Three-dimensional coherent plasmonic nanowire arrays for enhancement of optical processes

Inventors

Caldwell, Joshua D. • Glembocki, Orest J. • Prokes, Sharka M. • Rendell, Ronald W.

Assignees

US Department of Navy

Abstract

A plasmonic grating sensor having periodic arrays of vertically aligned plasmonic nanopillars, nanowires, or both with an interparticle pitch ranging from λ/8-2λ, where λ is the incident wavelength of light divided by the effective index of refraction of the sample; a coupled-plasmonic array sensor having vertically aligned periodic arrays of plasmonically coupled nanopillars, nanowires, or both with interparticle gaps sufficient to induce overlap between the plasmonic evanescent fields from neighboring nanoparticles, typically requiring edge-to-edge separations of less than 20 nm; and a plasmo-photonic array sensor having a double-resonant, periodic array of vertically aligned subarrays of 1 to 25 plasmonically coupled nanopillars, nanowires, or both where the subarrays are periodically spaced at a pitch on the order of a wavelength of light.

Core Innovation

The invention provides three distinct plasmonic nanowire and nanopillar array architectures to enhance optical processes such as Raman scattering and fluorescence. These architectures include: a plasmonic grating sensor comprised of vertically aligned periodic arrays of plasmonic nanopillars or nanowires with an interparticle pitch on the order of a wavelength of light within the medium; a coupled-plasmonic array sensor with periodic arrays where interparticle gaps are sufficiently small (<20 nm) to induce overlap of evanescent plasmonic fields; and a plasmo-photonic array sensor where subarrays of 1 to 25 plasmonically coupled nanopillars or nanowires are periodically spaced at a pitch on the order of the wavelength of light, establishing a double-resonant structure that enhances optical processes while directing emitted or scattered light.

The problem solved by this invention arises from the difficulty in detecting trace levels of materials with current optical processes due to weak signals and broad, diffuse light emission. Prior art uses isolated or randomly arranged plasmonic nanoparticles, which provide high enhancement only in very localized regions with poor uniformity and reproducibility over large areas, limiting their practical use in applications requiring large-area sensing such as homeland security or defense. Existing substrates focus on maximizing local surface enhanced Raman scattering or fluorescence intensities without leveraging plasmonic coupling, long-range coupling from large arrays, or diffraction grating effects that provide directionality and reduced divergence of emitted light.

The invention overcomes these limitations by designing and fabricating large-area, periodic arrays of vertically aligned plasmonic nanopillars or nanowires that enable uniform and reproducible enhancement of optical signals alongside directional emission. The plasmonic grating sensor benefits from the periodicity to focus emission into smaller solid angles, enhancing signal collection efficiency. The coupled-plasmonic array sensor induces strong near-field plasmonic coupling with enhanced local fields and spectral tunability. The plasmo-photonic array combines these effects in a double-resonant structure, leveraging subarray plasmonic coupling and periodic spacing to simultaneously achieve large field enhancements with directional emission for improved remote sensing and emitter applications.

Claims Coverage

The patent discloses one independent claim describing a plasmonic grating sensor with specific features regarding nanopillar/nanowire arrays and interparticle pitch.

The claims collectively cover a plasmonic grating sensor featuring vertically aligned periodic arrays of plasmonic nanostructures with specified interparticle pitch forming a 2D grating, the use of plasmonic metals for the nanostructures, and the inclusion of core-shell configurations combining semiconductor or dielectric cores with metallic coatings.

Stated Advantages

Documented Applications