  Interfaces dominate heat conduction in nanostructured systems, and much work
has focused on methods to enhance interfacial conduction. These approaches
generally address planar interfaces, where the heat flux vector is everywhere
normal to the interface. Here, we explore a nanostructured interface geometry
that uses nonplanar features to enhance the effective interfacial conductance
beyond what is possible with planar interfaces. This interface consists of
interdigitating Al pillars embedded within SiO2 with characteristic feature
size ranging from 100 nm to 800 nm. The total sidewall surface area is
modulated to highlight the impact of this additional channel by changing the
pillar-to-pillar pitch L_P between 1.6 um and 200 nm while maintaining the same
Al:SiO2 fill fraction. Using optical pump-probe thermoreflectance measurements,
we show that the effective conductance of a ~65 nm thick fin layer
monotonically increases with decreasing L_P, and that the conductance for L_P =
200 nm is more than twice the prediction for a layered stack with the same
volume ratio and a planar interface. Through a combination of Boltzmann
transport modeling and finite element calculations, we explore the impact of
the pitch L_P and the pillar aspect ratio on effective thermal conductance.
This analysis suggests that the concept of nanostructured interfaces can be
extended to interfaces between diffusive and quasi-ballistic media in highly
scaled devices. Our work proposes that the controlled texturing of interfaces
can facilitate interfacial conduction beyond the planar interface regime,
opening new avenues for thermal management at the nanoscale.
