Hierarchical Iridium Nanostructure-Based Thin Films with High-Temperature Stability and Oxidation Resistance for Thermocouples

It is important to expand the thermally stable temperature range of metals. Efforts must focus on tailoring the interfaces of nanostructured materials to solve this great challenge. Here, we fabricate a hierarchical columnar iridium (Ir) thin film that is thermally stable up to a temperature of 1000 °C, owing to the presence of atoms arrested by the profuse interfaces, which consume energy to retain the main columnar structure. The structural transition of thin films in the annealing process showed that the speed of oxidation and evaporation depended on the microstructure of the thin films, tailored by the interfaces between the nanocrystals. Furthermore, the hierarchical Ir thin film was applied as one arm of the thin-film thermocouple and the Pt thin film as the other arm, which exhibited excellent long-term service stability in the high-temperature range. The corresponding values of the adjusted coefficient of determination are more than 0.9999, in favor of the accurate acquisition of temperature data. A reduced deviation (0.55–0.25%) between the five calibration cycles was obtained over a wide temperature range from 300 to 1000 °C, meeting the requirements for a standard thermocouple. These results indicate that the thermal stability of thin metal films can be modified by tailoring the nanoparticle size and interfaces, thus pushing the high-temperature application of precious metal thin films in many domains.