Interface thermal transport is arguably the leading fundamental challenge for the design and implementation of advanced nanostructure technologies for energy conversion, computation, and data storage. A leading problem is multicarrier interfacial transport (electron & phonon nonequilibrium), which is distinct from the single-carrier focus of prior and ongoing research in this group and in much of the broader research community. Another challenge is when one of the media has nanoscale lateral dimensions, e.g., a nanowire contact. Both of these fundamental problems are complicated by materials (e.g., GeSbTe compounds for phase change memory) where both electrons and phonons contribute at comparable levels to the thermal conductivity.
This work generates unique experimental structures that amplify and/or modify the impact of multicarrier energy transport at interfaces. Recent work has focussed on nanocale metal-dielectric multilayers, which have technical relevance as high-performance mirrors in semiconductor error detection. For conduction normal to these mirrors, the repetitive switching from phonon dominated to electron dominated transport strongly influences both the effective thermal conductivity. Additional experiments are focused on electron transport suppression in GST and related compounds using electric fields, and the modification of carrier contributions through large temperature gradients and/or small lateral spatial dimensions. The experiments that support this work at present include picosecond and nanosecond thermoreflectance, which isolates interface resistances through the associated short diffusion lengths, as well as heating and thermometry in e-beam patterned nanobridges.