Ligand-Induced Incompatible Curvatures Control Ultrathin Nanoplatelet Polymorphism and Chirality

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.Comment: 16 pages, 8 figure

Nanoplaquettes à changement de forme : induction de la chiralité dans les matériaux ultraminces

Chirality is a fascinating property manifesting on all size scales in the universe. At the nanoscale, interactions between circularly polarized light and chiral matter can result in chiroptical activity. Combined with the unique optical properties of ultrathin semiconducting nanocrystals, this creates a rich playground for the creation of novel chiral materials. However, many fundamental questions remain regarding the factors influencing chirality in inorganic nanoscale materials. This thesis aims to understand how chirality can be induced in ultrathin systems. This is achieved through electronic ligand-nanocrystal coupling, and by deforming ultrathin sheets into chiral shapes. The first chapter provides an introduction to relevant scientific concepts drawn from the literature. The second chapter demonstrates large magnitudes of circular dichroism and circularly polarized luminescence in methylammonium lead bromide perovskite nanoplatelets through ligand-induced chirality. Samples are prepared using a precise mixture of chiral and nonchiral ligands to optimize chiroptical signals.3The competitive ligand binding is described using an equilibrium model, elucidating relationships between the surface ligands and chiroptical properties. The third chapter demonstrates structural chirality by controlling the conformation of helical CdSe nanoplatelets through temperature-dependent surface ligand stresses. By altering the ligand functional group and alkyl chain, the radius of curvature is changed in both magnitude and sign, resulting in nanoplatelet ``shapeshifting''. These changes are attributed to multiple factors including ligand binding configuration, ligand desorption and decomposition, and nanocrystal surface reconstruction. The fourth chapter searches for new ultrathin shapeshifting systems by understanding the interplay between surface chemistry, crystal structure, and conformation. First, patch-wise phosphonic acid ligand exchange is shown to flatten CdSe nanohelices. Other systems are explored: lead sulfide and lanthanide oxide nanoplatelets are prepared, the phase transformation of tungsten disulfide nanomonolayers is characterized, and lastly, the unrolling of indium sulfide nanocoils is demonstrated. This work advances the understanding of mechanics at the nanoscale, helping to elucidate the relationship between nanoplatelet deformation and surface-ligand stress. By uncovering the mechanisms behind ligand-induced chirality and nanoplatelet curvature, this work paves the way towards the rational design of ultrathin chiral nanocrystals.La chiralité est une propriété fascinante qui se manifeste à toutes les échelles de taille dans l'univers. À l'échelle nanométrique, les interactions entre la lumière polarisée circulairement et la matière chirale peuvent donner lieu à une activité chiroptique. Combinées aux propriétés optiques uniques des nanocristaux semi-conducteurs ultraminces, ces interactions constituent un riche terrain de jeu pour la création de nouveaux matériaux chiraux. Cependant, de nombreuses questionsfondamentales subsistent quant aux facteurs influençant la chiralité au sein des matériaux inorganiques à l'échelle nanométrique. Cette thèse vise à comprendre comment la chiralité peut être induite dans des systèmes ultraminces. Ceci est réalisé par le couplage électronique ligand-nanocristal et par la déformation de feuilles ultrafines en formes chirales. Le premier chapitre présente une introduction aux concepts scientifiques pertinents tirés de la littérature. Le deuxième chapitre démontre l’obtention de grandes amplitudes de dichroïsme circulaire et de luminescence polarisée circulairement dans des nanoplaquettes de perovskite de bromure de méthylammonium de plomb grâce à la chiralité induite par les ligands de surface. Les échantillons sont préparés en utilisant un mélange précis de ligands chiraux et non chiraux pour optimiser les signaux chiroptiques. La liaison compétitive des ligands est décrite à l'aide d'un modèle d'équilibre, élucidant les relations entre les ligands de surface et les propriétés chiroptiques. Le troisième chapitre étudie la chiralité structurelle qui peut être obtenue en contrôlant la conformation des nanoplaquettes hélicoïdales de CdSe par des contraintes de ligands de surface dépendant de la température. En modifiant le groupe fonctionnel du ligand et la chaîne alkyle, le rayon de courbure est modifié à la fois dans son ampleur et dans son signe, ce qui entraîne un changement de forme des nanoplaquettes. Ces changements sont attribués à de multiples facteurs, notamment la configuration de liaison du ligand, la désorption et la décomposition du ligand et la reconstruction de la surface du nanocristal. Enfin, le quatrième chapitre présente la recherche de nouveaux systèmes à changement de forme ultraminces basée sur la compréhension de l'interaction entre la chimie de surface, la structure cristalline et la conformation. Tout d'abord, il est démontré que l'échange de ligands par des acides alkylphosphoniques permet d’obtenir des domaines de ligands et permet d'aplatir les nanohélices de CdSe. D’autres systèmes sont explorés : les nanoplaquettes de sulfure de plomb et d'oxydes de lanthanides sont synthétisées, la transformation de phase des nano-monocouches de disulfure de tungstène est caractérisée et, enfin, l'enroulement de nano-serpentins de sulfure d'indium est démontré. Ces résultats font progresser la compréhension de la mécanique à l'échelle nanométrique, en aidant à élucider la relation entre la déformation des nanoplaquettes et la contrainte exercée par le ligand en surface. En découvrant les mécanismes qui sous-tendent la chiralité induite par le ligand et la déformation des nanoplaquettes, ces travaux ouvrent la voie à la conception rationnelle de nanocristaux chiraux ultraminces

