Browsing by Author "Bursi, Luca"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item 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 NanophotonicsThe 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.Item Polarized evanescent waves reveal trochoidal dichroism(National Academy of Sciences, 2020) McCarthy, Lauren A.; Smith, Kyle W.; Lan, Xiang; Jebeli, Seyyed Ali Hosseini; Bursi, Luca; Alabastri, Alessandro; Chang, Wei-Shun; Nordlander, Peter; Link, Stephan; Laboratory for Nanoscale Spectroscopic Imaging at Rice; Laboratory for NanophotonicsMatter’s sensitivity to light polarization is characterized by linear and circular polarization effects, corresponding to the system’s anisotropy and handedness, respectively. Recent investigations into the near-field properties of evanescent waves have revealed polarization states with out-of-phase transverse and longitudinal oscillations, resulting in trochoidal, or cartwheeling, field motion. Here, we demonstrate matter’s inherent sensitivity to the direction of the trochoidal field and name this property trochoidal dichroism. We observe trochoidal dichroism in the differential excitation of bonding and antibonding plasmon modes for a system composed of two coupled dipole scatterers. Trochoidal dichroism constitutes the observation of a geometric basis for polarization sensitivity that fundamentally differs from linear and circular dichroism. It could also be used to characterize molecular systems, such as certain light-harvesting antennas, with cartwheeling charge motion upon excitation.