Anisotropic thermoreflectance thermometry: A contactless frequencydomain thermoreflectance approach to study anisotropic thermal transport
Abstract
We developed a novel contactless frequencydomain thermoreflectance approach to study thermal transport, which is particularly convenient when thermally anisotropic materials are considered. The method is based on a lineshaped heater geometry, produced with a holographic diffractive optical element, instead of using a spot heater as in conventional thermoreflectance. The heater geometry is similar to the one used in the 3omega method, however, keeping all the technical advantages offered by noncontact methodologies. The present method is especially suitable to determine all the elements of the thermal conductivity tensor, which is experimentally achieved by simply rotating the sample with respect to the lineshaped optical heater. We provide the mathematical solution of the heat equation for the cases of anisotropic substrates, thin films, and multilayer systems. This methodology allows an accurate determination of the thermal conductivity and does not require complex modeling or intensive computational efforts to process the experimental data, i.e., the thermal conductivity is obtained through a simple linear fit ("slope method"), in a similar fashion to the 3omega method. We demonstrate the potential of this approach by studying isotropic and anisotropic materials in a wide range of thermal conductivities. In particular, we have studied the following inorganic and organic systems: (i) glass, Si, and Ge substrates (isotropic), (ii) βGa_{2}O_{3} and a Kapton substrate (anisotropic), and (iii) a 285 nm thick SiO_{2} thin film deposited on a Si substrate. The accuracy in the determination of the thermal conductivity is estimated as ≍5%, whereas the temperature uncertainty is ΔT ≍ 3 mK.
 Publication:

Review of Scientific Instruments
 Pub Date:
 March 2022
 DOI:
 10.1063/5.0066166
 arXiv:
 arXiv:2109.00763
 Bibcode:
 2022RScI...93c4902P
 Keywords:

 Physics  Applied Physics;
 Condensed Matter  Materials Science
 EPrint:
 9 pages, 6 figures