MSE Seminar: Electron Energy-Loss Spectroscopy for Designing Plasmonic Nanostructures for Room Temperature Reactions

Abstract: In situ transmission electron microscopy is now routinely used to measure the effect of external stimuli, such as temperature, gas or liquid environment, mechanical stress, etc., on the structure, chemistry, morphology and functioning of nanostructured materials. We are using high energy electrons generated by the monochromated source in an environmental scanning-transmission electron microscope (ESTEM) to excite localized surface plasmon (LSP) resonances in plasmonic nanoparticles and show how the energy produced during the dephasing of LSP modes can be used to initiate chemical reactions at room temperature.

In recent years, LSP resonance energy, excited using a light source, has been used to replace the thermal energy to initiate reactions at low temperatures, even at room temperature. Most of the plasmonic materials, Au, Ag or Al, are not generally catalytically active, i.e. do not adsorb most of the gas molecules, but have been successfully combined with active catalysts such as Pt, Ni, Ru, etc., for harvesting their LSP resonance energies for low-temperature reactions. So far optical methods have been used to generate and measure the LSP resonance energies where the wavelength of the light is carefully chosen to excite pacific LSP mode. Also, the low spatial resolution achievable by optical methods does not provide sub-particle level distribution of coupling efficiency of different modes. On the other hand, high energy electrons not only excite all LSP modes simultaneously, but also provide high spatial resolution in the nanometer range to resolve their energy loss probability that indicates the efficiency of coupling the location-specific electron excitation of the LSP modes at certain resonance energies on the plasmonic nanoparticle. Therefore, we use ESTEM, combined with metallic nanoparticle boundary element method and density functional theory simulations, to characterize various LSP modes and their coupling efficiency distribution within the shape and size-controlled nanoparticles of Au and Al. We have successfully applied the technique for CO disproportionation reaction and CO₂ reduction by carbon (Boudouard and reverse Boudouard reactions) at room temperature using Au and Al nanoparticles, respectively. We demonstrate that the knowledge gained from low-loss and core-loss EELS measurements can be extended to design catalyst-plasmonic particle combination for selected chemical reactions.

Bio: Renu Sharma is a project leader in the Nanoscale Imaging Group. She received a B.S. and B.Ed. in physics and chemistry from Panjab University, India, and a master's degree and doctorate in solid state chemistry from the University of Stockholm, Sweden, where she had a Swedish Institute Fellowship. Renu joined the CNST at NIST in 2009, coming from Arizona State University, where she began as a faculty research associate in the Department of Chemistry and Biochemistry and the Center for Solid State Science, and most recently served as a senior research scientist in the LeRoy Eyring Center for Solid State Science and as an affiliated faculty member in the School of Materials and Department of Chemical Engineering. Renu has been a pioneer in the development of environmental scanning transmission electron microscopy, combining atomic-scale dynamic imaging with chemical analysis to probe gas-solid reactions. She has applied this powerful technique to characterize the atomic-scale mechanisms underlying the synthesis and reactivity of nanoparticles (including catalysts), nanotubes, nanowires, inorganic solids, ceramics, semiconductors and superconductor materials. Renu has received a Bronze Medal of Service from Department of Commerce for developing new measurement techniques, a Deutscher Akademischer Austauschdienst (DAAD) Faculty Research Fellowship and is a past president of the Arizona Imaging and Microanalysis Society, a fellow of Microscopy Society of America and has given over 90 invited presentations and published five book chapters and over 200 research articles. At the CNST, Renu has established advanced E(S)TEM measurement capabilities that combine Raman spectroscopy, cathodoluminescence with electron diffraction, electron spectroscopy, high-resolution imaging and plasmonics for nanoscience research and is contributing her research expertise to the operation of a TEM facility in the NanoFab.

Host: Will Bowman