Thermal conductivity of high-temperature Si–B–C–N thin films

In this study, thermal transport was investigated for ceramic films with different silicon, boron, carbon, and nitrogen (Si–B–C–N) compositions. In order to investigate the effect of morphology on thermal barrier properties, the microstructure of these materials was varied from amorphous to nanocrystalline. Thermal conductivity trends of several ceramic thin films were characterized with a time-domain thermoreflectance (TDTR) technique. Samples containing two different Si–B–C–N chemical compositions were created by reactive magnetron sputtering and then subjected to annealing at temperatures up to 1400 °C. The room temperature thermal conductivity of the samples prepared via a 50% Ar/50% N2 gas mixture remained constant near 1.3 W m−1 K−1, while samples prepared via a 75% Ar/25% N2 gas mixture exhibited an increase in the thermal conductivity of 2.2 W m−1 K−1 (or higher). X-ray diffraction data demonstrated that the former samples were amorphous, while the latter samples formed silicon nitride (Si3N4) crystals. The experiments reveal which Si–B–C–N film composition remains stable in the amorphous state at high temperatures, thereby retaining lower thermal transport properties. These material aspects are ideal for thermal barrier applications such as non-oxide based ceramic coatings for high-temperature protective systems of aircrafts, as well as surfaces of cutting tools and optical devices.