Thickness-Independent Vibrational Thermal Conductance across Confined Solid-Solution Thin Films

We experimentally show that the thermal conductance across confined solid-solution crystalline thin films between parent materials does not necessarily lead to an increase in thermal resistances across the thin-film geometries with increasing film thicknesses, which is counterintuitive to the notion that adding a material serves to increase the total thermal resistance. Confined thin epitaxial Ca0.5Sr0.5TiO3 solid-solution films with systematically varying thicknesses in between two parent perovskite materials of calcium titanate and (001)-oriented strontium titanate are grown, and thermoreflectance techniques are used to accurately measure the thermal boundary conductance across the confined solid-solution films, showing that the thermal resistance does not substantially increase with the addition of solid-solution films with increasing thicknesses from similar to 1 to similar to 10 nm. Contrary to the macroscopic understanding of thermal transport where adding more material along the heat propagation direction leads to larger thermal resistances, our results potentially offer experimental support to the computationally predicted concept of vibrational matching across interfaces. This concept is based on the fact that a better match in the available heat-carrying vibrations due to an interfacial layer can lead to lower thermal boundary resistances, thus leading to an enhancement in thermal boundary conductance across interfaces driven by the addition of a thin vibrational bridge layer between two solids.

Automated summary

Experimental results show that thermal resistance may not increase with the addition of confined solid-solution films of varying thicknesses between parent materials. This contradicts the conventional understanding that adding more material leads to larger thermal resistances. The results potentially support the concept of vibrational matching across interfaces, suggesting that adding a thin vibrational bridge layer between two solids could enhance thermal boundary conductance.