1 research outputs found
Direct Visualization of Thermal Conductivity Suppression Due to Enhanced Phonon Scattering Near Individual Grain Boundaries
Understanding
the impact of lattice imperfections on nanoscale
thermal transport is crucial for diverse applications ranging from
thermal management to energy conversion. Grain boundaries (GBs) are
ubiquitous defects in polycrystalline materials, which scatter phonons
and reduce thermal conductivity (κ). Historically, their impact
on heat conduction has been studied indirectly through spatially averaged
measurements, that provide little information about phonon transport
near a single GB. Here, using spatially resolved time-domain thermoreflectance
(TDTR) measurements in combination with electron backscatter diffraction
(EBSD), we make localized measurements of κ within few μm
of individual GBs in boron-doped polycrystalline diamond. We observe
strongly suppressed thermal transport near GBs, a reduction in κ
from ∼1000 W m<sup>–1</sup> K<sup>–1</sup> at
the center of large grains to ∼400 W m<sup>–1</sup> K<sup>–1</sup> in the immediate vicinity of GBs. Furthermore, we
show that this reduction in κ is measured up to ∼10 μm
away from a GB. A theoretical model is proposed that captures the
local reduction in phonon mean-free-paths due to strongly diffuse
phonon scattering at the disordered grain boundaries. Our results
provide a new framework for understanding phonon–defect interactions
in nanomaterials, with implications for the use of high-κ polycrystalline
materials as heat sinks in electronics thermal management