Thermal Conductance of Nanoscale VO$_{x}$ Epitaxial Layers

We use time-domain thermoreflectance to measure the thermal conductance of VO$_{x}$ layers in epitaxial Pt/VO$_{x}$/Pt structures. In particular, the metal-insulator-transition of VO$_{2}$ at $\approx $70$^{\circ}$C allows us to systematically explore channels for heat transport between metals and correlated-electron systems. Pt/VO$_{x}$/Pt layers are deposited on a sapphire substrates by reactive DC sputtering with O2 partial pressure varied from 0{\%} to 13{\%}. The thermal conductance has a strong dependence on thickness, 3-50 nm, and oxygen content, pure V to V$_{2}$O$_{5}$. The thermal conductance of $\sim $10 nm thick layers of V in series with the two Pt/V interfaces is 1 GW/m$^{2}$-K, comparable to what is expected based on the diffuse-mismatch model for electron transport at interfaces. The conductance of $\sim $10 nm thick layers of VO$_{2}$ at room temperatures is remarkably high, 0.5 GW/m$^{2}$-K, for the series conductance of two metal-dielectric interfaces. At the metal-insulator-transition, the conductance of VO$_{2}$ layers increases by only 10{\%}, indicating that electrons in Pt and electrons in metallic VO$_{2}$ are not strongly coupled.