Stability of Thin Film Refractory Plasmonic Materials Taken to High Temperatures in Air

TL;DR

This study evaluates the high-temperature stability of refractory plasmonic materials like W, TiN, and SrRuO3, revealing their potential for robust applications and the effects of thermal cycling on their optical properties.

Contribution

It provides a comparative analysis of various refractory materials' optical stability after high-temperature annealing, highlighting TiN and TiON as promising for vacuum conditions.

Findings

SrRuO3 remains metallic after 800°C annealing

TiN and TiON's optical properties degrade due to oxidation

TiN and TiON may outperform Au and SRO in vacuum high-temperature environments

Abstract

Materials such as W, TiN, and SrRuO3 (SRO) have been suggested as promising alternatives to Au and Ag in plasmonic applications owing to their refractory properties. However, investigation of the reproducibility of the optical properties after thermal cycling at high operational temperatures is so far lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, and SrRuO3 are investigated to assess their viability for robust refractory plasmonic applications. Films ranging in thickness from 50 - 180 nm are deposited on MgO and Si substrates by RF magnetron sputtering and, in the case of SrRuO3, pulsed laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic ellipsometry, and DC resistivity. Measurements are conducted before and after annealing in air at temperatures ranging from 300 - 1000{\deg} C for one hour, to establish the maximum cycling temperature and potential longevity at temperature for each material. It is found that SrRuO3 retains metallic behaviour after annealing at 800{\deg} C, however, importantly, the optical properties of TiN and TiON are degraded as a result of oxidation. Nevertheless, both TiN and TiON may be better suited than Au or SRO for high temperature applications operating under vacuum conditions.