Comprehensive analysis of the contribution from the heat capacity in thermal measurement on nanoscale thin films

Nanofilms (NFs) have been widely used in many emerging applications, such as microelectronic devices, spintronics, and optical instruments. Characterizing the thermal conductivity (k) of NFs, k(NFs), is nontrivial for both fundamental science and industrial applications. Time-domain thermoreflectance (TDTR) is a powerful technique for thermal characterizations under nano-to-micro-scales. However, both the k(NFs) and the interface thermal resistance between layers are generally unknown parameters when analyzing TDTR signals. So that an effective thermal resistance model (ETRM) is often utilized, where the impact of heat capacity of NFs, c(NFs), has been always ignored. Previous studies have proposed viewpoints on how to validate this assumption, however, which still needs to be verified further by considering the parameters' sensitivities for TDTR signals. In this work, we have highlighted the significance of sensitivity analysis for the investigation of the impact of c(NFs) with the example experiments on Ni NFs. The error of ETRM has been quantitatively and systematically studied. We found that the application requirements of ETRM in TDTR data analysis rely on the sensitivity relations between k(NFs) and interface thermal resistance. Finally, suggestions for future characterization of the k(NFs) have been discussed for reference. Our results and conclusions deepen the understanding of both the transient thermal transport process of multilayer NFs and the ability of TDTR on characterizing k(NFs).