Nanoplaquettes à changement de forme : induction de la chiralité dans les matériaux ultraminces

Chirality is a fascinating property manifesting on all size scales in the universe. At the nanoscale, interactions between circularly polarized light and chiral matter can result in chiroptical activity. Combined with the unique optical properties of ultrathin semiconducting nanocrystals, this creates a rich playground for the creation of novel chiral materials. However, many fundamental questions remain regarding the factors influencing chirality in inorganic nanoscale materials. This thesis aims to understand how chirality can be induced in ultrathin systems. This is achieved through electronic ligand-nanocrystal coupling, and by deforming ultrathin sheets into chiral shapes. The first chapter provides an introduction to relevant scientific concepts drawn from the literature. The second chapter demonstrates large magnitudes of circular dichroism and circularly polarized luminescence in methylammonium lead bromide perovskite nanoplatelets through ligand-induced chirality. Samples are prepared using a precise mixture of chiral and nonchiral ligands to optimize chiroptical signals.3The competitive ligand binding is described using an equilibrium model, elucidating relationships between the surface ligands and chiroptical properties. The third chapter demonstrates structural chirality by controlling the conformation of helical CdSe nanoplatelets through temperature-dependent surface ligand stresses. By altering the ligand functional group and alkyl chain, the radius of curvature is changed in both magnitude and sign, resulting in nanoplatelet ``shapeshifting''. These changes are attributed to multiple factors including ligand binding configuration, ligand desorption and decomposition, and nanocrystal surface reconstruction. The fourth chapter searches for new ultrathin shapeshifting systems by understanding the interplay between surface chemistry, crystal structure, and conformation. First, patch-wise phosphonic acid ligand exchange is shown to flatten CdSe nanohelices. Other systems are explored: lead sulfide and lanthanide oxide nanoplatelets are prepared, the phase transformation of tungsten disulfide nanomonolayers is characterized, and lastly, the unrolling of indium sulfide nanocoils is demonstrated. This work advances the understanding of mechanics at the nanoscale, helping to elucidate the relationship between nanoplatelet deformation and surface-ligand stress. By uncovering the mechanisms behind ligand-induced chirality and nanoplatelet curvature, this work paves the way towards the rational design of ultrathin chiral nanocrystals.La chiralité est une propriété fascinante qui se manifeste à toutes les échelles de taille dans l'univers. À l'échelle nanométrique, les interactions entre la lumière polarisée circulairement et la matière chirale peuvent donner lieu à une activité chiroptique. Combinées aux propriétés optiques uniques des nanocristaux semi-conducteurs ultraminces, ces interactions constituent un riche terrain de jeu pour la création de nouveaux matériaux chiraux. Cependant, de nombreuses questionsfondamentales subsistent quant aux facteurs influençant la chiralité au sein des matériaux inorganiques à l'échelle nanométrique. Cette thèse vise à comprendre comment la chiralité peut être induite dans des systèmes ultraminces. Ceci est réalisé par le couplage électronique ligand-nanocristal et par la déformation de feuilles ultrafines en formes chirales. Le premier chapitre présente une introduction aux concepts scientifiques pertinents tirés de la littérature. Le deuxième chapitre démontre l’obtention de grandes amplitudes de dichroïsme circulaire et de luminescence polarisée circulairement dans des nanoplaquettes de perovskite de bromure de méthylammonium de plomb grâce à la chiralité induite par les ligands de surface. Les échantillons sont préparés en utilisant un mélange précis de ligands chiraux et non chiraux pour optimiser les signaux chiroptiques. La liaison compétitive des ligands est décrite à l'aide d'un modèle d'équilibre, élucidant les relations entre les ligands de surface et les propriétés chiroptiques. Le troisième chapitre étudie la chiralité structurelle qui peut être obtenue en contrôlant la conformation des nanoplaquettes hélicoïdales de CdSe par des contraintes de ligands de surface dépendant de la température. En modifiant le groupe fonctionnel du ligand et la chaîne alkyle, le rayon de courbure est modifié à la fois dans son ampleur et dans son signe, ce qui entraîne un changement de forme des nanoplaquettes. Ces changements sont attribués à de multiples facteurs, notamment la configuration de liaison du ligand, la désorption et la décomposition du ligand et la reconstruction de la surface du nanocristal. Enfin, le quatrième chapitre présente la recherche de nouveaux systèmes à changement de forme ultraminces basée sur la compréhension de l'interaction entre la chimie de surface, la structure cristalline et la conformation. Tout d'abord, il est démontré que l'échange de ligands par des acides alkylphosphoniques permet d’obtenir des domaines de ligands et permet d'aplatir les nanohélices de CdSe. D’autres systèmes sont explorés : les nanoplaquettes de sulfure de plomb et d'oxydes de lanthanides sont synthétisées, la transformation de phase des nano-monocouches de disulfure de tungstène est caractérisée et, enfin, l'enroulement de nano-serpentins de sulfure d'indium est démontré. Ces résultats font progresser la compréhension de la mécanique à l'échelle nanométrique, en aidant à élucider la relation entre la déformation des nanoplaquettes et la contrainte exercée par le ligand en surface. En découvrant les mécanismes qui sous-tendent la chiralité induite par le ligand et la déformation des nanoplaquettes, ces travaux ouvrent la voie à la conception rationnelle de nanocristaux chiraux ultraminces

