminum Garnet, Y3Al5O12) NPs as seeds, yielded highly dispersed colloidal garnets NPs of interest with no discernible core-shell features. Moreover, most of them are physically separate from the seeds. Based on the time-dependent evolution of physico-chemical and optical characterizations of the materials during reaction, along with DFT modeling, we offer a first insight into the mechanistic aspects of this non epitaxial NP formation. Growth of an amorphous Ln-(Al/Ga)-based material on top of the seed ligand is predicted computationally and confirmed experimentally, followed by detachment of the garnet NPs of interest away from the ligand-protected seeds once garnet crystallization occurs. This novel mechanism could be leveraged to overcome high formation barriers and enable seed-mediated synthesis of colloidal garnet nanoparticles with large lanthanides, or even beyond, without core-shell structure.

The ability of thin materials to shape-shift is a common occurrence that leads to dynamic pattern formation and function in natural and man-made structures. However, harnessing this concept to design inorganic structures at the nanoscale rationally has remained far from reach due to a lack of fundamental understanding of the essential physical components. Here, we show that the interaction between organic ligands and the nanocrystal surface is responsible for the full range of chiral shapes seen in colloidal nanoplatelets. The adsorption of ligands results in incompatible curvatures on the top and bottom surfaces of NPL, causing them to deform into helico\"ids, helical ribbons, or tubes depending on the lateral dimensions and crystallographic orientation of the NPL. We demonstrate that nanoplatelets belong to the broad class of geometrically frustrated assemblies and exhibit one of their hallmark features: a transition between helico\"ids and helical ribbons at a critical width. The effective curvature $\bar{\kappa}$ is the single aggregate parameter that encodes the details of the ligand/surface interaction, determining the nanoplatelets' geometry for a given width and crystallographic orientation. The conceptual framework described here will aid the rational design of dynamic, chiral nanostructures with high fundamental and practical relevance.

We report the conformational control of 2D ultra-thin indium sulfide nanoribbons by tuning their amine ligands' alkyl chain. The initial orthorhombic InS nanoribbons bare octylamine ligands and display a highly curved geometry with a characteristic figure of eight shapes. Exchanging the native ligand by oleylamine induces their complete unfolding to yield flat board-shaped nanoribbons. Significant strain variations in the InS crystal structure accompany this shape-shifting. By tuning the linear alkyl chain length from 4 to 18 carbon atoms, we show using SAXS in solution and TEM that the curvature of the nanoribbon subtly depends on the ligand-ligand interactions at the nanoribbon's surface. The curvature decreases gradually as the chain length increases, while carbon unsaturation has an unexpectedly significant effect at constant chain length. These experiments shed light on the critical role of the ligand monolayer on the curvature of ultrathin 2D crystalline nanosheets and demonstrate that weak supramolecular forces within the organic part of colloidal nanocrystals can dramatically impact their shape. This transduction mechanism, in which changes in the organic monolayer impact the shape of a nanocrystal, will help devise new strategies to design stimuli-responsive systems that take advantage of both the flexibility of organic moieties and the physical properties of the inorganic core.

Metallogels built in a bottom-up approach by metal coordination and supramolecular interactions have important potential for the elaboration of smart materials. In this context, we present here the formation of supramolecular coordination polymers driven by the complexation of cobalt(II) or zinc(II) ions with polyoxometalate-based hybrids displaying two terpyridine ligands in a linear arrangement. Thanks to the electrostatic interactions between the polyoxometalate cores and metal nodes, the polymer chains self-assemble into fibers that physically cross-link to form gels above a critical concentration. Using spectroscopy, microscopy, X-ray scattering, and rheometry, complemented by molecular dynamics simulations, we investigated the supramolecular organization of the chains in the fibers and the resulting processes leading to gelation. Compared to previously reported systems, these gels have improved rheological features and appealing properties, such as birefringence, luminescence, and spin crossover, paving the way for their use as building blocks for multifunctional smart materials.

Inducing chirality in semiconductor nanoparticles is a recent trend motivated by the possible applications in circularly polarized light emission, spintronics, or stereoselective synthesis. However, the previous reports on CdSe nanoplatelets (NPLs) exclusively rely on cysteine or its derivatives as chiral ligands to induce optical activity. Here, we show a strong induction of chirality with derivatives of tartaric acid obtained by a single-step synthesis. The ligand exchange procedure in organic solvent was optimized for five-monolayer (5 ML) NPLs but can also be performed on 4, 3, and 2 ML. We show that the features of the CD spectra change with structural modification of the ligands and that these chiral ligands interact mainly with the first light-hole (lh1) band rather than the first heavy-hole (hh1) band, contrary to cysteine. This result suggests that chiroptical properties could be used to probe CdSe nanoplatelets' surface ligands.

