Developing Practical Nanofabrication Techniques for Plasmonic Structures

Periodic metal nanoparticle arrays possess electromagnetic properties useful for metamaterials, light trapping, and molecular sensing, such as surface enhanced Raman spectroscopy (SERS). The localized surface plasmon resonance (LSPR) of these arrays depends on the material, periodicity, size, and spacing of nanoparticles, all features typically best controlled by traditional top down nanofabrication techniques, such as electron beam lithography. However, such fabrication methods are not realizable commercially. Bottom-up methods are increasingly being explored for alternative nanofabrication techniques in order to achieve high throughput and inexpensive fabrication. I present here multiple unique techniques for facile, inexpensive fabrication of nanostructures for biosensing. In the first technique, I fabricate 20 nm Au nanoparticle nanocluster assemblies onto a chemically functionalized diblock copolymer film, through electrophoresis and convective assembly, attaining interparticle spacings of < 1 nm. Norepinephrine is detected at 200 parts per billion using SERS, due to the high enhancement fields of the cluster. This is a cheap, high through put, and commercially accessible process. The second technique uses thermally responsive, pre stressed polyolefin (PO) film to reduce bow tie arrays by 50% in triangle area and up to 77% in tip to tip spacing, by heating in a convection oven. Reduction of the arrays shows tunability (100 nm blue shift) of the plasmon resonance, as well as potential for facile generation of hot spots for SERS. I also present work on tunable nanopillars using the polyolefin film, and on SiC nanopillar arrays, for the excitation of localized surface phonon polariton modes (SPhP), as potential low loss alternatives to plasmonics. FTIR reflectance spectroscopy measurements show the nanopillar arrays to confine infrared light with the emergence of localized SPhP modes, which exhibit dependence on pillar diameter and inter pillar spacing. Extreme light confinements and low losses are attained, with Q factors higher than the best plasmonic systems. Finally, I present work using electron beam lithography in tandem with the poyolefin film to achieve advanced plasmonic structures