Nanostructures Significantly Enhance Thermal Transport across Solid Interfaces

Abstract

The efficiency of thermal transport across solid interfaces presents large challenges for modern technologies such as thermal management of electronics. In this paper, we report the first demonstration of significant enhancement of thermal transport across solid interfaces by introducing interfacial nanostructures. Analogous to fins that have been used for macroscopic heat transfer enhancement in heat exchangers, the nanopillar arrays patterned at the interface help interfacial thermal transport by the enlarged effective contact area. Such a benefit depends on the geometry of nanopillar arrays (e.g., pillar height and spacing), and a thermal boundary conductance enhancement by as much as ∼88% has been measured using the time-domain thermoreflectance technique. Theoretical analysis combined with low-temperature experiments further indicates that phonons with low frequency are less influenced by the interfacial nanostructures due to their large transmissivity, but the benefit of the nanostructure is fully developed at room temperature where higher frequency phonons dominate interfacial thermal transport. The findings from this work can potentially be generalized to benefit real applications such as the thermal management of electronics.

A Review of Experimental and Computational Advances in Thermal Boundary Conductance and Nanoscale Thermal Transport across Solid Interfaces

“…Kapitza conductance is extremely dependent on the structural details of the interface at the nanoscale since the characteristic dimensions are comparable to or less than the vibrational mean‐free paths. Nanostructuring at the interface has been efficiently used to tune the energy transport pathways across interfacial regions either by introducing roughness, nonplanar features, interface mixing, or by functionalizing the interface to alter the stiffness of the bonds …”

“…Experimental works have demonstrated that nonplanar features of nanofabricated fin‐like projections with characteristic length scales of ≈100 nm can substantially increase the interfacial heat flow through an increase in the overall contact area . Similarly, MD studies have also shown that these types of features (even down to sub‐nanometer length scales) can be used to achieve an increase in h K .…”

“…One has to be careful while implementing such nanostructure engineering approaches at the interface to increase h K since Hopkins et al have shown that Ge x Si 1− x quantum dots grown on Si substrate can in fact lower h K measured across Al/Si interfaces. This is in contrast to the effect of nanopillars at interfaces between Al/Si as experimentally shown by Lee et al where nanopillar spacings in the range of ≈15–150 nm at Al/Si interfaces can drastically increase h K . It is possible that the Ge x Si 1− x alloy can lead to larger resistances due to its intrinsically lower thermal conductivity or that at some critical length scale or root‐mean‐square roughness, surface features can transition from decreasing to increasing h K .…”

“…Kapitza conductance is extremely dependent on the structural details of the interface at the nanoscale since the characteristic dimensions are comparable to or less than the vibrational mean-free paths. Nanostructuring at the interface has been efficiently used to tune the energy transport pathways across interfacial regions either by introducing roughness, [78,90,137,138] nonplanar features, [139][140][141] interface mixing, [137,142] or by functionalizing the interface to alter the stiffness of the bonds. [143][144][145][146][147][148][149][150][151] Experimental works have demonstrated that nonplanar features of nanofabricated fin-like projections with characteristic length scales of ≈100 nm can substantially increase the interfacial heat flow through an increase in the overall contact area.…”

“…[143][144][145][146][147][148][149][150][151] Experimental works have demonstrated that nonplanar features of nanofabricated fin-like projections with characteristic length scales of ≈100 nm can substantially increase the interfacial heat flow through an increase in the overall contact area. [139,140] Similarly, MD studies have also shown that these types of features (even down to sub-nanometer length scales) can be used to achieve an increase in h K . [78,141,152] This idea of nanopillars that increase the area for heat flow is analogous to the implementation of macroscale fin arrays used to increase the contact area of solids with the fluid environment.…”