Tunable nano bead arrays on film for controlling propogation of light

Abstract

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 area.