Thermal conductivity measurement by transient thermoreflectometry using high-fluence excimer laser pulses at 248nm wavelength
Florian Döring and Hans-Ulrich Krebs
In many modern materials, thermal properties and especially the thermal conductivity become more and more important. Thus, a wide research field evolved around measuring thermal conductivities. Here, we show an implementation of a versatile transient thermoreflectometry technique for measuring thermal conductivity that utilizes a pulsed KrF laser with 248 nm wavelength and 20 ns pulse duration for pumping energy into the surface. Time resolved reflectivity changes from a continuous wave laser at 643 nm are measured using a fast Si-photodiode and an oscilloscope. To optimize this setup, thermoreflectivity properties were studied for different metal transducers as well as optical thicknesses. Since 20 ns are a comparatively long time-scale, the measurements could be fitted to an approximated analytical solution of the heat equation for thermal properties. In this way we could show that the thermal conductivities of different materials can be determined with in most cases sufficiently high accuracy by this relatively simple and flexible technique.
Keywords: Transient thermoreflectometry, thermal conductivity, pulsed laser deposition, thermoreflectivity, thermoreflectance, heat transfer.