Dark plasmons could lead to more efficient solar cells

Dark plasmons, in contrast to emissive or bright plasmons with short lifetimes and broad linewidths greater than 50 nm, are nonradiative modes that enable subwavelength guiding of optical energy with no radiative loss, and consequently slowed depletion of trapped energy.

Aug 1st, 2011

Dark plasmons, in contrast to emissive or bright plasmons with short lifetimes and broad linewidths greater than 50 nm, are nonradiative modes that enable subwavelength guiding of optical energy with no radiative loss, and consequently slowed depletion of trapped energy. Such attributes are important, for example, to engineer more efficient photovoltaic solar cells. Until now, these subradiant or dark plasmons could only be supported by complex, difficult-to-fabricate nanostructures. But researchers at Northwestern University (Evanston, IL) have discovered a new type of dark plasmon that is manifested as a lattice plasmon resonance with an extremely narrow (approximately 5 nm full width half maximum) linewidth. The dark plasmons are created through out-of-plane dipolar coupling between large gold nanoparticles in a two-dimensional array. The subradiant modes can be statically tuned by changing the nanoparticle height or dynamically tuned by changing the incident illumination’s excitation angle.

The researchers fabricated gold nanoparticle arrays with varying heights of 65, 100, 120, and 170 nm in a polyurethane matrix on a glass substrate. Transverse-magnetic-polarized light directed to the array at an incident angle of 15º caused two types of resonance: a broad resonance peak centered around 730 nm, and a narrow resonance that shifted from 718 to 857 nm as the nanoparticle height increased from 65 to 170 nm. The experiment shows that dark out-of-plane plasmon modes in large-nanoparticle arrays can achieve nano-localized optical field enhancement with continuous spectral tunability over large areas on a variety of substrates.

Contact Teri Odom attodom@northwestern.edu.

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