Temperature-dependent optical properties of plasmonic titanium nitride thin films

TL;DR

This study investigates how the optical properties of titanium nitride thin films change with temperature up to 900°C, revealing smaller deviations than noble metals and emphasizing the importance of temperature effects in high-temperature nanophotonics.

Contribution

The paper provides the first comprehensive analysis of the temperature-dependent dielectric functions of TiN thin films in the visible and near-infrared range up to 900°C, highlighting their stability and implications for high-temperature applications.

Findings

TiN's dielectric function deviates at high temperatures but less than noble metals.

Temperature effects significantly influence the optical response of TiN-based nanophotonic systems.

Incorporating temperature deviations improves the accuracy of optical models for high-temperature devices.

Abstract

Due to their exceptional plasmonic properties, noble metals such as gold and silver have been the materials of choice for the demonstration of various plasmonic and nanophotonic phenomena. However, noble metals' softness, lack of tailorability and low melting point along with challenges in thin film fabrication and device integration have prevented the realization of real-life plasmonic devices.In the recent years, titanium nitride (TiN) has emerged as a promising plasmonic material with good metallic and refractory (high temperature stable) properties. The refractory nature of TiN could enable practical plasmonic devices operating at elevated temperatures for energy conversion and harsh-environment industries such as gas and oil. Here we report on the temperature dependent dielectric functions of TiN thin films of varying thicknesses in the technologically relevant visible and near-infrared wavelength range from 330 nm to 2000 nm for temperatures up to 900 0C using in-situ high temperature ellipsometry. Our findings show that the complex dielectric function of TiN at elevated temperatures deviates from the optical parameters at room temperature, indicating degradation in plasmonic properties both in the real and imaginary parts of the dielectric constant. However, quite strikingly, the relative changes of the optical properties of TiN are significantly smaller compared to its noble metal counterparts. Using simulations, we demonstrate that incorporating the temperature-induced deviations into the numerical models leads to significant differences in the optical responses of high temperature nanophotonic systems. These studies hold the key for accurate modeling of high temperature TiN based optical elements and nanophotonic systems for energy conversion, harsh-environment sensors and heat-assisted applications.