Quantitative Nanoscale Electrical and Thermal Transport Studies in Enhanced Thermoelectric Performance Sb₂Te₃/MoS₂ Multilayer Sample

The accurate quantitative estimation of thermal conductivity still poses a big challenge especially in the case of thin films and complex structures that are inseparable part of present-day electronics and devices. In particular, the thermal conductivity plays a major role directly affecting the performance of thermoelectric devices^[1]. This report is focussed on understanding and quantifying the role of multiple interfaces on the thermal transport in Sb₂Te₃/MoS₂ multilayer heterostructure with nanoscale layer thickness. To study both the intrinsic thermal conductivity of the heterostructure and interfacial thermal resistance between the substrate and a multilayer sample we employ a novel approach of cross-sectional scanning thermal microscope (xSThM)^[2]. In xSThM a thermal transport in a nanoscale thin small angle wedge created via Ar-Ion nanopolishing is measured via sharp temperature sensitive SThM probe. By effectively probing a range of sample thickness, the xSThM facilitates the investigation of individual contribution of the in-plane and out-of-plane thermal conductivities in the case of multi-layer samples, as well as sample – substrate thermal resistance. By exploring variation of thickness and number of layers of MoS₂ we were able to optimize the Sb₂Te₃/MoS₂ heterostructure to achieve extremely low values of in-plane and cross-plane thermal conductivity 0.5767 and 0.2401 (W/mK), respectively, along with higher values of Seebeck coefficient (619 μV/K at 347 K). A major enhancement in the value of TE performance was observed due to the effective majority carrier filtering and phonon scattering at the potential barrier present due to multiple interfaces. This study provides new insight for understanding the thermal transport in multi-layered samples, as well as other hybrid or buried nanostructures. With xSThM allowing to independently quantify in-plane, cross-plane and interfacial thermal resistance in nanoscale structures, it provides a rare approach for exploring thermal transport in thin films of complex anisotropic materials and associated devices.<br/>[1] X.-Y. Wang, H.-J. Wang, B. Xiang, L.-W. Fu, H. Zhu, D. Chai, B. Zhu, Y. Yu, N. Gao, Z.-Y. Huang, F.-Q. Zu, <i>ACS Applied Materials & Interfaces</i> <b>2018</b>, 10, 23277.<br/>[2] J. Spièce, C. Evangeli, A. J. Robson, A. El Sachat, L. Haenel, M. I. Alonso, M. Garriga, B. J. Robinson, M. Oehme, J. Schulze, F. Alzina, C. Sotomayor Torres, O. V. Kolosov, <i>Nanoscale</i> <b>2021</b>, 13, 10829.