Research ArticleNANOMATERIALS

From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties

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Science Advances  04 Dec 2015:
Vol. 1, no. 11, e1500988
DOI: 10.1126/sciadv.1500988
  • Fig. 1 Reversible redox tuning of Au/Ag nanoparticles.

    (A) Nanoparticle shells were reversibly switched between Ag and AgCl using redox electrochemistry. The optical response to redox tuning was measured using single-particle spectroscopy under electrochemical potential control. (B) HAADF-STEM and EDS elemental maps of a single Au/Ag nanoparticle show clear core-shell geometry. (C) Mean response over five cycles of changes in resonance energy (ΔE), full width at half maximum (ΔΓ), and intensity (ΔI) as a function of applied potential under different electrolyte conditions. (Inset) Small-intensity response for control and thin-shell cases. Shaded bounds indicate standard error. au, arbitrary units.

  • Fig. 2 Dimer surface plasmon response to reversible electrochemical redox tuning.

    (A) Thin shells on strongly coupled Au dimers were reversibly switched between Ag and AgCl. Charge density maps of the core and shell surfaces show that the optical response is dominated by Au cores in Au/AgCl dimers, but by Ag shells in Au/Ag dimers. Maps were generated at 1.88 eV. (B) Scattering spectra during dynamic potential control show clear modulation with changes in shell composition. (C) Mean LB mode ΔE, ΔΓ, and ΔI over five cycles as a function of applied potential. Shaded bounds indicate standard error (smaller than linewidth at most points).

  • Fig. 3 Reversible electrochemical tuning of a dimer between capacitive and conductive coupling.

    (A) Overlapping shells on Au dimers were switched between Ag and AgCl to create a switch between capacitive and conductive coupling. TEM image shows an Au dimer enveloped by Ag shell. (B) Simulated and experimental scattering spectra show a drastic optical response to switching the plasmon coupling mechanism. (C) Series of scattering spectra during step potential application to switch shell composition. (D) Surface charge density plots of shell and core surfaces for SB and LB modes. Charge plots were calculated at 2.0 eV for the SB mode and at 1.67 eV for the LB mode.

  • Fig. 4 Dynamic evolution of the CTP mode using 40-nm Au cores and decreased overpotential.

    (A) Experimental static (top) and dynamic (bottom) scattering observations of slow bridging during the conversion between AgCl and Ag shells for an individual Au/Ag dimer with 40-nm Au cores at −0.22 V. (Inset) Surface charge density plot of the outer Ag shell surface for the CTP mode (calculated at 1.35 eV). (B) Predicted spectral evolution with electrochemical shell conversion from pure AgCl to pure Ag using isotropic dielectric mixing approximation. (C) CTP mode splitting in simulations using bridged concentric Ag growth mechanism at the point of Ag shell overlap (full evolution in fig. S10B).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/11/e1500988/DC1

    Fig. S1. EDS spectrum and line scan profile of single Au/Ag nanoparticle.

    Fig. S2. Surface charge plots for an Au/Ag core-shell nanoparticle.

    Fig. S3. Transmission electron micrographs showing the native structure of gold nanoparticle dimers and size analysis of single gold nanoparticles.

    Fig. S4. Surface charge plots for the T mode for thin-shelled dimers.

    Fig. S5. Effects of increasing shell thickness on Ag and AgCl shells.

    Fig. S6. Digital color images taken with an SLR (single-lens reflex) camera at microscope eyepiece during initial electrodeposition.

    Fig. S7. Color images of Au/Ag single particles and dimers under oxidizing and reducing conditions.

    Fig. S8. Charge density maps of T modes for both shell states for bridged dimers.

    Fig. S9. Effects of varying Au core size on Au/Ag bridged dimers.

    Fig. S10. Mode evolution with increasing Ag content under concentric spherical growth hypotheses.

    Fig. S11. Evolution of the SB mode with increasing Ag shell thickness.

    Fig. S12. Cyclic voltammogram with and without illumination of the working electrode.

    Fig. S13. Electrochemical characterization of the Au/Ag surface reaction.

    Fig. S14. Diagram showing sample geometry used in FEM simulations.

    Video S1. Effects of redox tuning for a conductively bridged dimer.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. EDS spectrum and line scan profile of single Au/Ag nanoparticle.
    • Fig. S2. Surface charge plots for an Au/Ag core-shell nanoparticle.
    • Fig. S3. Transmission electron micrographs showing the native structure of gold nanoparticle dimers and size analysis of single gold nanoparticles.
    • Fig. S4. Surface charge plots for the T mode for thin-shelled dimers.
    • Fig. S5. Effects of increasing shell thickness on Ag and AgCl shells.
    • Fig. S6. Digital color images taken with an SLR (single-lens reflex) camera at microscope eyepiece during initial electrodeposition.
    • Fig. S7. Color images of Au/Ag single particles and dimers under oxidizing and reducing conditions.
    • Fig. S8. Charge density maps of T modes for both shell states for bridged dimers.
    • Fig. S9. Effects of varying Au core size on Au/Ag bridged dimers.
    • Fig. S10. Mode evolution with increasing Ag content under concentric spherical growth hypotheses.
    • Fig. S11. Evolution of the SB mode with increasing Ag shell thickness.
    • Fig. S12. Cyclic voltammogram with and without illumination of the working electrode.
    • Fig. S13. Electrochemical characterization of the Au/Ag surface reaction.
    • Fig. S14. Diagram showing sample geometry used in FEM simulations.
    • Legend for video S1

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    Other Supplementary Material for this manuscript includes the following:

    • Video S1 (.mp4 format). Effects of redox tuning for a conductively bridged dimer.

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