Transition metal dichalcogenide monolayers

Transition metal dichalcogenide (TMDC) monolayers are atomically thin semiconductors of the type MX₂, with M a transition metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te). One layer of M atoms is sandwiched between two layers of X atoms. They are part of the large and new family of the so-called 2D materials, name used to emphasize their extraordinary thinness. For example a MoS₂ monolayer is only 6.5 Å thick.

The discovery of graphene shows how new physical properties emerge when a bulk crystal of macroscopic dimensions is thinned down to one atomic layer. Like graphite, TMDC bulk crystals are formed of monolayers bound to each other by Van-der-Waals attraction. TMDC monolayers have properties that are distinctly different from those of the semimetal graphene:

The work on TMDC monolayers is an emerging research and development field since the discovery of the direct bandgap and the potential applications in electronics and valley physics. TMDCs are often combined with other 2D materials like graphene and hexagonal boron nitride to make van der Waals heterostructure. These heterostructures need to be optimized to be possibly used as building blocks for a plenty of different devices such as transistors, solar cells, LEDs, photodetectors, fuel cells, and sensing devices. Some of these devices are already used in everyday life and can become smaller, cheaper and more efficient by using TMDC monolayers. Others are still being developed and promise to have a huge impact on our technology.

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