Reduced thermal conductivity of ALD-grown PbTe-PbSe nano-composite thin films published in Advanced Functional Materials – Congrats Mallory DeCoster!

Mallory DeCoster’s recent work on the thermal conductivity of ALD grown PbTe-PbSe nano-composite thin films was published today in Advanced Functional Materials.

DeCoster, M.E., Chen, X., Zhang, K., Rost, C.M., Hoglund, E.R., Howe, J.M., Beechem, T.E., Baumgart, H., Hopkins, P.E., “Thermal conductivity and phonon scattering processes of ALD grown PbTe-PbSe thermoelectric thin films,” Advanced Functional Materials DOI: 10.1002/adfm.201904073 (2019).

In this work, in a collaboration with Prof. Helmut Baumgart from ODU, Dr. Thomas Beechem from Sandia, and Prof. Jim Howe from UVA, we studied the thermal conductivity of a series of thickness varying, compositionally varying PbTe-PbSe nano-structured thin films grown by atomic layer deposition.  We show that the thermal conductivity of these films exhibit glass like trends, and ultimately their thermal conductivities are dictated by the crystalline quality of the films, which can change as a function of thickness due to the ALD growth mode of the PbTe (Volmer-Weber).  This work has pronounced impact on understanding the thermal conductivity of ALD-grown thin films and their applications for thin film thermoelectric and thermal barriers.

Abstract

This work studies the thermal conductivity and phonon scattering processes in a series of n‐type lead telluride‐lead selenide (PbTe–PbSe) nanostructured thin films grown by atomic layer deposition (ALD). The ALD growth of the PbTe–PbSe samples in this work results in nonepitaxial films grown directly on native oxide/Si substrates, where the Volmer–Weber mode of growth promotes grains with a preferred columnar orientation. The ALD growth of these lead‐rich PbTe, PbSe, and PbTe–PbSe thin films results in secondary oxide phases, along with an increase microstructural quality with increased film thickness. The compositional variation and resulting point and planar defects in the PbTe–PbSe nanostructures give rise to additional phonon scattering events that reduce the thermal conductivity below that of the corresponding ALD‐grown control PbTe and PbSe films. Temperature‐dependent thermal conductivity measurements show that the phonon scattering in these ALD‐grown PbTe–PbSe nanostructured materials, along with ALD‐grown PbTe and PbSe thin films, are driven by extrinsic defect scattering processes as opposed to phonon–phonon scattering processes intrinsic to the PbTe or PbSe phonon spectra. The implication of this work is that polycrystalline, nanostructured ALD composites of thermoelectric PbTe–PbSe films are effective in reducing the phonon thermal conductivity, and represent a pathway for further improvement of the figure of merit (ZT), enhancing their thermoelectric application potential.

Funding

The authors appreciate funding from the Army Research Office, Grant No. W911NF‐16‐1‐0406. This work was supported in part by the NSF I/UCRC on Multi‐functional Integrated System Technology (MIST) Center IIP‐1439644, IIP‐1439680, and IIP‐1738752. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE‐NA0003525.