We report the two-dimensional self-assembly at the liquid-air interface of spherical gold nanoparticles (NPs) with diameters between 2 and 14 nm. By exploring the self-assembly conditions, such as the dispersing solvent and the coating ligand (thiols with different lengths, oleylamine, polystyrene), we identify suitable conditions for long range close-packed monolayers obtention. We show that though NPs with diameters below 3 nm yield glassy films or fuse during self-assembly depending on the ligand length, NPs with larger sizes dispersed in toluene yield well-ordered monolayers over distances that can span tens of micrometers. Adding free ligand in solution before the self-assembly triggers long range ordering into close-packed structures of otherwise amorphous films. The equilibrium distance between the NPs within the monolayers are compared to predictions by the OPM and OCM geometrical models. We also observed a CaCu5 phase in few-layers assemblies which results from the size segregation of a single monodisperse population of NPs into two populations of different mean sizes occupying the two different sites of this complex lattice. In some instances, Moiré patterns consisting of two close-packed hexagonal monolayers superimposed with a twist angle are evidenced. By comparing the experimental structures with numerically simulated patterns, we show that a twist angle of 30° yields a quasicrystalline order with a 12-fold rotational symmetry. Our work provides insights into fundamental processes behind the self-assembly of colloidal nanocrystals into ordered mono- and few-layers as well as more complex assemblies such as quasicrystalline or Frank-Kasper phases. These structures are of great significance for bottom-up fabrication of functional devices that advantage of (collective) plasmonics properties or surface enhanced raman scattering.

One can nowadays readily generate monodisperse colloidal nanocrystals, but the underlying mechanism of nucleation and growth is still a matter of intense debate. Here, we combine X-ray pair distribution function (PDF) analysis, small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM) to investigate the nucleation and growth of zirconia nanocrystals from zirconium chloride and zirconium isopropoxide at 340 °C, in the presence of surfactant. We find that initially, many amorphous particles are formed. Over time, the total particle concentration decreases while the amorphous particles recrystallize into ZrO2 nanocrystals. After a sudden increase, the concentration of nanocrystals stays constant over the course of the reaction. Both findings stand in contrast to reports of continuous nucleation in other surfactant-assisted nanocrystal syntheses. The non-classical nucleation is likely related to the precursor decomposition rate that is an order of magnitude higher than the observed crystallization rate. Comparing different zirconium precursors, we observe higher smaller particles for reactions with ZrBr4 or with Zr(OtBu)4, which we could correlate with a higher precursor decomposition rate.

Heterostructured cadmium-based core–shell nanoparticles (NPs) are the subject of research because of not only fundamental scientific advances but also a range of technological applications.

We use micro-photoluminescence to demonstrate collective blinking of self-assembled stacks of around 70 semiconducting nanoplatelets. This effect is explained and modelled as Förster-resonant energy tranfer (FRET) funneling all the excitons from a chain portion to a single blinking quencher.

The difference between in-plane and out-of-plane bonding energy of transition metal dichalcogenides has provided the possibility of isolating single layers. A one step synthesis protocol to produce size-controlled single layers has always been challenging. Here we developed a new colloidal synthesis to produce monodisperse size-controlled 1T'-WS2 nano-monolayers with outstanding colloidal stability by using 1-octadecanethiol as the coordinating agent. Changes in the reaction time and amount of coordinating agent regulate the mean size of the nanosheets. We investigated the effect of octadecanethiol and injection rate on the dispersion and mean-size, using UV-Vis spectroscopy, X-ray diffraction techniques, and transmission electron microscopy. Furthermore, thermogravimetric analysis and Fourier transform infrared spectroscopy allow for ligands detection and analysis at the surface of the nanosheets. These results open a new pathway to synthesize, control and explore the properties of nanoscale transition metal dichalcogenides.

Self-assembled linear chains of CdSe nanoplatelets are known to exhibit highly efficient Förster resonant energy transfer (FRET) leading to fast exciton diffusion between platelets. Here, we compare the luminescence decay dynamics of single nanoplatelets, clusters of a few platelets, and self-assembled chains. As the number of stacked platelets is increased, we show that the luminescence decay becomes faster, which can be interpreted as the FRET-mediated effect of quenchers: excitons may diffuse to nearby quenchers so that their decay rate is increased. On the other hand, a minor slow decay component is also observed for single platelets, corresponding to trapping-detrapping mechanisms in nearby trap states. The contribution of the slow component is enhanced for the platelet chains. This is consistent with a FRET-mediated trapping mechanism where the excitons would diffuse from platelet to platelet until they reach a trap state. Finally, we develop toy models for the FRET-mediated quenching and trapping effects on the decay curves and analyze the relevant parameters.

In situ X-ray scattering kinetics and population balance modeling of crystal nucleation and growth.

Chiral halide perovskite nanocrystals have many applications in next-generation optoelectronic devices due to their interaction with circularly polarized light. Through the careful selection of chiral organic surface ligands, control over the circular dichroism (CD) and circularly polarized luminescence (CPL) of these materials can be achieved. However, while recent developments of CD-active perovskites have seen significant advances, effective CPL remains a challenge. Here, we synthesize colloidal perovskite nanoplatelets exhibiting room temperature CPL with dissymmetry factors up to glum=4.3×10^(-3) and gabs=8.4×10^(-3). Methylammonium lead bromide nanoplatelets are synthesized with a mixture of chiral dimethyl benzyl ammonium ligands and achiral octylammonium ligands, the precise ratio of which is shown to be critical to achieving high g-factors. We investigate the competitive binding of these surface ligands using 1H NMR, and use an equilibrium model to demonstrate the ligand affinity. The magnitude of CPL and CD is quantitatively shown to exhibit a linear correlation, such that glum=0.4×gabs. Lastly, by screening several amines with close structures, we show that subtle differences in ligand structure have significant impact on the resulting CD signal of the nanoplatelets. Our findings provide new insights for the effective design of perovskites exhibiting CPL and can facilitate the development of high-performance devices based on circularly polarized luminescence.