Interfacial Engineering of Van der Waals Coupled 2D Layered Materials

Abstract

properties of these materials, in particular through the interlayer interactions, has opened up a new regime of materials engineering. In sharp contrast to conventional bulk materials, the interlayer interactions in van der Waals coupled materials can be controlled mainly by two approaches, that is, designing interlayer stacking configurations [7][8][9] and/or applying external fields. [10,11] The former approach relies on the relatively weak van der Waals interaction between neighboring layers. Compared with the interfaces of bulk semiconductors, where strong covalent or ionic bonds between heteroatoms lead to a well-aligned interface, van der Waals coupled materials can have various stacking configurations with different twist angle between neighboring layers. These twist structures can either be realized by direct growth methods or controlled by transfer methods. The latter approach for engineering interlayer interactions relies on the convenience to electrically gate ultrathin van der Waals coupled layers. When a gate voltage is applied along the out-of-plane direction, the displacement field between the layers can be as large as 0.3 V Å −1 . For van der Waals coupled materials, both approaches are effective in tuning their electronic, mechanical, optical properties, etc. The band structures can be easily modified, since the hybridization of the electronic states from adjacent layers significantly depends on both the stacking configuration and the out-of-plane electric field.Recent experiments have demonstrated the unusual effects of the interlayer van der Waals coupling in a number of 2D materials. For example, in bilayer graphene, by changing the relative twist angle between the two layers, van Hove singularities (vHs) emerge in its band structure. [7] Furthermore, the energy of the vHs is controllable by the twist angle. More recently, in bilayers transition metal dichalcogenide (TMDCs), the circularly polarized photoluminescence (PL) can be continuously tuned via an electrical field applied perpendicular to the 2D film. [11] Indeed, van der Waals coupling of atomically thin 2D layers is of significant promise in the contemporary material engineering. It provides us with a new path to realize high-performance electronic, photovoltaic, photonics, and optoelectronic devices, for example, field-effect transistor and light-emitting diodes based on different 2D layers stacking are designed to realize flexible and transparent electronics; [12][13][14] MoS 2 /WS 2 heterostructure can be operated as a p-n diode; [15][16][17] TMDCs/graphene was addressed as high quantum efficiency light-harvesting devices. [18][19][20] The research in 2D materials is Engineering the properties of materials is of central importance in modern science and technology. In conventional bulk materials, the property changes are realized mainly through modifying the chemical bonds and crystalline structures, or introducing dopant atoms. Recent studies in van der Waals coupled 2D layered materials have demonstrated a different way of materia...

Optical Properties of 2D Semiconductor WS2

“…2D layered materials, such as graphene and transition metal dichalcogenides (TMDs), have aroused great interest during the last decade because of their extraordinary properties for both fundamental physics and promising potential applications . Though graphene has very high mobility, there is a key bottleneck for graphene‐based transistors that its on‐off ratio is very small due to the inherent gapless band structure of graphene .…”

Abundant Active Sites on the Basal Plane and Edges of Layered van der Waals Fe3GeTe2 for Highly Efficient Hydrogen Evolution

“…van der Waals (vdW) layered materials have been known for several decades . However, the interest in these materials has been renewed since the discovery of graphene as the first two-dimensional (2D) material. , This and various other 2D materials beyond graphene have raised extensive interest in optical, electronic, and energy storage applications. − Due to intriguing properties, 2D materials are being explored as alternative electrocatalysts. − Most pristine vdW materials do not show electrochemical activity in their basal planes; thus to improve the activity of the basal plane, various surface modifications such as defect engineering, − interfacial engineering, − and doping − are required. However, if the parent layered material demonstrates activity in the basal plane prior to surface modification, its electrochemical activity can be tremendously improved after further modifications.…”

Inorganic 2D Luminescent Materials: Structure, Luminescence Modulation, and Applications

“…The number and stacking configuration of constituent layers also determine the performance of heterostructures by introducing interfacial electronic states and interlayer electronic coupling. [212,215,219,220] For example, by fabricating monolayer WS 2 on double layer graphene (2LG) instead of single layer graphene (1LG), the PL is significantly enhanced by an order of magnitude (Figure 18a), indicating that the exciton emission is affected and modulated by the underlayer number. [215] As seen from the PL spectra in Figure 18b, monolayer WS 2 on 1LG presents a broad exciton emission from the direct bandgap transition at 1.92 eV.…”