Improved Fabrication of Plasmonic Structures
Periodic metal nanostructure arrays possess electromagnetic properties useful for metamaterials, light trapping, and molecular sensing, such as surface enhanced Raman spectroscopy (SERS). The localized plasmon resonance frequency of these arrays depends on the material, periodicity, size, and spacing of nanoparticles. While bottom down fabrication techniques are often inexpensive and more realistic on a manufacturing scale than top down fabrication alternatives, tuning nanostructure parameters to modify optical properties is currently limited. In my work, I have demonstrated the potential for scaling down and tuning nanostructures fabricated by bottom up techniques, by using a thermally responsive polyolefin (PO) film in conjunction with nanosphere lithography (NSL). By heating the patterned substrate in a convection oven, I have successfully fabricated both nanopillar arrays with tunable dimensions, which can be used in antireflective applications, and tunable gold nanotriangle arrays, which have previously been shown to generate SERS enhancements due to the hot spots between two tips. Reductions in area as great as 95% have been achieved. Reflectance spectroscopy shows the tunabilty of the triangle array to tune the plasmon resonance. These findings are confirmed by subsequent SERS experiments. I also present here work on localized surface phonon polariton modes (SPhP), which are potential low loss alternative to plasmonics. 6H-silicon carbide nanopillar arrays are fabricated to generate localized SPhP modes, which are measured using FTIR reflectance spectroscopy and Raman spectroscopy. The measured SPhP modes are found to have exceptionally narrow line widths, giving high Q factors and low losses, and in many cases are Raman active.