A Novel Fabrication Process of Nano-Cavity Coupled Plasmonic Structures for Colormetric Sensing

Metal-insulator-metal (MIM) multilayer structures as representative plasmonic systems have been widely studied. In such a system, the metal surface can sustain bound surface plasmon polaritons (SPPs) and couple the SPPs in a dielectric cavity. Herein, a novel fabrication process, based on electron beam lithography (EBL) followed by electroplating deposition of gold, has been developed to form longitudinal metal-air-metal structures. The structures consist of a suspended top film of gold supported by an array of gold pillars and a bottom ultrathin gold film. When the gap of the two gold films is comparable to or smaller than the decay length of the interface mode, the interaction between SPPs gives rise to coupled modes which can localize the light into the insulating layer for stronger field confine and light-matter interaction. This structure exhibits vibrant reflective color at normal incident light and significant color varying with different matter filling in the nano-cavity. The sensitivity can reach 269.8 nm/RIU which offers great potential for visual and real-time biochemical detection.