Transport Phenomena in TMD-Based Heterostructures

Research on two-dimensional (2D) materials has drawn enormous attention [1,2] since the pioneering studies of the novel properties of graphene [3]. Special but not exclusive attention has been devoted to the peculiar transport properties of these systems, suitable in a variety of advanced applications, e.g., to build a new integrated circuit technology. At this extreme scale of nanoscience, with vertical dimensions of single- or few-atom-thick layers, quantum effects dominate. First-principles quantum-mechanical (QM) simulations with atomistic detail are therefore mandatory to predictively model fundamental interactions and the basic electronic and structural behavior of single material and interface units, thus making the first ladder of any multi-scale approach. By properly accounting for the atomistic grain of the material in model yet realistic structures, QM simulations can now achieve a level of accuracy that is comparable with that of experimental data, thus providing a reference that can be used for their correct interpretation and cross-validation. In this talk I will present results along this strategy, focusing on electronic transport, the family of transition metal dichalcogenides (TMD) of outstanding electronic [4] and optical [5] properties, lateral and vertical heterostructures (LH, VH) made of two TMD materials (thus, TMD2), and their potential use in FET devices. Taking the NbS2//WSe2 LH and VH systems as test cases, we conduct QM static and transport simulations on realistic models of such interfaces, and subject them to a protocol combining electrostatic potential as a unifying descriptor with fragment analysis [6] (see Figure 1). This allows us to extract few fundamental transport parameters, understand in depth the interplay of electronic structure features of the individual TMD at such interfaces, and arrive at a QM-informed rational design [7]. MoS2 VHs and 1T//2H and 1T'//2H LHs, as well as metal//graphene contacts and TMD2/support effects, will also be discussed. References: [1] Gibney E 2015 Nature 522 274-6 [2] Zhang K, Feng Y, Wang F, Yang Z and Wang J 2017 J. Mater.Chem. C 5 11992-2022 [3] Novoselov K S, et al.2004 Science 306 666-9 [4] Xu X, Yao W, Xiao D and Heinz T F 2014 Nat. Phys.10 343-50 [5] Castellanos-Gomez A 2016 Nat. Photon. 10 202-4 [6] Cusati T, Fiori G, Gahoi A, Passi V, Lemme, M C, Fortunelli A and Iannaccone G 2017 Scientific reports, 7, 1-11. [7] Golsanamlou Z, Sementa L, Cusati T, Iannaccone G, Fortunelli A (in preparation)