Monodisperse size-controlled 1T\u27-WS2 nano-monolayers with high colloidal stability

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\u27-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

Chiral Perovskite Nanoplatelets Exhibiting Circularly Polarized Luminescence through Ligand Optimization

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Chiral perovskite nanoplatelets exhibiting circularly polarized luminescence through ligand optimization

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

Critical role of water on the synthesis and gelling of gamma-In2S3 nanoribbons with giant aspect ratio

We report the synthesis of ultrathin indium sulfide In2S3 nanoribbons which display a giant aspect ratio using a simple and fast solvothermal method. They have a sub-nanometer thickness controlled at the atomic level, a width of (8.7 ± 0.1) nm and a length which can reach several micrometers. We determine the atomic composition of the inorganic core by Rutherford backscattering spectrometry (RBS) and measure by X-ray photoelectron spectrometry (XPS) an oleylamine surface coverage of 2.3 ligands per nm2. X-ray diffraction experiments and simulations as well as high-resolution dark-field STEM point toward a P3m1 trigonal crystallographic structure (g phase). Transport measurements show that the nanoribbons display n-type semiconductor unipolar behavior. Their lateral dimensions can be tuned by reaction time, temperature and by the amount of water present in the reaction medium: anhydrous synthesis conditions lead to hexagonal nanoplates, whereas controlled addition of water induces a symmetry break yielding long rectangular nanoribbons. Depending on the dispersion solvent, these long ribbon-like nanoparticles can form either well-dispersed colloids or bundles in which they stack face-to-face. Their large aspect ratio induces the formation of gels at volume fractions as low as 1.3 × 10-4 making them supergelators. The kinetics of gelation is strongly accelerated by an increase in the relative humidity of the ambient atmosphere

Critical role of water on the synthesis and gelling of gamma-In2S3 nanoribbons with giant aspect ratio

We report the synthesis of ultrathin indium sulfide In2S3 nanoribbons which display a giant aspect ratio using a simple and fast solvothermal method. They have a sub-nanometer thickness controlled at the atomic level, a width of (8.7 ± 0.1) nm and a length which can reach several micrometers. We determine the atomic composition of the inorganic core by Rutherford backscattering spectrometry (RBS) and measure by X-ray photoelectron spectrometry (XPS) an oleylamine surface coverage of 2.3 ligands per nm2. X-ray diffraction experiments and simulations as well as high-resolution dark-field STEM point toward a P3m1 trigonal crystallographic structure (g phase). Transport measurements show that the nanoribbons display n-type semiconductor unipolar behavior. Their lateral dimensions can be tuned by reaction time, temperature and by the amount of water present in the reaction medium: anhydrous synthesis conditions lead to hexagonal nanoplates, whereas controlled addition of water induces a symmetry break yielding long rectangular nanoribbons. Depending on the dispersion solvent, these long ribbon-like nanoparticles can form either well-dispersed colloids or bundles in which they stack face-to-face. Their large aspect ratio induces the formation of gels at volume fractions as low as 1.3 × 10-4 making them supergelators. The kinetics of gelation is strongly accelerated by an increase in the relative humidity of the ambient atmosphere

Insights into mammalian TE diversity through the curation of 248 genome assemblies.

We examined transposable element (TE) content of 248 placental mammal genome assemblies, the largest de novo TE curation effort in eukaryotes to date. We found that although mammals resemble one another in total TE content and diversity, they show substantial differences with regard to recent TE accumulation. This includes multiple recent expansion and quiescence events across the mammalian tree. Young TEs, particularly long interspersed elements, drive increases in genome size, whereas DNA transposons are associated with smaller genomes. Mammals tend to accumulate only a few types of TEs at any given time, with one TE type dominating. We also found association between dietary habit and the presence of DNA transposon invasions. These detailed annotations will serve as a benchmark for future comparative TE analyses among placental mammals