Browsing by Author "DeSantis, Christopher J."

Now showing 1 - 4 of 4
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    Ligand-Dependent Colloidal Stability Controls the Growth of Aluminum Nanocrystals
    (American Chemical Society, 2019) Clark, Benjamin D.; DeSantis, Christopher J.; Wu, Gang; Renard, David; McClain, Michael J.; Bursi, Luca; Tsai, Ah-Lim; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    The precise size- and shape-controlled synthesis of monodisperse Al nanocrystals remains an open challenge, limiting their utility for numerous applications that would take advantage of their size and shape-dependent optical properties. Here we pursue a molecular-level understanding of the formation of Al nanocrystals by titanium(IV) isopropoxide-catalyzed decomposition of AlH3ﾠin Lewis base solvents. As determined by electron paramagnetic resonance spectroscopy of intermediates, the reaction begins with the formation of Ti3+-AlH3ﾠcomplexes. Proton nuclear magnetic resonance spectroscopy indicates isopropoxy ligands are removed from Ti by Al, producing aluminum(III) isopropoxide and low-valent Ti3+ﾠcatalysts. These Ti3+ﾠspecies catalyze elimination of H2ﾠfrom AlH3ﾠinducing the polymerization of AlH3ﾠinto colloidally unstable low-valent aluminum hydride clusters. These clusters coalesce and grow while expelling H2ﾠto form colloidally stable Al nanocrystals. The colloidal stability of the Al nanocrystals and their size is determined by the molecular structure and density of coordinating atoms in the reaction, which is controlled by choice of solvent composition.
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    Plasmon and compositional mapping of plasmonic nanostructures
    (SPIE, 2014) Ringe, Emilie; Collins, Sean M.; DeSantis, Christopher J.; Skrabalak, Sara E.; Midgley, Paul A.
    Recently, co-reduction of Au and Pd has allowed the synthesis of complex Au core/AuPd shell nanoparticles with elongated tips and cubic-like symmetry. Optical studies have shown strong plasmonic behavior and high refractive index sensitivities. In this paper, we describe the composition and the near-field plasmonic behavior of those complex structures. Monochromated STEM-EELS, Cathodoluminescence, and EDS mapping reveals the different resonant modes in these particles, and shows that Pd, a poor plasmonic metal, does not prevent strong resonances and could actually be extremely helpful for plasmon-enhanced catalysis.
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    Polydopamine-Stabilized Aluminum Nanocrystals: Aqueous Stability and Benzo[a]pyrene Detection
    (American Chemical Society, 2019) Renard, David; Tian, Shu; Ahmadivand, Arash; DeSantis, Christopher J.; Clark, Benjamin D.; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    Aluminum nanocrystals have emerged as an earth-abundant material for plasmonics applications. Al nanocrystals readily oxidize in aqueous-based solutions, however, transforming into highly stratified γ-AlOOH nanoparticles with a 700% increase in surface area in a matter of minutes. Here we show that by functionalizing Al nanocrystals with the bioinspired polymer polydopamine, their stability in aqueous media is dramatically increased, maintaining their integrity in aqueous solution for over 2 weeks with no discernible structural changes. Polydopamine functionalization also provides a molecular capture layer that enables the capture of polycyclic aromatic hydrocarbon pollutants in H2O samples and their detection by surface-enhanced Raman spectroscopy, when polydopamine-stabilized Al nanocrystal aggregates are used as substrates. This approach was used to detect a prime carcinogenic H2O pollutant, benzo[a]pyrene with a sensitivity in the sub part-per-billion range.
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    Resonances of nanoparticles with poor plasmonic metal tips
    (Macmillan Publishers Limited, 2015) Ringe, Emilie; DeSantis, Christopher J.; Collins, Sean M.; Duchamp, Martial; Dunin-Borkowski, Rafal E.; Skrabalak, Sara E.; Midgley, Paul A.
    The catalytic and optical properties of metal nanoparticles can be combined to create platforms for light-driven chemical energy storage and enhanced in-situ reaction monitoring. However, the heavily damped plasmon resonances of many catalytically active metals (e.g. Pt, Pd) prevent this dual functionality in pure nanostructures. The addition of catalytic metals at the surface of efficient plasmonic particles thus presents a unique opportunity if the resonances can be conserved after coating. Here, nanometer resolution electron-based techniques (electron energy loss, cathodoluminescence, and energy dispersive X-ray spectroscopy) are used to show that Au particles incorporating a catalytically active but heavily damped metal, Pd, sustain multiple size-dependent localized surface plasmon resonances (LSPRs) that are narrow and strongly localized at the Pd-rich tips. The resonances also couple with a dielectric substrate and other nanoparticles, establishing that the full range of plasmonic behavior is observed in these multifunctional nanostructures despite the presence of Pd.