In-Plane Seebeck Coefficients of Thickness-Modulated 2D PtSe₂ Thin Films

Abstract

Two-dimensional (2D) PtSe 2 is rapidly emerging as a promising candidate for developing devices that exhibit a significantly enhanced thermoelectric power factor because of its thickness-modulation-induced tunable semiconductor-to-semimetal transition characteristic. This interesting phenomenon motivated us to measure the in-plane Seebeck coefficients and electrical conductivities of large-area 2D PtSe 2 thin films with approximately 2−15 nm thicknesses. We observed an outstanding in-plane Seebeck coefficient of ∼73.7 μV/K and a high electrical conductivity of ∼216 S/cm in the 9-nm-thick 2D PtSe 2 film than in the ∼6-nm-thick 2D PtSe 2 film at 300 K. Our observations suggest that thickness-dependent semiconductor-to-semimetal transitions in PtSe 2 -based materials offer a distinguishable advantage for enhancing the power factor of 2D PtSe 2 -based thermoelectric devices.

Thickness-Dependent In-Plane Thermoelectric Properties of PtTe2 with n-Type Conduction

“…In particular, the E g mode is red-shifted by 113.4 cm –1 in the thicker PtTe 2 (≥20 nm) films. The A 1g /E g ratios are gradually reduced with increasing PtTe 2 film thickness owing to the enhancement in the out-of-plane interactions among the increasing number of layers in the thicker films . The thickness-dependent Raman characteristic is consistent with those reported previously − and confirm the complete tellurization of the Pt films into 2D PtTe 2 thin films.…”

“…As shown in Figure g, the in-plane power factors (PF ∥ ) for the ∼5, ∼10, ∼20, and ∼30 nm thick 2D PtTe 2 films were calculated to ∼0.02, ∼2.35, ∼6.11, and ∼13.40 μW/mK 2 , respectively. Based on these results, the higher S ∥ and PF ∥ values in the ∼20 and ∼30 nm thick 2D PtTe 2 thin films are believed to be related to the more semimetallic transition as the PtTe 2 film thickness increases. , …”

“…More detailed experimental setup can be found in the previous literature. 12 A temperature gradient was applied with a strain gauge from right to left in a direction parallel to the sample surface. The size of each transferred 2D PtTe 2 thin film was 3 mm × 8 mm (width × length).…”

“…The electrical properties of the PtTe 2 thin films were evaluated using the Hall measurement method. The in-plane Seebeck coefficients of these films were evaluated by linearly fitting the plot of Δ V versus Δ T using S ∥ = −Δ V ∥ /Δ T (where S ∥ is the in-plane Seebeck coefficient, Δ V is the voltage difference, and Δ T is the temperature difference) . These in-plane TE properties of the thickness-modulated 2D PtTe 2 thin films are anticipated to offer an alternative approach for fabricating high-efficiency TE devices comprising vertically stacked 2D/2D heterostructures (i.e., PtTe 2 /MoS 2 and PtTe 2 /PtSe 2 ).…”

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

“…This result is attributed to the dependence of semiconductor‐to‐semimetal transition on increasing the thickness of the PtSe 2 materials. For instance, we confirmed the semi‐metallic behavior of PtSe 2 thin films (≈6 nm) [ 23–24 ] by measuring the relationship between the electrical conductivity and temperature, corresponding well with the theoretical calculation. The theoretical calculation shows that a monolayer PtSe 2 is a semiconductor with a band gap up to ≈1.2 eV, and the band gap of the PtSe 2 rapidly reduces and becomes zero from the four‐layer PtSe 2 .…”