(Invited) Thermoelectric Transport in Nanostructured 3D Topological Insulators and Stacked 2D Materials / Ferecrystals

Abstract

Research in thermoelectric (TE) quantum structures was greatly propelled by the pre[1]diction in the early 1990s of a significant boost in TE efficiency by quantum size effects. Recently, research interest has shifted from quantum size effects in conventional semiconductors toward new types of quantum materials (e.g., topological insulators [TIs], Weyl and Dirac semimetals) characterized by their nontrivial electronic topology. Bi2Te3, Sb2Te3, and Bi2Se3, established TE materials, are also TIs exhibiting a bulk bandgap and highly conductive and robust gapless surface states. The signature of the nontrivial electronic band structure on the TE transport properties can be best verified in transport experiments using nanowires and thin films. However, even in nanograined bulk, the typical peculiarities in the transport properties of TIs can be seen. The signature of TI surface states on the thermoelectric properties of nanowire model systems will be discuss in depth and how these states can be modified by chemical modifications and in the vicinity of magnetic insulators.In the second part, we will report a different material class of stacked 2D materials based on metal monochalcogenides (MMCs), topological insulators and non-van der Waals (nvW) 2D Materials called ferecrystals via atomic layer deposition (ALD). The ferecrystals can be tailored to exhibit unusual properties such as low thermal conductivity or electronic or magnetic properties. The electronic properties of the 2D materials are modified by the interactions between the interwoven layered and non-layered materials. We have developed ferecrystal combinations, where the 2D material is the electronically active or in-active layer by selection of the bandgap for each layer. Figure 1