Hybrid Heterostructures of a Spin Crossover Coordination Polymer on MoS 2 : Elucidating the Role of the 2D Substrate.

Controlling the deposition of spin-crossover (SCO) materials constitutes a crucial step for the integration of these bistable molecular systems in electronic devices. Moreover, the influence of functional surfaces, such as 2D materials, can be determinant on the properties of the deposited SCO film. In this work, ultrathin films of the SCO Hofmann-type coordination polymer [Fe(py) ₂ {Pt(CN) ₄ }] (py = pyridine) onto monolayers of 1T and 2H MoS ₂ polytypes are grown. The resulting hybrid heterostructures are characterized by GIXRD, XAS, XPS, and EXAFS to get information on the structure and the specific interactions generated at the interface, as well as on the spin transition. The use of a layer-by-layer results in SCO/2D heterostructures, with crystalline and well-oriented [Fe(py) ₂ {Pt(CN) ₄ }]. Unlike with conventional Au or SiO ₂ substrates, no intermediate self-assembled monolayer is required, thanks to the surface S atoms. Furthermore, it is observed that the higher presence of Fe ³⁺ in the 2H heterostructures hinders an effective spin transition for [Fe(py) ₂ {Pt(CN) ₄ }] films thinner than 8 nm. Remarkably, when using 1T MoS ₂ , this transition is preserved in films as thin as 4 nm, due to the reducing character of this metallic substrate. These results highlight the active role that 2D materials play as substrates in hybrid molecular/2D heterostructures.
(© 2023 The Authors. Small published by Wiley-VCH GmbH.)