Fabrication of holographically featured nanostructures for surface-enhanced raman scattering applications

Abstract

Holographic lithography (HL) has been developed to produce a large variety of defect-free three-dimensional (3D) periodic nanostructures over large areas. To fabricate such nanostructures, the optical interference among multiple coherent beams is transferred into photoresist. However, conventional multi-beam HL requires complex optical setup composed of beam splitters, mirrors, and polarizers with elaborate alignment. To overcome such shortcomings, prism is employed for laser beam splitting and recombination; this prism HL provides simple and rapid method to create periodic nanostructures.Meanwhile, surface enhanced Raman scattering (SERS) has been emerged as one of the powerful strategies for fast detection of characteristic “fingerprint” signatures of numerous chemical and biological molecules. The SERS is derived from strong electromagnetic (EM) field enhancements at the surface of metallic nanoparticles or nanoarrays by the plasmonic resonance. To fabricate SERS-active metallic nanostructures, a variety of techniques have been developed, which enable to design the optimal geometric features for sensing applications. However, simultaneous achievement of high reproducibility and large-scale sample homogeneity while maintaining high sensitivity still remains an important challenge.Here, I describe the multipurpose prism HL-featured 3D periodic nanostructures which provide uniform and reproducible 2D/3D SERS substrates. In Chapter 1, I briefly introduce the principle of prism HL technique and SERS phenomena. One lesson from Chapter 1 is metallic structures which possess nano-sized gaps or sharp corners provide high Raman signal enhancement; this is contributed from the locally-enhanced magnitude of EM fields at those gaps or corners. To engineer the nanogaps in metallic nanostructure, I have developed novel method for fabricating uniformly-ordered plasmonic arrays with controllable nanogaps. In Chapter 2, I report the method and unique optical properties of th...