Tunable Room-Temperature Synthesis of Coinage Metal Chalcogenide Nanocrystals from <i>N</i>‑Heterocyclic Carbene Synthons

We present a new toolset of precursors for semiconductor nanocrystal synthesis, N-heterocyclic carbene (NHC)-metal halide complexes, which enables a tunable molecular platform for the preparation of coinage metal chalcogenide quantum dots (QDs). Phase-pure and highly monodisperse coinage metal chalcogenide (Ag2E, Cu2–xE; E = S, Se) QDs are readily synthesized from the direct reaction of an NHC-MBr synthon (where M = Ag, Cu) with alkylsilyl chalcogenide reagents at room temperature. We demonstrate that the size of the resulting QDs is well-tailored by the electron-donating ability of the L-type NHC ligands, which are further confirmed to be the only organic capping ligands on the QD surface, imparting excellent colloidal stability. Local superstructures of the NHC-capped Ag2S QDs are observed by TEM, further demonstrating their potential for synthesizing monodisperse ensembles and mediating self-assembly

Compositionally Dependent Phase Identity of Colloidal CsPbBr_3–<i>x</i>I_<i>x</i> Quantum Dots

Compositionally Dependent Phase Identity of Colloidal CsPbBr3–xIx Quantum Dot

Correction to Tunable Room-Temperature Synthesis of Coinage Metal Chalcogenide Nanocrystals from <i>N</i>‑Heterocyclic Carbene Synthons

Correction to Tunable Room-Temperature Synthesis of Coinage Metal Chalcogenide Nanocrystals from <i>N</i>‑Heterocyclic Carbene Synthon

Local Structure of Ba_1–<i>x</i>Sr_<i>x</i>TiO₃ and BaTi_1–<i>y</i>Zr_<i>y</i>O₃ Nanocrystals Probed by X‑ray Absorption and X‑ray Total Scattering

The effect of isovalent chemical substitution on the magnitude and coherence length of local ferroelectric distortions present in sub-20 nm Ba1–xSrxTiO3 (x = 0.0, 0.30, 0.50, 1.0) and BaTi1–yZryO3 (y = 0.0, 0.15, 0.50, 1.0) nanocrystals synthesized at room temperature is investigated using X-ray absorption near edge structure (XANES) and pair distribution function analysis of X-ray total scattering data (PDF). Although the average crystal structure of the nanocrystals is adequately described by a centrosymmetric, cubic Pm3̅m space group, local ferroelectric distortions due to the displacement of the titanium atom from the center of the perovskite lattice are observed for all compositions, except BaZrO3. The symmetry of the ferroelectric distortions is adequately described by a tetragonal P4mm space group. The magnitude of the local displacements of the titanium atom in BaTiO3 nanocrystals is comparable to that observed in single crystals and bulk ceramics, but the coherence length of their ferroelectric coupling is much shorter (≤20 Å). Substitution of Sr2+ for Ba2+ and of Zr4+ for Ti4+ induces a tetragonal-to-cubic transition of the room temperature local crystal structure, analogous to that observed for single crystals and bulk ceramics at similar compositions. This transition is driven by a reduction of the magnitude of the local displacements of the titanium atom and/or of the coherence length of their ferroelectric coupling. Replacing 50% of Ba2+ with Sr2+ slightly reduces the magnitude of the titanium displacement, but the coherence length is not affected. In contrast, replacing 15% of the ferroelectrically active Ti4+ with Zr4+ leads to a significant reduction of the coherence length. Deviations from the ideal solid solution behavior are observed in BaTi1–yZryO3 nanocrystals and are attributed to an inhomogeneous distribution of the barium atoms in the nanocrystal. Composition–structure relationships derived for Ba1–xSrxTiO3 and BaTi1–yZryO3 nanocrystals demonstrate that the evolution of the room temperature local crystal structure with chemical composition parallels that of single crystals and bulk ceramics, and that chemical control over ferroelectric distortions is possible in the sub-20 nm size range. In addition, the potential of PDF analysis of total scattering data to probe compositional fluctuations in nanocrystals is demonstrated

Solution-Phase Synthesis of Well-Defined Indium Sulfide Nanorods

Solution-Phase Synthesis of Well-Defined Indium Sulfide Nanorod

Photochemical Synthesis of Bismuth Selenide Nanocrystals in an Aqueous Micellar Solution

The photolytic decomposition of triphenylbismuth and di-tert-butyl diselenide under aqueous micellar conditions yields 5-nm bismuth selenide nanocrystals of the BiSe stoichiometry. This is the first example of the bismuth-rich BiSe phase being prepared in a well-dispersed colloidal nanocrystal form

Synthesis of Metastable Wurtzite CuInSe₂ Nanocrystals

Synthesis of Metastable Wurtzite CuInSe2 Nanocrystal

Alkahest for V₂VI₃ Chalcogenides: Dissolution of Nine Bulk Semiconductors in a Diamine-Dithiol Solvent Mixture

The ability to solution deposit semiconductor films has received a great deal of recent attention as a way to potentially lower costs for many optoelectronic applications; however, most bulk semiconductors are insoluble in common solvents. Here we describe a novel and relatively nonhazardous binary solvent mixture comprised of 1,2-ethanedithiol and 1,2-ethylenediamine that possesses the remarkable ability to rapidly dissolve a series of nine bulk V2VI3 chalcogenides (V = As, Sb, Bi; VI = S, Se, Te) at room temperature and atmospheric pressure. After solution deposition and low-temperature annealing, the chalcogenides can be fully recovered as good quality, highly crystalline thin films with negligible organic content, as demonstrated for Sb2Se3 and Bi2S3

Tailoring the Mechanism of the Amorphous-to-Crystalline Phase Transition of PbTiO₃ via Kinetically Controlled Hydrolysis

A systematic investigation of the effects of hydrolytic conditions on the development of PbTiO3 (PTO) from amorphous metal–organic matrices is reported. Metal–organic matrices were obtained using a novel hydrolytic approach which relies on the kinetically controlled delivery of water vapor at the gas–liquid interface of a Pb–Ti alkoxide precursor. Crystallization was induced via standard thermal treatment and followed using X-ray diffraction, visible Raman spectroscopy, and thermal analysis. It was found that the mechanism of the amorphous-to-crystalline phase transition is controlled by the rate and extent of hydrolysis and polycondensation of the Pb–Ti alkoxide: faster and extended hydrolysis favors an amorphous-to-pyrochlore-to-perovskite transition, whereas slower and less extended hydrolysis favors a direct amorphous-to-perovskite transition. The rate and extent of hydrolysis were found to have a significant impact on the magnitude of the tetragonal distortion of the perovskite unit cell as well. Optimization of hydrolytic conditions allowed for well-crystallized, phase pure, tetragonal PTO to be obtained at temperatures as low as 500 °C via a direct amorphous-to-perovskite phase transition. Differences observed in the mechanism of perovskite phase formation are explained in terms of the differential dependence of the dynamics of lead and titanium atoms on hydrolytic conditions, the former being significantly more affected than the latter. Because long-range redistribution of lead atoms is the rate-determining step of the perovskite phase formation, this finding has implications for the design of metal–organic precursors and hydrolytic approaches targeting the preparation of lead-containing functional perovskite oxides