Nanoscale confinement of phonon flow and heat transport in 3D nanostructured semiconductors

Nanostructured semiconductors exhibit properties unachievable in bulk systems due to the increased influence of surfaces and interfaces. The ability to characterize and manage their thermal transport properties is critical for optimizing the performance of computer chips—however, at the nanoscale, traditional theories of heat flow break down.

Here, we probe the elastic and thermal properties of a 3D silicon metalattice, which consists of an interconnected network of nanoscale pores that dramatically alter the material properties. We impulsively heat nickel grating transducers on the sample using an infrared pump laser to launch acoustic waves and heat, which we probe using diffraction from an extreme ultraviolet probe.

We compare the experimental data to finite element models to nondestructively extract elastic properties, including porosity [1]. Using the experimentally determined porosity and elastic properties, we model heat flow in the metalattice using finite element methods and fit an apparent thermal conductivity that is two orders of magnitude below bulk silicon [2]. To understand this ultralow value, we model highly-confined heat flow using advanced theoretical tools [3]: non-equilibrium molecular dynamics, phonon hydrodynamics with a Guyer-Krumhansl transport equation, and ballistic calculations solving the Boltzmann transport equation under the relaxation time approximation.

[1] ACS AMI 14, 41316 (2022).

[2] Nano Lett. 23 (6), 2129 (2023)

[3] NPJ Comput. Mat. 11 172, (2025)