Overgangsmetalldicalogenider

Overgangsmetalldicalogenider, commonly known in English as transition metal dichalcogenides (TMDCs), are layered compounds with the general formula MX2, where M is a transition metal and X is a chalcogen such as sulfur, selenium or tellurium. They form two-dimensional layers with strong in-plane covalent bonds and weak van der Waals forces between layers, enabling isolation to few- or monolayer thickness. TMDCs display a range of electronic behaviors from semiconducting to metallic and even superconducting, depending on composition and structure.

Each MX2 layer consists of a plane of metal atoms sandwiched between two planes of chalcogen atoms. The common crystal structures are 2H (hexagonal, trigonal prismatic) and 1T (tetragonal, octahedral); layer stacking and polytypism influence symmetry, band structure, and phase transitions. In monolayer form, many semiconducting TMDCs acquire a direct band gap, while the bulk typically has an indirect gap, a feature that affects optical and electronic performance.

TMDCs are prepared by mechanical exfoliation from bulk crystals, liquid-phase exfoliation, or chemical vapor deposition on substrates. Other synthesis routes include sulfurization or selenization of pre-deposited metal films or oxides to form MX2 layers. They can exist as bulk crystals, few-layer flakes, or atomically thin sheets, offering versatility for various applications.

Applications include atomically thin transistors and photodetectors, flexible and transparent electronics, and catalysis for the hydrogen evolution reaction. Some TMDCs also serve as solid lubricants or as components in van der Waals heterostructures for advanced electronics and optoelectronics.

Notable examples include MoS2, WS2, MoSe2, WSe2, MoTe2, NbS2 and TaS2.