Insights from Ab-Initio Simulations on the Working Mechanism of Single-Layer MoS₂ Memristors

Memristors are promising building blocks for important technological applications such as high-density memory, data encryption and neuromorphic computing. In this context, 2D memristors based on atomically thin single-layer molybdenum disulfide (MoS₂) are particularly interesting due to their extremely compact size and low-power operation [1,2].<br/>Although few notable examples of working devices based on monolayer MoS₂ have been already reported in the literature, their working mechanism is still far from being understood, the main challenge being the great variability in terms of device architecture and quality of MoS₂ film. Nevertheless, regardless of the device architecture, intrinsic defects in MoS₂ are thought to be crucial for the functionality of memristors: for instance, S vacancies are highly abundant in CVD-MoS₂ and may impact non-trivially the properties at the interface with the metal contact, such as the contact resistance [3]. Moreover, in vertical Au/MoS₂/Au memristors it has been argued that the resistive switching mechanism may be due to the migration of metal atoms from the electrode to fill such S vacancies in MoS₂ [4].<br/>Here, we focus on such a device architecture and we carry out atomistic computer simulations in the framework of density functional theory (DFT). We employ surface calculations based on the Green’s function formalism [5] to construct realistic interfaces and to compute relevant properties at the interface between MoS₂and Au electrode. To elucidate the working mechanism of MoS₂ memristors, we consider defective MoS₂either with S vacancies or with Au substitution (adatoms). Then, we investigate the effect of defect concentration and defect clustering on the physics and chemistry of MoS₂ interfaces. By exploring several possible case scenarios, we were able not only to better understand the pivotal role of the extra Au atoms for the resistive switch mechanism of MoS₂ memristors, but also to provide the theoretical justification on experimental findings.<br/><br/>[1] EU H2020 NeurONN Project, www.neuronn.eu.<br/>[2] Horizon EU PHASTRAC Project, https://phastrac.eu.<br/>[3] G. Boschetto et al. “Ab Initio Computer Simulations on Interfacial Properties of Single-Layer MoS₂ and Au Contacts for Two-Dimensional Nanodevices” ACS Appl. Nano Mater.,5, 1092-10202, <b>2022</b>.<br/>[4] R. Ge et al., “Atomristor: Nonvolatile Resistance Switching in Atomic Sheets of Transition Metal Dichalcogenides,” <i>Nano Lett.</i>, 18, 434-441, <b>2017</b>.<br/>[5] S. Smidstrup et al. “First-Principles Green’s Function Method for Surface Calculations: A Pseudopotential Localized Basis Set Approach,” Phys. Rev. B, 96, 195309, <b>2017</b>.