Intrinsic Seebeck coefficients of 2D polycrystalline PtSe2 semiconducting films through two-step annealing

Abstract

Because of the high contact resistance between a metal and a film, evaluating the intrinsic Seebeck coefficient of large-area two-dimensional (2D) semiconducting films with high-resistance is challenging. Here, we report a simple scheme to measure the large-area Seebeck coefficients of 2D polycrystalline platinum diselenide (PtSe₂) thin films, whose electrical resistance (>2 MΩ) is too high to measure the thermoelectric (TE) properties, by thermal annealing. As-prepared PtSe₂ thin films deposited on sapphire substrates and treated by a two-step thermal annealing process at 574 K exhibited an intrinsic Seebeck coefficient > ∼160 μV K⁻¹, which is 400% higher than that of the single-crystalline PtSe₂ bulk, under a temperature gradient of up to 5 K along the samples. In addition, we confirm that the in-plane Seebeck coefficient of the two-step annealed samples was independent of the metal electrode. In addition, the role of thermal annealing in intrinsically-high-resistance 2D PtSe₂ semiconducting films based on the atomic-scale crystallographic characteristics of these films and the measured contact resistance between the metal and PtSe₂ layer is further discussed. Our finding represents an important achievement in understanding and measuring the Seebeck effect of high-TE-performance 2D layered transition metal dichalcogenide materials.