Achieving Low-Thermal Conductivity with Inverse-Designed Nanostructures

Tuning thermal transport in nanostructures is currently done with try-and-error; while established concepts, such as phonon bottlenecks [1], may help identify promising structures, the majority of the configuration space is often left unexplored. To fill this gap, we recently introduced a framework [2] based on the adjoint gray phonon Boltzmann transport equation (BTE) to perform systematic topology optimization for nanoscale heat transport applications. In this talk, we will describe our recent efforts in extending our framework to the mode-resolved BTE, enabling a direct comparison with experiments. Our approach is based on the adjoint method and differentiable programming, which enables a fast experimentation with various objective functions. The code is implemented in the open-source code OpenBTE [3]. Length scale constraints are also included in the optimization framework, thus the optimized structures adhere to the specification of a given foundry. Several examples will be showcased, including tuning the anisotropic thermal conductivity tensor and maximizing phonon size effects. The talk will conclude with current efforts in fabricating the optimized structures.<br/>[1] G. Romano and J. C. Grossman. Phonon bottleneck identification in disordered nanoporous materials Physical Review B 96 (11), 115425<br/>[2] G. Romano and S. G. Johnson, Inverse Design in Nanoscale Heat Transport via Interpolating Interfacial Phonon Transmission. Structural and Multidisciplinary Optimization 65, 297<br/>[3] G. Romaon, OpenBTE: a solver for ab-initio phonon transport in multidimensional structures arXiv preprint arXiv:2106.02764