Plasmonic resonances in nanostructured transparent conducting oxide films

TL;DR

This study explores the nanoscale patterning of transparent conducting oxides (TCOs) to harness their plasmonic properties in the near-infrared, demonstrating their potential as low-loss metal substitutes in plasmonic devices.

Contribution

It introduces a nanopatterning process for TCOs using lift-off and electron-beam lithography, enabling the fabrication of plasmonic nanostructures with tunable resonances.

Findings

TCO nanodisks exhibit collective electron oscillations in the 1.6-2.1 micron range.

Resonance peaks can be tuned by doping levels and thermal annealing.

TCOs show promise as low-loss plasmonic materials in the NIR regime.

Abstract

Transparent conducting oxides (TCO) are emerging as possible alternative constituent materials to replace noble metals such as silver and gold for low-loss plasmonic and metamaterial (MMs) applications in the near infrared (NIR) regime. The optical characteristics of TCOs have been studied to evaluate the functionalities and potential of these materials as metal substitutes in plasmonic and MM devices, even apart from their usual use as electrode materials. However, patterning TCOs at the nanoscale, which is necessary for plasmonic and MM devices, is not well-studied. This paper investigates nanopatterning processes for TCOs, especially the lift-off technique with electron-beam lithography, and the realization of plasmonic nanostructures with TCOs. By employing the developed nanopatterning process, we fabricate 2D-periodic arrays of TCO nanodisks and characterize the material's plasmonic properties to evaluate the performance of TCOs as metal substitutes. Light-induced collective oscillations of the free electrons in the TCOs (bulk plasmons) and localized surface plasmon resonances are observed in the wavelength range from 1.6 to 2.1 micron. Well-defined resonance peaks are observed, which can be dramatically tuned by varying the amount of dopant and by thermally annealing the TCO nanodisks in nitrogen gas ambient while maintaining the low-loss properties.