Investigation of Plasmonics Based on Transparent Conducting Oxide

Abstract

The mid-infrared is the spectral range between 2 m and 20 m. It is useful for chemical, biological, or environmental sensing since molecules have their own absorption spectra, called fingerprints, in the mid-infrared. Surface enhanced infrared absorption is a mechanism which many mid-infrared sensors are based on. It can be usually obtained from a plasmonic resonance around a metal nano-structure. Transparent conducting oxides (TCOs) behave like a metal in the mid-infrared. TCO nano-particles are superior to metal nano-particles since the former have more strongly confined plasmonic resonance modes than the latter. Therefore, TCO nano-particle arrays may be suitable for mid-infrared sensors. This thesis theoretically investigates the characteristics of indium-tin-oxide (ITO), which is a representative TCO, nano-particle arrays. The investigated ITO nano-particle arrays can be realized by using plasma surface treatment of a polymer film and deposition of ITO on the film. The array consists of a thin ITO film, a square or hexagonal lattice of ITO circular posts, and ITO nano-spheres sitting on the posts. It is analyzed how the characteristics depend on the diameter of the ITO nano-sphere, the spacing between the adjacent ITO nano-spheres, the dimensions of the post, and the carrier concentration in ITO. The analysis demonstrates that the ITO nano-particle arrays possess strong absorption of more than 50 % in the mid-infrared. The ITO nano-particle arrays may be used as a simply-realizable, low-cost platform for mid-infrared sensors based on surface enhanced infrared absorption.