Interfacial ferroelectricity in marginally twisted 2D semiconductors

Abstract: Twisted heterostructures of two-dimensional crystals offer almost unlimited scope for the design of novel metamaterials. Here we demonstrate a room-temperature ferroelectric semiconductor that is assembled using mono- or few- layer MoS2. These van der Waals heterostructures feature broken inversion symmetry, which, together with the asymmetry of atomic arrangement at the interface of two 2D crystals, enables ferroelectric domains with alternating out-of-plane polarisation arranged into a twist-controlled network. The latter can be moved by applying out-of-plane electrical fields, as visualized in situ using channelling contrast electron microscopy. The interfacial charge transfer for the observed ferroelectric domains is quantified using Kelvin probe force microscopy and agrees well with theoretical calculations. The movement of domain walls and their bending rigidity also agrees well with our modelling results. Furthermore, we demonstrate proof-of-principle field-effect transistors, where the channel resistance exhibits a pronounced hysteresis governed by pinning of ferroelectric domain walls. Our results show a potential venue towards room temperature electronic and optoelectronic semiconductor devices with built-in ferroelectric memory functions.

Interfacial Ferroelectricity in Marginally Twisted 2D Semiconductors: A Detailed Overview

The paper titled "Interfacial ferroelectricity in marginally twisted 2D semiconductors" by Weston et al. explores the novel ferroelectric properties of two-dimensional (2D) semiconductors, specifically focusing on mono- or few-layer molybdenum disulfide (MoS₂) in marginally twisted configurations. The research underscores a significant advancement in the field of 2D materials, examining their potential use in next-generation electronic devices.

The study employs twisted heterostructures of MoS₂, assembled to create van der Waals interfaces with broken inversion symmetry. This configuration enables the formation of ferroelectric domains with out-of-plane polarization, a rare phenomenon in 2D materials, which can be controlled by external electric fields. The authors utilize several characterization techniques, including back-scattered electron channelling contrast imaging (BSECCI) and Kelvin probe force microscopy (KPFM), to visualize and quantify the ferroelectric domain structures and their switching behavior.

Key numerical results demonstrate the ability to move these domains through applied electric fields. The measured interfacial charge transfer aligns well with theoretical predictions, offering a promising agreement between experimental data and modeling. The study also investigates the rigidity of domain walls, emphasizing their behavior under variable conditions.

The practical implications of this research are profound. By demonstrating room-temperature ferroelectricity in a semiconducting bilayer of MoS₂, the authors open avenues for developing electronic and optoelectronic devices with integrated memory functions. Additionally, their work suggests a methodology for constructing field-effect transistors with memory retention, thereby enhancing the functionality of traditional semiconductor devices. The interplay between electrical and mechanical domain switching provides insights that could lead to the design of non-volatile memory devices and novel sensors.

Theoretically, these findings contribute to an enriched understanding of the interactions and charge polarization behaviors in 2D materials. The paper suggests that the observed ferroelectricity arises from interlayer charge transfer, driven by the asymmetric hybridization between conduction and valence bands, a significant insight for the development of functional 2D semiconductors.

Moving forward, the implications for the future of AI and optoelectronics are considerable. The integration of ferroelectric properties into 2D semiconductor devices could enable advanced computational models and contribute to the development of more efficient AI hardware infrastructures. The strong coupling dynamics in transition metal dichalcogenides (TMDs), alongside the tunable domain structures demonstrated in this paper, propose a new landscape for designing hardware that leverages quantum properties, which is essential for future technological advancements.

In summary, Weston et al. provide a comprehensive analysis of ferroelectricity in marginally twisted 2D semiconductors, revealing both theoretical and practical potential. The work forms a basis for further exploration in the field, hinting at numerous applications that remain to be fully explored in the realm of next-generation computing and electronic systems.