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Femtosecond laser reshaping yields gold nanorods with ultranarrow surface plasmon resonances

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Science  03 Nov 2017:
Vol. 358, Issue 6363, pp. 640-644
DOI: 10.1126/science.aan8478

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Laser-shaping nanoparticles

For many applications of the plasmon resonances of metal nanoparticles, it is necessary to have narrow resonance lines. However, most methods for synthesizing nanoparticles create a distribution of sizes and shapes that broaden the resonance lines. González-Rubio et al. annealed gold nanorods dispersed in an aqueous solution of a surfactant with carefully tuned ultrafast (femtosecond) laser pulses. This approach reshaped the nanoparticles to create a near-uniform distribution with resonance lines nearly as sharp as for a single nanorod.

Science, this issue p. 640

Abstract

The irradiation of gold nanorod colloids with a femtosecond laser can be tuned to induce controlled nanorod reshaping, yielding colloids with exceptionally narrow localized surface plasmon resonance bands. The process relies on a regime characterized by a gentle multishot reduction of the aspect ratio, whereas the rod shape and volume are barely affected. Successful reshaping can only occur within a narrow window of the heat dissipation rate: Low cooling rates lead to drastic morphological changes, and fast cooling has nearly no effect. Hence, a delicate balance must be achieved between irradiation fluence and surface density of the surfactant on the nanorods. This perfection process is appealing because it provides a simple, fast, reproducible, and scalable route toward gold nanorods with an optical response of exceptional quality, near the theoretical limit.

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