Limitations and Advances in Optical Thermal Transport Measurements: Extremes in Properties, Length Scales, and Temperature
Thomas W. Pfeifer, Hunter B. Schonfeld, Ethan A. Scott, Henry T. Aller, John T. Gaskins, David H. Olson, Jeffrey L. Braun, Samuel Graham, Patrick E. Hopkins
Abstract
Conductive and radiative thermal transport play a critical role in the design, development, and performance of a wide array of technologies and applications. In this review, we focus on the challenges associated with nano- and microscale thermal measurements and the strategies developed thus far to overcome them. For measurements below ∼1,000°C, numerous thermoreflectance techniques are already in wide use; however, uncertainty and measurement error may limit the measurement of samples in certain regimes. These regimes include materials of high thermal conductivity (≳2,000 W/m·K), thin films (≲100 nm), or interfaces located well below the sample surface. A rigorous treatment of uncertainty and error is thus required for measuring these samples and for the development of future metrology tools. At higher temperatures, pyrometry techniques are being developed; however, several physical and experimental limitations exist. Some methods rely on a known emissivity for the measurement of temperature, and significant radiative transport can introduce error in modeling. Both of these mean that knowledge of spectrally dependent and temperature-dependent emissivity properties may be required.