A microprobe technique for simultaneously measuring thermal conductivity and Seebeck coefficient of thin films

We demonstrate a microprobe technique that can simultaneously measure thermal conductivity kappa and Seebeck coefficient alpha of thin films. In this technique, an alternative current joule-heated V-shaped microwire that serves as heater, thermometer and voltage electrode, locally heats the thin film when contacted with the surface. The kappa is extracted from the thermal resistance of the microprobe and alpha from the Seebeck voltage measured between the probe and unheated regions of the film by modeling heat transfer in the probe, sample and their contact area, and by calibrations with standard reference samples. Application of the technique on sulfur-doped porous Bi2Te3 and Bi2Se3 films reveals alpha=-105.4 and 1.96 mu V/K, respectively, which are within 2% of the values obtained by independent measurements carried out using microfabricated test structures. The respective kappa values are 0.36 and 0.52 W/mK, which are significantly lower than the bulk values due to film porosity, and are consistent with effective media theory. The dominance of air conduction at the probe-sample contact area determines the microscale spatial resolution of the technique and allows probing samples with rough surfaces.