In-plane thermal transport in porous nanolattice structures

Experiments and numerical simulations are conducted in this work to understand how structural porosity influences the in-plane thermal transport properties of architected alumina (Al2O3) nanolattices. Nanolattices with controlled geometry are fabricated by colloidal lithography and atomic layer deposition and suspended onto microbridge electro-thermal measurement devices. A four-probe thermal transport measurement method is used to obtain the intrinsic in-plane thermal resistance of the samples. The measured room-temperature effective in-plane thermal conductivity of three nanolattice samples decreases from 0.18 ± 0.03 to 0.07 ± 0.014 W/m K when the porosity (ϕ) increases from 80% to 87%. In comparison, the measurement values are close to 1.1 W/m K for two solid 50 nm-thick amorphous Al2O3 thin films. The measurement results of the porous nanolattice samples deviate less than 20% from both an effective medium approximation and numerical simulations that use the measured solid thermal conductivity of the non-porous alumina films and reveal negligible contribution from radiative heat transfer. The findings address a knowledge gap in the in-plane thermal transport properties of this emerging class of multifunctional thermal insulation materials.