Atomic layer lithography of plasmonic nanogaps for enhanced light-matter interactions: fabrication and applications

Abstract

Enhanced light-matter interactions at the nanometer scale have many potential applications, such as thin film sensing, enhanced Raman scattering, enhanced infrared absorption, particle manipulation, among others. Metal – insulator – metal nanogap structure is one of the most effective plasmonic devices for such applications since they are capable of generating the strongest light field enhancement inside the nanogap. However, current techniques to make such nanogap structures are either very expensive, slow, or lacking of control over nanogap size, pattern shape, and position. In this thesis, two wafer-scale fabrication methods are presented to address the challenges in fabrication. The fabricated devices are then used to demonstrate the above-mentioned applications. Atomic layer deposition is used in both methods to define the width of nanogap with angstrom resolution. The length, position, and shape of the nanogaps are precisely controlled in wafer scale by photolithography and metal deposition. A simple tape peeling and a template stripping process are used to expose the nanogaps. Nanogap devices with different designs are proved to support strong optical resonances in visible, near infrared, mid infrared, and terahertz-frequency regimes. By squeezing electromagnetic waves into nanometer wide gaps, huge field enhancement can be achieved inside the gaps. These novel fabrication methods can easily be duplicated and thus lead to broad studies and applications of the enhanced light-matter interactions.