Measuring Seebeck Coefficient of High Resistance 2D PtSe₂ Thin Film by Annealing Process

Seebeck coefficient serves as an important indicator for understanding the thermoelectric (TE) properties. In order to derive thermoelectric properties, it is inevitable to measure the exact Seebeck coefficient. However, in certain cases, it is very difficult to evaluate Seebeck coefficient of a 2D film with a large area when the electrical resistance is extremely large. Here, we report a simple way to measure the in-plane Seebeck coefficient of the 2D transition metal dichalcogenide (TMDC) film, whose electrical resistance is over 2 MW, through two-step thermal annealing process. By the two-step annealing at 573 K in PtSe₂ film on sapphire substrate, it is possible to obtain the effect in two ways, first, between the 2D TMDC layers, and second, interface of metal and film. As a result, we observe the electrical resistance is lowered to ~400 kW and the Seebeck coefficient is also measurable, and its value is exceeding ~160 mV/K, which is a 400% improvement compared to the single-crystalline bulk of PtSe₂. In addition, it is confirmed that the Seebeck coefficient of the annealed samples are independent of the top electrode materials. We discuss the necessity of annealing process in measuring Seebeck coefficient of having high resistance 2D PtSe₂ films by atomic crystallographic characteristics and contact resistance between metal and PtSe₂ film. Our finding is an important accomplishment in measuring and understanding the Seebeck effect and provide a promising guideline with a high TE property in 2D TMDC material.