Dr. Ward L. Johnson Profile

Dr. Ward L. Johnson

at National Institute of Standards and Technology

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Proceedings Article | 26 August 2008 Paper

Surface-plasmon fields in two-dimensional arrays of gold nanodisks

W. Johnson, S. Kim, Z. Utegulov, B. Draine

Proceedings Volume 7032, 70321S (2008) https://doi.org/10.1117/12.795608

KEYWORDS: Gold, Absorption, Light scattering, Interfaces, Surface plasmons, Refraction, Photovoltaics, Scattering, Phonons, Nanolithography

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Distributions of electric fields in two-dimensional arrays of gold nanodisks on Si₃N₄ membranes are modeled by use of the discrete-dipole approximation as a function of nanodisk diameter (20 nm to 50 nm), height (10 nm to 100 nm), ratio of the array spacing to diameter (1.3 to 4.7), and angle of incident light. The primary focus is on fields in a plane near the circular gold/vacuum interface with light of 532 nm wavelength incident through the membrane, a configuration that is particularly relevant to potential applications in plasmon-mediated Brillouin light scattering, nanolithography, and photovoltaics. The height/diameter ratio for maximum intensities over this plane is between 0.7 and 1.5 and not strongly dependent on the spacing for a given angle. The average intensity increases with decreasing array spacing and incident angle relative to the substrate normal. This dependence is attributed primarily to a combination of fractional coverage area of the gold and increased excitation of a dipolar contribution to the fields. The incident light at 532 nm simultaneously excites dipolar and quadrupolar surface-plasmon modes. Because the quadrupolar mode has a peak close to 532 nm, its excited fields are approximately out of phase with the incident light.

Proceedings Article | 22 September 2007 Paper

Surface-plasmon enhancement of Brillouin light scattering from gold-nanodisk arrays on glass

Z. Utegulov, J. Shaw, B. Draine, S. Kim, W. Johnson

Proceedings Volume 6641, 66411M (2007) https://doi.org/10.1117/12.735253

KEYWORDS: Gold, Glasses, Acoustics, Scattering, Light scattering, Surface plasmons, Interfaces, Rayleigh scattering, Silver, Standards development

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Enhancement of Brillouin light scattering (BLS) at the wavelength of 532 nm was observed from Rayleigh-like and Sezawa-like acoustic modes of alkaline-earth boro-aluminosilicate glass covered with periodic arrays of gold nanodisks. This enhancement is attributed to mediation of surface plasmons of the nanodisks. For nanodisks with diameters of 71 nm to 90 nm, heights of 30 nm, and periodicity of 100 nm, the maximum measured surface-plasmon enhancement of BLS intensity was, respectively, ~ 2.4 and ~ 5.6 for Rayleigh-like and Sezawa-like modes, relative to the intensity from a gold film with the same fractional coverage area but without surface-plasmon coupling. The maximum for the Rayleigh-like modes occurs with the smallest-diameter nanodisks, and that for the Sezawa-like modes occurs with the largest-diameter nanodisks. The angular dependence is relatively broad. Calculations employing the discrete dipole approximation were used to predict the electric-field intensities in the gold disks and nearby glass as a function of nanodisk diameter. The average calculated intensity at the top surface of the gold increases with decreasing diameter, consistent with the experimental results for Rayleigh-like modes and the expectation that surface ripple is the dominant scattering mechanism for such modes. The results of this study suggest that nanodisk arrays can provide a platform for practical implementation of surface-enhanced BLS analogous to other surface-enhanced spectroscopies, and suggest the additional possibility of substantially extending the range of wave numbers in BLS through plasmonic-crystal band folding.

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