We demonstrate the fabrication of a highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles for plasmonic enhancement. The average enhancement effect is evaluated by measuring the spectral broadening effect caused by self-phase-modulation. The nonlinear refractive index <i>n<sub>2</sub></i> was measured to be 7.0917×10<sup>-19</sup> m<sup>2</sup>/W for a waveguide whose <i>W<sub>open</sub></i> is 5 μm. Several waveguides at different locations on one wafer were measured in order to take the randomness of the nanoparticle distribution into consideration. The largest enhancement is measured to be as high as 10 times. Fabrication of this waveguide started with a MEMS grade photomask. By using conventional optical lithography, the wide linewidth was transferred to a <100> wafer. Then the wafer was etched anisotropically by potassium hydroxide (KOH) to engrave trapezoidal trenches with an angle of 54.7º. Side wall roughness was mitigated by KOH etching and thermal oxidation that was used to generate a buffer layer for silicon nitride waveguide. The guiding material silicon nitride was then deposited by low pressure chemical vapor deposition. The waveguide was then patterned with a chemical template, with 20 nm gold particles being chemically attached to the functionalized poly(methyl methacrylate) domains. Since the particles attached only to the PMMA domains, they were confined to localized regions, therefore forcing the nanoparticles into clusters of various numbers and geometries. Experiments reveal that the waveguide has negligible nonlinear absorption loss, and its nonlinear refractive index can be greatly enhanced by gold nano clusters. The silicon nitride trench waveguide has large nonlinear refractive index, rendering itself promising for nonlinear applications.
Periodic arrays of sub-wavelength structures have garnered significant interest for surface enhanced Raman
spectroscopy (SERS) and metal enhanced fluorescence (MEF), and for anti-reflective coating properties. For SERS
and MEF, coupling metal nanoparticles with nanometer scale spacing can induce strong local electromagnetic field
enhancements at the plasmon resonance, significantly increasing the Raman signal or fluorescence of a molecule.
Inspired by moth eyes, metal nanoparticle arrays can reduce the reflection of incident light, shown useful for
improving the efficiency of solar cells. Here, we present fabrication of robust, tunable, inexpensive and quickly
reproducible gold coated, nanopillar arrays for applications in enhancing Raman/fluorescence signals or antireflective
surfaces for efficient solar cells. To create homogenous metallic nanostructures with controllable sizes and
interparticle spacings, we have integrated conventional nanosphere lithography techniques with thermally
responsive polyolefin (PO) films. Spin coating 500 nm PS beads onto PO substrates, followed by oxygen plasma
etching, is used to vary the size and periodicity of the resulting PS nanopillar bead array. A 50 nm thick gold film
can then be added using chemical vapor deposition (CVD). Nanostructures were characterized with scanning
electron microscopy and atomic force microscopy. When heated from room temperature up to 115oC, structures on
PO films undergo a reduction in feature size and interparticle spacing by up to 35 % in length and 50% in surface