More Like this

1. Inductively Coupled Nonthermal Plasma Synthesis of Size-Controlled γ-Al2O3 Nanocrystals

   https://doi.org/10.3390/nano13101627  

   Xiong, Zichang; Andaraarachchi, Himashi P.; Held, Jacob T.; Dorn, Rick W.; Jeong, Yong-Jin; Rossini, Aaron; Kortshagen, Uwe R. (May 2023, Nanomaterials)

   Gamma alumina (γ-Al2O3) is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. However, synthesis of γ-Al2O3 nanocrystals is often a complicated process requiring high temperatures or additional post-synthetic steps. Here, we report a single-step synthesis of size-controlled and monodisperse, facetted γ-Al2O3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Under optimized conditions, we observed phase-pure, cuboctahedral γ-Al2O3 nanocrystals with defined surface facets. Nuclear magnetic resonance studies revealed that nanocrystal surfaces are populated with AlO6, AlO5 and AlO4 units with clusters of hydroxyl groups. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small as 3.5 nm, below the predicted thermodynamic stability limit for γ-Al2O3. 

   more » « less
2. Monolayer Support Control and Precise Colloidal Nanocrystals Demonstrate Metal–Support Interactions in Heterogeneous Catalysts

   https://doi.org/10.1002/adma.202104533  

   Goodman, Emmett_D; Asundi, Arun_S; Hoffman, Adam_S; Bustillo, Karen_C; Stebbins, Jonathan_F; Bare, Simon_R; Bent, Stacey_F; Cargnello, Matteo (September 2021, Advanced Materials)

   Abstract Electronic and geometric interactions between active and support phases are critical in determining the activity of heterogeneous catalysts, but metal–support interactions are challenging to study. Here, it is demonstrated how the combination of the monolayer‐controlled formation using atomic layer deposition (ALD) and colloidal nanocrystal synthesis methods leads to catalysts with sub‐nanometer precision of active and support phases, thus allowing for the study of the metal–support interactions in detail. The use of this approach in developing a fundamental understanding of support effects in Pd‐catalyzed methane combustion is demonstrated. Uniform Pd nanocrystals are deposited onto Al₂O₃/SiO₂spherical supports prepared with control over morphology and Al₂O₃layer thicknesses ranging from sub‐monolayer to a ≈4 nm thick uniform coating. Dramatic changes in catalytic activity depending on the coverage and structure of Al₂O₃situated at the Pd/Al₂O₃interface are observed, with even a single monolayer of alumina contributing an order of magnitude increase in reaction rate. By building the Pd/Al₂O₃interface up layer‐by‐layer and using uniform Pd nanocrystals, this work demonstrates the importance of controlled and tunable materials in determining metal–support interactions and catalyst activity. 

   more » « less
3. Synthesis of TlBr and Tl ₂ AgBr ₃ Nanocrystals

   https://doi.org/10.1002/cnma.202000100  

   Siegler, Timothy_D; Shah, Tushti; Houck, Daniel_W; Suri, Mokshin; Zhang, Yangning; Korgel, Brian_A (March 2020, ChemNanoMat)

   Abstract There are only a few examples of nanocrystal synthesis with thallium (Tl). Here, we report the synthesis of uniform, ligand‐stabilized colloidal nanocrystals of TlBr and Tl₂AgBr₃nanocrystals with average diameter ranging between 10 and 20 nm. TlBr nanocrystals are made by hot injection of trimethylsilyl bromide (TMSBr) into solutions of oleylamine, oleic acid and octadecene with thallium (III) or thallium (I) acetate. Tl₂AgBr₃nanocrystals form when silver (I) acetate is included in the reaction. The TlBr nanocrystals have CsCl crystal structure with a direct band gap of 3.1 eV. The Tl₂AgBr₃nanocrystals have trigonal dolomite crystal structure with an indirect band gap of 3.1 eV. The TlBr nanocrystals made with thallium (III) were sufficiently uniform to assemble into face‐centered cubic (fcc) superlattices. 

   more » « less
4. Understanding quantum confinement and ligand removal in solution-based ZnO thin films from highly stable nanocrystal ink

   https://doi.org/10.1039/C8TC01536H  

   Sun, Yuhang; Donaldson, Preston D.; Garcia-Barriocanal, Javier; Swisher, Sarah L. (January 2018, Journal of Materials Chemistry C)

   We report a synthesis procedure for dodecanethiol capped wurtzite ZnO nanocrystals with an average diameter of 4 nm that are monodisperse, highly soluble, and shelf-stable for many months. Compared to previous ZnO ink recipes, we demonstrate improved particle solubility and excellent ink stability, resulting in ZnO nanocrystal inks that are optimized for printed electronics applications. The ZnO nanocrystal solution exhibits an absorption peak at 341 nm (3.63 eV), which represents a blue-shift of approximately 0.3 eV from the bulk ZnO bandgap (∼3.3 eV). This blue shift is consistent with previously reported models for an increased bandgap due to quantum confinement. We used variable-angle spectroscopic ellipsometry (VASE) to determine the optical properties of solution-processed thin films of ZnO nanocrystals, which provides valuable insight into the changes in film composition and morphology that occur during thermal annealing treatments ranging from 150–300 °C. The ZnO nanocrystals maintain their quantum confinement when deposited into a thin film, and the degree of quantum confinement is gradually reduced as the thermal annealing temperature increases. Using infrared absorption measurements (FTIR) and X-ray photoelectron spectroscopy (XPS), we show that the dodecanethiol ligands are removed from the ZnO films during annealing, resulting in a high-purity semiconductor film with very low carbon contamination. Furthermore, we show that annealing at 300 °C results in complete ligand removal with only a slight increase in grain size. Thin-film transistors (TFT) using ZnO nanocrystals as the channel material annealed at 300 °C show moderate mobility (∼0.002 cm 2 V −1 s −1 ) and good on/off ratio >10 4 . These results demonstrate the distinct advantages of colloidal nanocrystals for printed electronics applications: the composition and morphology of the solution-processed film can be carefully tuned by controlling the size and surface coating of the nanocrystals in the ink. 

   more » « less
5. Nucleation, growth, and superlattice formation of nanocrystals observed in liquid cell transmission electron microscopy

   https://doi.org/10.1557/mrs.2020.229  

   Chen, Qian; Yuk, Jong Min; Hauwiller, Matthew R.; Park, Jungjae; Dae, Kyun Seong; Kim, Jae Sung; Alivisatos, A. Paul (September 2020, MRS Bulletin)

   null (Ed.)

   This article reviews the advancements and prospects of liquid cell transmission electron microscopy (TEM) imaging and analysis methods in understanding the nucleation, growth, etching, and assembly dynamics of nanocrystals. The bonding of atoms into nanoscale crystallites produces materials with nonadditive properties unique to their size and geometry. The recent application of in situ liquid cell TEM to nanocrystal development has initiated a paradigm shift, (1) from trial-and-error synthesis to a mechanistic understanding of the “synthetic reactions” responsible for the emergence of crystallites from a disordered soup of reactive species (e.g., ions, atoms, molecules) and shape-defined growth or etching; and (2) from post-processing characterization of the nanocrystals’ superlattice assemblies to in situ imaging and mapping of the fundamental interactions and energy landscape governing their collective phase behaviors. Imaging nanocrystal formation and assembly processes on the single-particle level in solution immediately impacts many existing fields, including materials science, nanochemistry, colloidal science, biology, environmental science, electrochemistry, mineralization, soft condensed-matter physics, and device fabrication. 

   more » « less