Multiresonant Anisotropic Nanostructures for Plasmon-Mediated Spectroscopies

To detect and analyze molecular species of interest, analytical sciences and technologies exploit the variation in the chemical properties associated with the analytes. Techniques involving vibrational spectroscopy rely on the unique response observed when a molecule interacts with light. Although these methods can provide the specificity needed for detection, they are traditionally hindered by the need for large quantities of material, and long acquisition times. To minimize these issues, advancements in plasmon-enhanced techniques, such as surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption (SEIRA) are being made. Such techniques make use of the strong interaction between an optical field and a metallic nanostructure to locally enhance the electromagnetic field at the surface of the nanostructure. When a molecule of interest is adsorbed onto or located near the metal surface, it is possible to amplify the vibrational fingerprint needed for chemical differentiation. To achieve the amplification necessary for sensitive and ultra-sensitive analytical measurements, the optical properties of the nanostructures must be highly tuned. In this thesis, the rational design and fabrication of a variety of anisotropic gold nanostructures capable of probing molecular systems at the monolayer level is described. An emphasis is placed on fabricating nanostructures and platforms capable of supporting multiple plasmonic resonances that span the visible through mid-infrared spectral domains. Relying on advanced nanofabrication techniques, two-dimensional arrays of metallic nanostructures were inscribed onto a variety of substrates. Once prepared, the platforms are then rigorously analyzed both numerically and experimentally to determine their physical and optical properties. An emphasis is placed on developing means of tailoring the properties to specific optical processes. Once tuned, the compatibility of the structures and platforms towards the techniques of linear dichroism, SERS, SEIRA, and correlative SERS/SEIRA measurements are examined and evaluated. This thesis offers new insight into the development of plasmonic nanostructures that exhibit multiple optical resonances, and how to tailor these resonances to specific optical processes