Moiré superlattice engineering of two-dimensional materials for electrocatalytic hydrogen evolution reaction

As a combination concept of a 2D material and a superlattice, two-dimensional superlattices (2DSs) have attracted increasing attention recently. The natural advantages of 2D materials in their properties, dimension, diversity and compatibility, and their gradually improved technologies for preparation and device fabrication serve as solid foundations for the development of 2DSs. Compared with the existing 2D materials and even their heterostructures, 2DSs relate to more materials and elaborate architectures, leading to novel systems with more degrees of freedom to modulate material properties at the nanoscale. Here, three typical types of 2DSs, including the component, strain-induced and moiré superlattices, are reviewed. The preparation methods, properties and state-of-the-art applications of each type are summarized. An outlook of the challenges and future developments is also presented. We hope that this work can provide a reference for the development of 2DS-related research.

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Preparation, properties and applications of two-dimensional superlattices.

Layered 2H-molybdenum ditelluride (MoTe2) is a promising near-infrared material with optical activity, which enables hybrid-integrated with silicon photonics for communication purposes. The use of various artificial hetero-stacking or twist-stacking techniques can further expand the emission bandwidth and offer more choices of optical-active materials used as building blocks in on-chip optoelectronic devices. However, while the twisting technique is an effective tool for adjusting interlayer interaction in van der Waals materials, a systematic experimental study of twisted MoTe2 homobilayers is currently lacking. Here, a series of MoTe2 homobilayers were prepared with precisely controlled twist-angles from 0° to 60°, with a particular focus on the small-twist region. Conducting photoluminescence measurements at low temperatures enabled observation of the evolution of exciton emission as the twist angle increases. Neutral and charged excitons were also identified in a dual-gated 1.4° twisted MoTe2 through gate-dependent and field-dependent photoluminescence measurements. Furthermore, spatially-resolved photoluminescence measurements revealed the critical role of the interface conditions, including interlayer spacing and strain, in addition to the twist-angle, in determining the excitonic behavior of the material. This study provides compelling experimental evidence for understanding the twist-angle-dependent excitonic behaviors in atomically thin semiconductors. 

Feiyue Wang

Papers

Preparation, properties and applications of two-dimensional superlattices.

Exciton Emission in Molybdenum Telluride Homobilayers with Fine‐Tuned Twist‐Angles