Cross-Plane Seebeck Coefficient Measurement of Misfit Layered Compounds (SnSe)_<i>n</i>(TiSe₂)_<i>n</i> (<i>n</i> = 1,3,4,5)

Abstract

We report cross-plane thermoelectric measurements of misfit layered compounds (SnSe)_n(TiSe₂)_n (n = 1,3,4,5), approximately 50 nm thick. Metal resistance thermometers are fabricated on the top and bottom of the (SnSe)_n(TiSe₂)_n material to measure the temperature difference and heat transport through the material directly. By varying the number of layers in a supercell, n, we vary the interface density while maintaining a constant global stoichiometry. The Seebeck coefficient measured across the (SnSe)_n(TiSe₂)_n samples was found to depend strongly on the number of layers in the supercell (n). When n decreases from 5 to 1, the cross-plane Seebeck coefficient decreases from -31 to -2.5 μV/K, while the cross-plane effective thermal conductivity decreases by a factor of 2, due to increased interfacial phonon scattering. The cross-plane Seebeck coefficients of the (SnSe)_n(TiSe₂)_n are very different from the in-plane Seebeck coefficients, which are higher in magnitude and less sensitive to the number of layers in a supercell, n. We believe this difference is due to the different carrier types in the n-SnSe and p-TiSe₂ layers and the effect of tunneling on the cross-plane transport.