Details
Speaker Name/Affiliation
Juan Sebastián Reparaz/Materials Science Institute of Barcelona, ICMAB-CSIC, Barcelona, Spain
When
-
Seminar Type
Seminar Type Other
CU Phonon Club
Location (Room)
JILA X317
Event Details & Abstracts
Monday, February 5th, @10:30am in JILA X317
featuringProf. Juan Sebastián Reparaz
Materials Science Institute of Barcelona, ICMAB-CSIC, Barcelona, Spain
Determination of the In-plane Thermal Diffusivity Using Beam-Offset Frequency-Domain Thermoreflectance with a One-Dimensional Optical Heat Source
The study of the thermal conductivity (or diffusivity) tensor (κij) in bulk and low dimensional materials has gained considerable momentum in recent years. A large number of experimental methods to study the out-of-plane components of the thermal conductivity have been developed and successfully demonstrated using different methodologies, e.g., based on electrical or optical methods. On the other hand, the study of in-plane thermal transport is comparatively more challenging due to the lack of sensitivity to this component of most developed methods, among other reasons. We demonstrate two complementary original experimental approaches with enhanced sensitivity to thermal anisotropy and in-plane heat transport, which are based on using a 1D heat source with uniform power distribution along its long axis [1,2]. We show that the 1D geometry of the heat source leads to a slower spatial decay of the temperature field as compared to 0D heat sources, hence, allowing to probe the temperature field at relatively large spatial distances from the heat source. The present approach is based on measuring the phase lag between the thermal excitation and the thermal detection spot for different excitation frequencies of the heat source, hence, rendering the thermal diffusivity of the studied samples. We have applied the previous methods to study the thermal properties of a large variety of samples, with special focus on determining the thermal conductivity tensor elements. We have investigated: β-Ga2O3 and α-Ga2O3; highly oriented pyrolytic graphite (HOPG); suspended silicon and polymer membranes with different thicknesses; bismuth, silicon, glass, AlN, GaN, ZnO, and ZnS substrates; and several Van der Waals materials such as PdSe2, hence, demonstrating their excellent performance and rather simple data analysis procedure.
References:
[1] Luis A. Pérez, Kai Xu, Markus R. Wagner, Bernhard Dörling, Aleksandr Perevedentsev, Alejandro R. Goñi, Mariano Campoy-Quiles, M. Isabel Alonso, and Juan Sebastián Reparaz, Review of Scientific Instruments 93, 034902 (2022)
[2] Kai Xu, Jiali Guo, Grazia Raciti, Alejandro R. Goni, M. Isabel Alonso, Xavier Borrise, Ilaria Zardo, Mariano Campoy-Quiles, and Juan Sebastian Reparaz, Submitted to International Journal of Heat and Mass Transfer (2023)
AND
Prof. Markus R. Wagner
Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany
Technische Universität Berlin, Institut für Festkörperphysik, Berlin, Germany
Nanoscale Origin of Thermal Conductivity Anisotropy in β-Ga2O3
Although the low thermal conductivity of β-Ga2O3 poses a challenge for high-power electronics, its large anisotropy could potentially be exploited to design structures that benefit from heat dissipation in directions of higher thermal conductivity. However, the available data on the thermal properties of Ga2O3 are exclusively related to the diffusive thermal transport regime on macroscopic length scales, while information on nanoscale thermal transport in Ga2O3 and its anisotropy is currently unavailable. In this work, we present a combined experimental and theoretical study of the thermal anisotropy of β-Ga2O3 on the macro- and nanoscale. The macroscopic anisotropy of the thermal conductivity is measured with high precision using a recently developed all-optical technique, i.e. anisotropic thermoreflectance thermometry [1], which provides sub-degree angular resolution of the in-plane thermal conductivity based on a frequency-domain thermoreflectance approach. The results are complemented by measurements of the anisotropy of the acoustic phonon velocities using polarized angle-resolved Brillouin light scattering. At the nanoscale, the thermal anisotropy is probed experimentally by angle-resolved extreme UV transient thermal grating measurements [2] using the EIS-TIMER beamline at the free-electron laser at FERMI. The experimental data are correlated with molecular dynamics calculations of the phonon frequency and mean free path dependent thermal anisotropy based on the Green-Kubo formalism including full anharmonicity [3]. Based on this joint experimental and theoretical work, we unravel the nanoscale phononic properties that give rise to the large thermal conductivity anisotropy in β-Ga2O3.
References:
[1] L.A. Pérez et al., Rev. Sci. Instrum. 93, 034902 (2022).
[2] F. Bencivenga et al., Science Advances 5, eaaw5805 (2019).
[3] C. Carbogno et al., Phys. Rev. Lett. 118, 175901 (2017).