Abnormal Seebeck Effect in Vertically Stacked 2D/2D PtSe₂/PtSe₂ Homostructure

Abstract

When a thermoelectric (TE) material is deposited with a secondary TE material, the total Seebeck coefficient of the stacked layer is generally represented by a parallel conductor model. Accordingly, when TE material layers of the same thickness are stacked vertically, the total Seebeck coefficient in the transverse direction may change in a single layer. Here, an abnormal Seebeck effect in a stacked two-dimensional (2D) PtSe 2 /PtSe 2 homostructure film, i.e., an extra in-plane Seebeck voltage is produced by wet-transfer stacking at the interface between the PtSe 2 layers under a transverse temperature gradient is reported. This abnormal Seebeck effect is referred to as the interfacial Seebeck effect in stacked PtSe 2 /PtSe 2 homostructures. This effect is attributed to the carrier-interface interaction, and has independent characteristics in relation to carrier concentration. It is confirmed that the in-plane Seebeck coefficient increases as the number of stacked PtSe 2 layers increase and observed a high Seebeck coefficient exceeding ≈188 μV K −1 at 300 K in a four-layer-stacked PtSe 2 /PtSe 2 homostructure.

Anomalous thermal transport of vertically stacked PtSe2 thin films with interface formation

“…This observation is associated with the O 2 plasma treatment of the lower PtSe 2 thin film. According to our previous reports, 44,45 Pt- and Se-deficient atomic vacancies were observed on the top layers of O 2 plasma-treated PtSe 2 thin films, contributing to the formation of interfaces in vertically stacked PtSe 2 /PtSe 2 homostructures.…”

“…These results demonstrate that the high S ‖ and PF ‖ values of the 3-stacked PtSe 2 /PtSe 2 homostructure in the entire temperature range can be attributed to the additional Seebeck effect at the interface between the PtSe 2 layer caused by the hot-carrier injection from the lower layer to the upper layer under the applied temperature gradient along the samples. 20,23…”

“…The semiconductor-to-semimetal transition characteristics of 2D PtSe 2 offer a promising avenue for enhancing the power factor of TE devices, which is achieved by simultaneously enhancing the S and σ , 17,20,22,23 contrary to the usual relationship between these two parameters. In more specific terms, Moon et al demonstrated the gate-modulated TE properties ( σ and S ) of PtSe 2 thin films with thicknesses of bilayers, 4.6 and 19.4 nm, by exfoliating a PtSe 2 single crystal (1T phase) at temperatures of 30, 100, 200, and 300 K, respectively.…”

“…17 Upon comparison of the data, it was observed that the PtSe 2 thin film with a thickness of 4.6 nm exhibited a simultaneous increase in σ and S with increasing temperature up to 300 K. This phenomenon is attributed to that metallic and semiconducting characteristics coexist inside the semimetallic PtSe 2 thin film. 17,24 Moreover, Lee et al reported the interface-induced Seebeck effect in vertically stacked 2D/2D PtSe 2 /PtSe 2 homostructures at room temperature, 20,23 which played a crucial role in increasing both the S and σ of the sample simultaneously. In these instances, the interface formation between the PtSe 2 layers results in an increase in the PF, attributed to the generation of additional S through the interfaces, with σ remaining almost identical to that of the PtSe 2 unit layer.…”

Axis dependent conduction polarity in the air-stable semiconductor, PdSe2

“…In addition, such materials would enable a systematic understanding of the interplay between band structure, doping levels, and dopant activation energies on ADCP. Here, we show that PdSe 2 , one member in a family of precious metal transition metal dichalcogenides that have attracted considerable recent interest, 19–26 satisfies all these requirements and is an ideal model system for understanding the emergence of ADCP in semiconductors. Through the growth and characterization of the anisotropic transport properties of PdSe 2 single crystals with extrinsic p-type Ir and n-type Sb dopants in the range of 10 16 –10 18 cm −3 we show that this material exhibits ADCP at temperatures for which there is a sufficient concentration of both majority and minority carriers.…”