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, 4 (13), 2147-2152

Tailoring Plasmon Coupling in Self-Assembled One-Dimensional Au Nanoparticle Chains Through Simultaneous Control of Size and Gap Separation

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Tailoring Plasmon Coupling in Self-Assembled One-Dimensional Au Nanoparticle Chains Through Simultaneous Control of Size and Gap Separation

Tianhong Chen et al. J Phys Chem Lett.

Abstract

We investigated the near- and far-field response of one-dimensional chains of Au nanoparticles (NPs) fabricated with high structural control through template guided self-assembly. We demonstrate that the density of polyethylene glycol (PEG) ligands grafted onto the NP surface, in combination with the buffer conditions, facilitate a systematic variation of the average gap width (g) at short separations of g<1.1nm. The overall size (n) of the cluster was controlled through the template. The ability to independently vary n and g allowed for a rational tuning of the spectral response in individual NP clusters over a broad spectral range. We used this structural control for a systematic investigation of the electromagnetic coupling underlying the superradiant cluster mode. Independent of the chain length, plasmon coupling is dominated by direct neighbor interactions. A decrease in coupling strength at separations ≲0.5nm indicates the presence of non-local and/or quantum mechanical coupling mechanisms.

Keywords: Metamaterials; Nanofabrication; Plasmonic Molecules; Quantum Plasmonics; Self-Assembly.

Figures

Figure 1
Figure 1
GMT simulated normalized spectral shift S (a) and peak near-field intensity enhancement (|E|2/|E0|2) (b) as function of cluster size (n) and interparticle separation (g). (c) Near-field intensity enhancement maps calculated at the wavelength of peak enhancement for n = 4 (top) and n = 5 (bottom). Insets show enlargements of the hottest-spots in the two clusters with rescaled (|E|2/|E0|2) color map.
Figure 2
Figure 2
(a) Schematic flow chart of the template guided self-assemble approach used for fabricating 1D NP clusters; (b) Scattering spectra and corresponding SEM images of 1D clusters of various sizes; monomer (black) and dimer (red) spectra are smoothed by a 9 point sliding average.
Figure 3
Figure 3
(a) Experimental normalized spectral shift S as function of cluster size (n) and interparticle separation (g). (b) Natural log of the peak shift ratio versus the inverse of cluster size (1/n).
Figure 4
Figure 4
(a) HRTEM pictures of 1D clusters formed from NPNC in T40 buffer, scale bar represents 50nm. (b) Cumulative probability plots for the interparticle gap distributions obtained under three different experimental conditions as defined in the legend.

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