Ahhyun Jeong

Addresses a need to gain scientific insights from one-dimensional (1D) scientific spectra in model-independent ways. A powerful approach for this is to take differences between pairs of spectra and look for meaningful changes that might indicate underlying chemical, structural, or other modifications. The challenge is that the difference curve may contain uninteresting differences such as experimental inconsistencies and benign physical changes such as the effects of thermal expansion. allows researchers to apply simple transformations, or “morphs,” to one of the datasets to remove the unwanted differences, revealing, when they are present, nontrivial differences. is an open-source Python package available on the Python Package Index and conda-forge. Here, we describe its functionality and apply it to solve a range of experimental challenges on diffraction and pair distribution function data from x-rays and neutrons, though we note that it may be applied to any 1D function in principle.

Nanocrystals (NCs) serve as versatile building blocks for the creation of functional materials with NC self-assembly offering opportunities to enable novel material properties. Here, we demonstrate that PbS NCs functionalized with strongly negatively charged metal chalcogenide complex (MCC) ligands, such as Sn₂S₆^4- and AsS₄^3-, can self-assemble into all-inorganic superlattices with both long-range superlattice translational and atomic-lattice orientational order. Structural characterizations reveal that the NCs adopt an unexpected edge-to-edge alignment, and numerical simulation clarifies that orientational order is thermodynamically stabilized by many-body ion correlations originating from the dense electrolyte. Furthermore, we show that the superlattices of Sn₂S₆^4--functionalized PbS NCs can be fully disassembled back into the colloidal state, which is highly unusual for orientationally attached superlattices with atomic-lattice alignment. The reversible oriented attachment of NCs, enabling their dynamic assembly and disassembly into effectively single-crystalline superstructures, offers a pathway toward designing reconfigurable materials with adaptive and controllable electronic and optoelectronic properties.

Colloidal quantum dots offer tunable optical properties for optoelectronic applications, but the synthesis of high-quality III–V quantum dots (QDs) other than indium pnictides, and particularly GaAs, has remained elusive due to synthetic challenges. Colloidal GaAs QDs have been reported very recently and have shown only weak band-edge photoluminescence. Here, we demonstrate a large-scale synthesis of colloidal GaAs QDs in molten salts, followed by a high-temperature surface treatment with K₂S, which removes native oxide and enables uniform zinc chalcogenide shell growth on GaAs. These QDs demonstrate bright band-edge photoluminescence and electroluminescence in QD LED devices. Low-temperature spectroscopy reveals a well-resolved exciton fine structure with distinct bright-state splitting and temperature-independent decay dynamics from 4 to 100 K. These results establish a practical pathway for the preparation of high-quality colloidal GaAs QDs from molten salts with potential applications in quantum technologies and optoelectronics.

The cluster regime of colloidal semiconductor quantum dots (QDs) occupies an interesting space on the continuum from molecule to bulk material and allows for the study of QD properties at extreme quantum confinement limits. For typical QDs, several size-dependent trends are well-established, including intraband relaxation rates and the universal scaling of Auger recombination with particle volume. Advances in synthesis now allow isolation of atomically precise semiconductor magic-size clusters (MCs), which offer experimental insight regarding how the electronic structure changes with the particle size in the ultrasmall limit. We report intraband cooling and Auger recombination for several stable CdSe MCs as a function of the particle size and observe deviation from the QD response in the cluster regime. We additionally present optical signatures ascribed to transient disordering that appear in the single-exciton regime for MCs, which point to complexities regarding the implementation of MCs in optoelectronic devices.

Gallium pnictides, such as GaAs and GaP, are among the most widely used semiconductors for electronic, optoelectronic, and photonic applications. However, solution syntheses of gallium pnictide nanomaterials are less developed than those of many other colloidal semiconductors, including indium pnictides, II-VI and IV-VI compounds, and lead halide perovskites. In this work, we demonstrate that the Wells dehalosilylation reaction can be carried out in molten inorganic salt solvents to synthesize colloidal GaAs, GaP, and GaP_1-xAs_x nanocrystals. We demonstrate that discrete colloidal nanocrystals can be nucleated and grown in a molten salt with control over their size and composition. Additionally, we found that reaction temperatures above 400 °C are crucial for annealing structural defects in GaAs nanocrystals. We also highlight the utility of the as-synthesized GaP nanocrystals by showing that GaP can be solution-processed into high-refractive-index coatings and patterned by direct optical lithography with micron resolution. Finally, we demonstrate that dehalosilylation reactions in molten salts can be generalized to synthesize indium pnictide (Pn = As, P) and ternary (In_1-xGa_xAs and In_1-xGa_xP) quantum dots.

Colloidal quantum dots, with their size-tunable optoelectronic properties and scalable synthesis, enable applications in which inexpensive high-performance semiconductors are needed. Synthesis science breakthroughs have been key to the realization of quantum dot technologies, but important group III–group V semiconductors, including colloidal gallium arsenide (GaAs), still cannot be synthesized with existing approaches. The high-temperature molten salt colloidal synthesis introduced in this work enables the preparation of previously intractable colloidal materials. We directly nucleated and grew colloidal quantum dots in molten inorganic salts by harnessing molten salt redox chemistry and using surfactant additives for nanocrystal shape control. Synthesis temperatures above 425°C are critical for realizing photoluminescent GaAs quantum dots, which emphasizes the importance of high temperatures enabled by molten salt solvents. We generalize the methodology and demonstrate nearly a dozen III-V solid-solution nanocrystal compositions that have not been previously reported.