The study of using a multi-layered model to extract thermal property profiles of ion-irradiated materials

The thermal properties of the damaged region of ion-irradiated materials are known to change with depth in a complicated manner. As the inverse heat conduction problem is ill-posed and ill-conditioned, existing measurements are only able to obtain the thermal properties of the thin layer close to the surface or the average thermal property of the entire damaged region. In this manuscript, we studied the possibility of using a multi-layered model to demonstrate the entire damaged region and recompose a more realistic and detailed thermal property profile in the form of a piecewise function from solving thermal properties of each layer independently. Several critical factors related to the accuracy of the recomposed profile are analyzed and discussed in detail by using simulation analysis, from which the experimental guidelines and data processing procedure are summarized. The extraction accuracy of any specific parameter is found dependent on the layer discretization, sensitivity of the parameter to measurement, and experimental noise. With optimized experimental design and proper data post processing, the multi-layered model is proved capable of determining the thermal property profile with an average error of similar to 10-15%. As the experimental application, thermal conductivity profiles of ion-irradiated zirconium alloy and silicon samples are measured by using a photothermal reflectance measurement approach in the spatial- and frequency-domain. (C) 2018 Elsevier Ltd. All rights reserved.