Creating ground truth for nanocrystal morphology: a fully automated pipeline for unbiased transmission electron microscopy analysis.

Control over colloidal nanocrystal morphology (size, size distribution, and shape) is important for tailoring the functionality of individual nanocrystals and their ensemble behavior. Despite this, traditional methods to quantify nanocrystal morphology are laborious. New developments in automated morphology classification will accelerate these analyses but the assessment of machine learning models is limited by human accuracy for ground truth, causing even unsupervised machine learning models to have inherent bias.

Probing the Ligand Exchange of N-Heterocyclic Carbene-Capped AgS Nanocrystals with Amines and Carboxylic Acids.

N-Heterocyclic carbenes (NHCs) are versatile L-type ligands that have been shown to stabilize coinage metal chalcogenide nanocrystals, such as AgS, remarkably well. However, very little research has been done on the interaction between NHC ligands and coinage metal chalcogenide nanocrystal surfaces and subsequent ligand exchange reactions. Herein, solution H nuclear magnetic resonance methods were used to monitor ligand exchange reactions on stoichiometric AgS nanocrystal platforms with various primary amine and carboxylic acid ligands.

The Surface Chemistry and Structure of Colloidal Lead Halide Perovskite Nanocrystals.

ConspectusSince the initial discovery of colloidal lead halide perovskite nanocrystals, there has been significant interest placed on these semiconductors because of their remarkable optoelectronic properties, including very high photoluminescence quantum yields, narrow size- and composition-tunable emission over a wide color gamut, defect tolerance, and suppressed blinking. These material attributes have made them attractive components for next-generation solar cells, light emitting diodes, low-threshold lasers, single photon emitters, and X-ray scintillators. While a great deal of research has gone into the various applications of colloidal lead halide perovskite nanocrystals, comparatively little work has focused on the fundamental surface chemistry of these materials.

Surface Termination of CsPbBr Perovskite Quantum Dots Determined by Solid-State NMR Spectroscopy.

Cesium lead halide perovskite quantum dots (QDs) have gained significant attention as next-generation optoelectronic materials; however, their properties are highly dependent on their surface chemistry. The surfaces of cuboidal CsPbBr QDs have been intensively studied by both theoretical and experimental techniques, but fundamental questions still remain about the atomic termination of the QDs. The binding sites and modes of ligands at the surface remain unproven.

Surface coordination chemistry of germanium nanocrystals synthesized by microwave-assisted reduction in oleylamine.

As surface ligands play a critical role in the colloidal stability and optoelectronic properties of semiconductor nanocrystals, we used solution NMR experiments to investigate the surface coordination chemistry of Ge nanocrystals synthesized by a microwave-assisted reduction of GeI in oleylamine. The as-synthesized Ge nanocrystals are coordinated to a fraction of strongly bound oleylamide ligands (with covalent X-type Ge-NHR bonds) and a fraction of more weakly bound (or physisorbed) oleylamine, which readily exchanges with free oleylamine in solution. The fraction of strongly bound oleylamide ligands increases with increasing synthesis temperature, which also correlates with better colloidal stability.

Phase control in the colloidal synthesis of well-defined nickel sulfide nanocrystals.

Morphologically well-defined colloidal nanocrystals of Ni3S4, NiS, Ni9S8, and Ni3S2 were independently prepared through a solution-phase synthesis using N,N'-disubstituted thioureas as the sulfur precursor. Synthetic control over phase and composition of the resulting colloidal nickel sulfide nanocrystals was achieved by primarily adjusting the reactivity of substituted thioureas as well as tuning the key reaction parameters of temperature and precursor ratio. In general, the more reactive N,N'-diphenyl thiourea yields more sulfur-rich phases (Ni3S4 and NiS) while less reactive N,N'-dibutyl thiourea yields sulfur-poor phases (Ni9S8 and Ni3S2).

Quantifying the Thermodynamics of Ligand Binding to CsPbBr Quantum Dots.

Cesium lead halide perovskites are an emerging class of quantum dots (QDs) that have shown promise in a variety of applications; however, their properties are highly dependent on their surface chemistry. To this point, the thermodynamics of ligand binding remain unstudied. Herein, H NMR methods were used to quantify the thermodynamics of ligand exchange on CsPbBr QDs.

Mono- and Mixed-Valence Tetrathiafulvalene Semiconductors (TTF)BiI and (TTF)BiI with 1D and 0D Bismuth-Iodide Networks.

Two new compounds containing tetrathiafulvalene (TTF) cations with extended and discrete anions based on Bi and I are reported. The compound (TTF)BiI comprises [BiII] chains of edge-shared octahedra that are interspersed with stacks of TTF. The compound (TTF)BiI has mixed-valence stacks of TTF and TTF and discrete molecules of TTF separated by discrete [BiI] anions.