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  1. Abstract Remote epitaxy is a promising approach for synthesizing exfoliatable crystalline membranes and enabling epitaxy of materials with large lattice mismatch. However, the atomic scale mechanisms for remote epitaxy remain unclear. Here we experimentally demonstrate that GaSb films grow on graphene-terminated GaSb (001) via a seeded lateral epitaxy mechanism, in which pinhole defects in the graphene serve as selective nucleation sites, followed by lateral epitaxy and coalescence into a continuous film. Remote interactions are not necessary in order to explain the growth. Importantly, the small size of the pinholes permits exfoliation of continuous, free-standing GaSb membranes. Due to the chemicalmore »similarity between GaSb and other III-V materials, we anticipate this mechanism to apply more generally to other materials. By combining molecular beam epitaxy with in-situ electron diffraction and photoemission, plus ex-situ atomic force microscopy and Raman spectroscopy, we track the graphene defect generation and GaSb growth evolution a few monolayers at a time. Our results show that the controlled introduction of nanoscale openings in graphene provides an alternative route towards tuning the growth and properties of 3D epitaxial films and membranes on 2D material masks.« less
    Free, publicly-accessible full text available December 1, 2023
  2. Free, publicly-accessible full text available August 17, 2023
  3. Triarylmethanols are well-known core structures in natural products and pharmacologically relevant compounds. In general, transition metal-based catalysts or highly reactive organometallics are employed for the synthesis of these compounds. Herein, we report the regioselective tandem C(sp 3 )–H arylation/oxidation of diarylmethanes with nitroarenes to generate arylated alcohols. The present method is general, mild, green, and conducted in air at room temperature. Furthermore, use of triarylmethanes as pro-nucleophiles provides straightforward access to select tetraarylmethanes through a cross-dehydrogenative coupling process.
    Free, publicly-accessible full text available July 12, 2023
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  7. A photochemical C(sp 3 )–H oxygenation of alkane and arene substrates catalyzed by [NEt 4 ] 2 [Ce IV Cl 6 ] under mild conditions (1 atm, 25 °C) is described. Time-course studies reveal that the hydrocarbons are oxidized in a stepwise fashion to afford alcohols, aldehydes, ketones, and carboxylic acids. The catalyst resting state, [Ce IV Cl 6 ] 2− , is observed by UV-visible spectroscopy. On/off light-switching experiments, quantum yield measurements, and the absence of a kinetic isotope effect on parallel C–H/C–D functionalization suggest that ligand-to-metal charge transfer of [NEt 4 ] 2 [Ce IV Cl 6 ]more »to generate Cl˙ is the turnover-limiting step. The involvement of a highly reducing excited-state [NEt 4 ] 3 [Ce III Cl 6 ]* species as well as photo-excited aldehyde, under black light irradiation appears to facilitate the conversion of primary alcohols and aldehydes to carboxylic acids. Remarkably, this approach is found to be capable of direct activation of light alkanes, including methane and ethane.« less
    Free, publicly-accessible full text available May 17, 2023
  8. Enantioenriched azaarylmethyl amine derivatives are useful building blocks in synthetic and medicinal chemistry. To access these valuable motifs, an enantioselective palladium-catalyzed benzylation of azaarylmethyl amine pronucleophiles is introduced. Of note, this is a rare application of asymmetric (2-naphthyl)methylation of pro-nucleophiles with high p K a values (p K a ≈ 34 in DMSO). Control experiments support the notion that the coordination of Li + to the azaaryl nitrogen plays a critical role in the substitution process. With this procedure, enantioenriched (2-naphthyl)methylene azaarylmethyl amines with a variety of azaaryl groups (pyridyl, pyrazine, quinoxaline and isoquinoline) and cyclic and acyclic amines aremore »readily obtained with good yields and enantioselectivities up to 99%.« less
    Free, publicly-accessible full text available May 17, 2023
  9. Stable glasses (SGs) are formed through surface-mediated equilibration (SME) during physical vapor deposition (PVD). Unlike intermolecular interactions, the role of intramolecular degrees of freedom in this process remains unexplored. Here, using experiments and coarse-grained molecular dynamics simulations, we demonstrate that varying dihedral rotation barriers of even a single bond, in otherwise isomeric molecules, can strongly influence the structure and stability of PVD glasses. These effects arise from variations in the degree of surface mobility, mobility gradients, and mobility anisotropy, at a given deposition temperature ( T dep ). At high T dep , flexible molecules have access to more configurations,more »which enhances the rate of SME, forming isotropic SGs. At low T dep , stability is achieved by out of equilibrium aging of the surface layer. Here, the poor packing of rigid molecules enhances the rate of surface-mediated aging, producing stable glasses with layered structures in a broad range of T dep . In contrast, the dynamics of flexible molecules couple more efficiently to the glass layers underneath, resulting in reduced mobility and weaker mobility gradients, producing unstable glasses. Independent of stability, the flattened shape of flexible molecules can also promote in-plane orientational order at low T dep . These results indicate that small changes in intramolecular relaxation barriers can be used as an approach to independently tune the structure and mobility profiles of the surface layer and, thus, the stability and structure of PVD glasses.« less
    Free, publicly-accessible full text available June 28, 2023
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