Simultaneous measurement of in-plane and through-plane thermal conductivity using beam-offset frequency domain thermoreflectance

Abstract

Transient thermoreflectance (TTR) techniques are ubiquitous methods for measuring thermal conductivity of bulk materials and thin-films. Both through-plane thermal conductivity k and in-plane thermal conductivity k should be independently measured in transversely anisotropic materials. When these properties are measured using conventional TTR techniques, the accuracy of the k measurement is dependent on the accuracy of measuring k and vice versa. This is especially problematic for thin-films measurements as uncertainty in k (∼5%) can propagate and grow for uncertainty in k. In this paper, we present a method for the simultaneous measurement of k and k using beam-offset frequency domain thermoreflectance (FDTR) with robust uncertainty estimation. The conventional diffusive heat transfer solution is analyzed to show that offset and heating frequency can independently control the sensitivity to directional thermal conductivity and extract values for k and k. Numerical uncertainty analyses demonstrate that sweeping both heating frequency and beam offset results in a reduction of measurement uncertainty. This modified measurement technique is demonstrated on crystalline alumina (c-AlO), amorphous alumina (a-AlO), quartz, fused silica, and highly oriented pyrolytic graphite.

Measuring the thermal properties of anisotropic materials using beam-offset frequency domain thermoreflectance

“…Despite the importance of inplane heat transport in 2D materials, there are only a few reports that demonstrate the determination of anisotropic thermal conductivity using FDTR. 3,5,14,20 These rely on either working with small spot sizes 3,5,14 or on beam offsetting. 20 However, if the experimental parameters are not associated with sufficiently high sensitivities, or the measurements do not span a sufficiently wide parametric range, the results can be plagued with relatively large error bars.…”

“…3,5,14,20 These rely on either working with small spot sizes 3,5,14 or on beam offsetting. 20 However, if the experimental parameters are not associated with sufficiently high sensitivities, or the measurements do not span a sufficiently wide parametric range, the results can be plagued with relatively large error bars. 20 In this paper, we present a beam-offset FDTR (BO-FDTR) approach in which we combine the schemes outlined above in order to measure the thermal conductivity anisotropy and TBC from a single data set obtained at multiple beam offsets.…”

“…3,21 In BO-FDTR, the maximum reported modulation frequency is only 6 MHz because the signal strength further decays when the probe beam samples only a portion of the thermal footprint given by the pump beam. 20 Here, we use spot sizes of about 1.4 lm, which yield high enough signals to allow measurements up to 50 MHz at large beam offset values without the need of heterodyne measurement techniques. The coherent RF noise at high modulation frequencies can be reduced when necessary by taking reference noise measurements concurrently and subtracting the noise from the thermal signal, avoiding more complicated techniques such as heterodyning.…”

Probing Anisotropic Thermal Conductivity of Transition Metal Dichalcogenides MX2 (M = Mo, W and X = S, Se) using Time‐Domain Thermoreflectance

“…Several techniques could potentially be applied to measure anisotropic thermal conductivities, 29 including the steady-state method, 30 3ω method, 31 time-domain thermoreflectance (TDTR) 32 and frequency-domain thermoreflectance (FDTR) methods. 33 However, they all have their own challenges. For instance, the small sample thickness makes it very challenging to measure the through-plane thermal conductivity of TMDs using the steady-state method, 30 while the requirement of a large and flat sample surface hinders the implementation of the 3ω method.…”

Anisotropic Thermoreflectance Thermometry: A contactless frequency-domain approach to study anisotropic thermal transport

“…The development of novel experimental methodologies to study anisotropic thermal transport has recently become a relevant research objective. A considerable number of experimental techniques and methodologies 9,[14][15][16][17][18][19][20][21][22][23][24][25][26][27] based on variations of the 3-omega method, 28 time-domain thermoreflectance, 29 and frequency-domain thermoreflectance 30 have been developed for this purpose, demonstrating their capability to obtain the components of κ i j . The main differences between these approaches are the dimensionality of the heat source (line or spot), and their contact or contactless fashion (electrical resistor or focused optical spot).…”