Development of a Scanning Transient Harman Method for Thermoelectric Properties Characterization

Low-dimensional nanostructures and nano-composites may demonstrate a large enhancement of the thermoelectric figure of merit ZT, therefore measurements of their thermoelectric properties are of high interest. Techniques able to screen the thermoelectric properties of a large number of samples and also to measure the spatial distribution of thermoelectric properties in a specimen are needed. This work explores a scanning transient technique for thermoelectric characterization of thin films based on the Harman method. A one dimensional theoretical model was used to investigate the appropriate experimental setup and the effect of a scanning electrode/thermal probe contacting the top surface of the specimen. Results indicate that for micrometer thick films of ZT∼1 small current values of the order of mA and electrical contact resistance below 1 Ω are necessary to minimize the Joule heating effects and to take advantage of the Peltier effect when employing the bipolar technique. A proof of concept experiment was performed on an n-type Bi₂Te₃ pellet used in a commercial thermoelectric device. The experiment lays out the strategy to extract the thermoelectric properties. Seebeck coefficient of −241 μV/K and thermal conductivity of 1.48 W/m.K were obtained from the transient Harman method when the data reduction model included energy losses through the wire. These results prelude the feasibility of the scanning technique on thin film samples.