| AVS 66th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology Division | Friday Sessions |
| Session NS+AS-FrM |
| Session: | Electron-Beam Promoted Nanoscience |
| Presenter: | Wei-Chang Yang, National Institute of Standards and Technology (NIST) |
| Authors: | W.-C.D. Yang, National Institute of Standards and Technology (NIST) C. Wang, National Institute of Standards and Technology (NIST) L.A. Fredin, National Institute of Standards and Technology (NIST) H.J. Lezec, National Institute of Standards and Technology (NIST) R. Sharma, National Institute of Standards and Technology (NIST) |
| Correspondent: | Click to Email |
Optically-excited localized surface plasmon (LSP) resonances have been used to induce chemical reactions, such as hydrogen dissociation and ethylene epoxidation. Energy harnessed by plasmonic nanostructures and transferred to adsorbed reactants is theorized to initiate these chemical processes by compensating for the heat required otherwise. As we know, there are three important steps for designing a plasmonic catalyst system: (1) adsorption of reactants; (2) adequate resonance energy to overcome the reaction barrier; and (3) desorption of products. However, they have not been resolved at a sub-nanoparticle scale using optical methods. Herein, we demonstrate that the sub-particle information, gained from electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL), can be used to measure these steps for selected reactions.
LSP resonances, excited by electrons, on shape-controlled Au nanoparticles, were exploited to drive CO disproportionation: 2CO(g) --> CO2(g) + C(s), at room temperature (commonly initiated by heat above 400 ˚C) in an environmental scanning transmission electron microscope equipped with a monochromated electron gun. Triangular Au nanoprisms were synthesized and loaded on TiO2 support in a cantilevered configuration. In situ core-loss EELS was used to detect CO adsorption on the Au surfaces, for the first time, revealing the preferential adsorption sites at selective edges but not on the entire surfaces. Low-loss EELS maps of the Au nanoprisms showed that the electron beam was most efficiently coupled with the LSP dipole mode, indicated by the maximum EELS intensity, when placed at the cantilevered corner, suggesting a strong electric field caused by this specific mode at the same corner. In situ EELS showed that energy shifts occurred to the LSP resonance in CO environment and disappeared after CO evacuation, indicating a change in electron density of the Au particle as CO was adsorbed and desorbed, respectively. Energy transferred to the adsorbed CO was identified based on the spectral difference between EELS and CL. Carbon deposits, resulting from room-temperature CO disproportionation mediated by the LSP resonance, were detected by core-loss EELS at the cantilevered corner edge after evacuating CO. This shows that the active sites on the nanoprisms are where the preferable CO adsorption sites and the locations of maximum field amplitude superimpose.
Our findings provide unprecedented information on an LSP-induced chemical reaction with nanometer precision, shedding light on the design principles for new plasmonic catalysts that enable low-temperature reactions.