Introduction
Graphene-like materials refer to a series of two dimensional (2D) materials, sharing similar structure with graphene but with different compositions, in which atoms arrange in two dimensions with much stronger bond strength than a third dimension. The common feature of these layered materials is that the bulk 3D crystals are stacked structures. They involve van der Waals interactions between adjacent sheets with strong covalent bonding within each sheet. Since the discovery of the exotic properties of graphene, these 2D layered materials such as metal chalcogenides, transition metal oxides, and other 2D compounds have gained renewed interest (Fig 1).
Fig.1. Graphene-like Materials Series
Transition metal dichalcogenides (TMDs) consist of hexagonal layers of metal atoms (M) sandwiched between two layers of chalcogen atoms (X) with a MX2 stoichiometry (Fig 2). Depending on the combination of chalcogen (typically S, Se, or Te) and transition metal (typically Mo, W, Nb, Re, Ni, or V), TMDs occur in more than many different categories. Such materials span the entire range of electronic structures, from insulator to metal, and display interesting properties including topological insulator effect, superconductivity and thermoelectricity.
Fig.2. Crystal structure of MoS2
Applications
Graphene-like materials are perfect candidates for thinning into monolayer flakes due to their weak interlayer bonding. Because of their distinct properties and high specific surface areas, these 2D materials open up a broad range of applications such as optoelectronics, semiconductors, catalysts, chemical and biological sensors, supercapacitors, solar cells, and lithium ion batteries.
