High-throughput (combinatorial) metrologies have evolved as a useful approach to rapidly determine the composition-structure-property relationships for novel materials systems as compared to the traditional one-composition-at-a-time approach. For such measurements, the combinatorial library, typically a composition-spread film, is synthesized and then characterized by high throughput measurement techniques for composition, structure and other selected properties of interest. Thus, two essential types of tools are needed: one for composition spread library film synthesis, and the other for screening of the desired property or characteristic. The success of this method applied to thermoelectric (TE) research relies on screening tools to evaluate the TE properties for a combinatorial library.
Our thermoelectric screening tool can perform temperature dependent measurements of the Seebeck coefficient, and electrical resistivity, from 300 K to 800 K. The principle of the measurement is similar to the “hot probe” technique. In this technique, a thermocouple probe is heated by a miniature heater and brought into contact with the sample surface; a local thermal gradient will be generated in the vicinity of the “hot probe”, while another thermocouple (the “cold probe”), also in contact with the surface, is placed away from the hot probe. In this embodiment, the Seebeck coefficient is measured by a differential method under steady-state conditions. Namely, a small temperature gradient (less than 5 K) is generated locally across the film held at a constant base temperature, and then the temperature difference and thermoelectric voltage are recorded to calculate the Seebeck coefficient. The Seebeck coefficient is obtained from the ratio of the thermoelectric voltage and temperature difference, both recorded by the two thermocouples. To mitigate any offset voltage interference in the Seebeck coefficient measurement, the hot probe temperature can be varied and then the Seebeck coefficient derived from the slope of a linear fit of a series of thermoelectric voltages and temperature differences.
Electrical resistance is measured by the four-probe technique in a square geometry to obtain the highest possible spatial resolution. During the test, a current is applied across the two adjacent probes and the voltage is recorded on the other two probes. By switching the polarity and combination of different probes, eight data sets of current and voltage are obtained and the corresponding resistance calculated. The resistance is averaged to cancel out any thermoelectric effect on the measurement results.