31 July 2021

[Nanotechnology] – Programmable plasmons by strain engineering.

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Nanotechnologies Codex International

Metal nanoparticles can concentrate light near their surface through the excitation of surface plasmons, which are collective oscillations of electrons. Depending on the size and shape of the metal particles, surface plasmons can show a range of different optical responses and colors.

These phenomena are useful for plasmon-enhanced applications ranging from ultrasensitive molecular sensing to fluorescence enhancement, where high-quality (i.e., narrow) and wavelength-tunable plasmonic resonances are particularly desirable.

Although narrow optical resonances and tailoring of the plasmonic resonance have been achieved independently, they have not yet been demonstrated within a single system.

The main challenge lies with the fact that either the optical responses are fixed at the time of fabrication or that intrinsic losses of the nanostructures cannot be suppressed to achieve narrow resonance linewidths.

“We have found a way to both realize narrow resonances and tune the resonance across the visible in aluminum nanoparticle arrays embedded in a PDMS slab,” Teri W. Odom, Charles E. and Emma H. Morrison Professor of Chemistry and Professor of Materials Science and Engineering at Northwestern University. “We discovered a new type of quadrupolar lattice mode with much narrower linewidth than the classic dipolar lattice mode.”

She points out that both modes can be programmed and reversibly engineered by simple mechanical stretching of the substrate. Since each mode can be independently optimized depending on the stretching direction, their single system can cover a large wavelength bandwidth and meet specific application requirements at the same time.

Odom and her team have reported their findings in PNAS.

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