**5. Conclusions**

In this paper, we reviewed the physical mechanism of PT technique for thermal property measurement and its practical application in the thermal characterization of nanomaterials. With PT technique, the phase shift method provides a high sensitivity to the thermal properties while the amplitude method can measure thermal conductivity without considering interfacial contact. Utilizing the dependency of thermal properties on the internal structure of materials, PT technique has shown its unique capabilities for nanostructure investigation where commonly used micro-/nanoscale imaging technologies might not be applicable. Though limitations exist, PT technique is quite mature. Future application of PT technique can be extended to thermal property and structure detection beneath the surface.

**Author Contributions:** Conceptualization, S.X.; writing—original draft preparation, J.Z.; writing—review and editing, S.X. and J.L.; supervision, S.X.; funding acquisition, S.X. All authors have read and agreed to the published version of the manuscript.

**Funding:** This review work was funded by National Natural Science Foundation of China, gran<sup>t</sup> number 52106220 (for S.X.), and the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning (for S.X.).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
