A new spatial-domain thermoreflectance method to measure a broad range of anisotropic in-plane thermal conductivity

•Accurate measurements of a broad range of in-plane thermal conductivity from 1-2000 W/(m•K) with a typical uncertainty of 10W/(m·K). In this work, a new spatial-domain thermoreflectance (SDTR) method has been developed to measure a broad range of kin of millimeter-scale small samples, including those lacking in-plane symmetry, extending the current limit of the measurable kin to as low as 1 W/(m·K). This SDTR method establishes a new scheme of measurements using the optimized laser spot size and modulation frequency and a new scheme of data processing, enabling measurements of in-plane thermal conductivity tensors of a broad range of kin values with both high accuracy and ease of operation. Some details such as the requirement on the sample geometry, the effect of the transducer layer, and the effect of heat loss are also discussed. As a verification, the kin of some transversely isotropic reference samples with a wide range of kin values including fused silica, sapphire, silicon, and highly ordered pyrolytic graphite (HOPG) have been measured using this new SDTR method. The measured kin agree perfectly well with the literature values with a typical uncertainty of