Transition metal dichalcogenide monolayers

Transition-metal dichalcogenide (TMD or 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.

Source: Wikipedia — Transition metal dichalcogenide monolayers (CC BY-SA 4.0)