VO2 Thin-Film Transducer for Steady-State Thermal Conductivity Measurements

The nonlinear properties of phase-change materials, and in particular their semiconductor-to-metal transition, enable a wide range of applications beyond the capabilities of traditional materials. Here, we develop and apply a technique to measure the thermal conductivity of solid materials by exploiting the strong optical contrast of the metallic and insulating domains of a VO2 thin-film transducer. This is achieved by steady-state imaging of the laser-induced semiconductor-to-metal transition in an optical microscope. We derive an analytical model for the radius of the observed metallic region as a function of the intensity of the focused laser beam. Fitting this model to the experimental data accurately yields the thermal conductivity of the underlying substrate, relying only on readily accessible experimental input parameters. We demonstrate this method for model samples of silica, sapphire, and silicon whose thermal conductivities span a range both below and above that of the VO2 transducer. The simplicity of the experimental setup makes it highly accessible and applicable to a wide range of bulk and thin-film materials with perspectives for spatially resolved thermal conductivity mapping.