Thermal diffusivity measurement of focused-ion-beam fabricated sample using photothermal reflectance technique.

Focused-Ion-Beam (FIB) can lift-off micrometer-sized samples from bulk materials for structural characterization and property measurement. The ability to determine thermophysical properties of such samples offers unique insight into the local microstructure-property relationship. A photothermal reflectance technique is developed to measure the thermal diffusivity of FIB-fabricated, micrometer-sized samples in this study. An analytic model is established to guide the experimental design and data analysis for the limited sample size and thickness. The thermal diffusivity of the sample can be extracted from a series of spatial-scan measurements at several modulated heating frequencies. To demonstrate the viability of the technique, a FIB-fabricated SiC plate with the size of 42 μm × 31 μm × 8 μm was used to represent high conductivity materials, which pose more challenges for the technique. The result compares favorably with literature values of SiC. The measurement uncertainty is quantified and possible experimental error sources are discussed. This technique is specially promising for thermal property measurements on nuclear fuels and materials.