Monolayer
![Electron microscopy of molybdenum disulfide (MoS2). The use of a MoS2 monolayer allowed clear identification of antisite (panel a) and vacancy (b) defects by the image contrast. Scale bar: 1 nm.[1]](/Images/godic/202501/28/MoS2_antisites&vacancies3533.jpg")
A monolayer is a single, closely packed layer of atoms, molecules, or cells. In some cases it is referred to as a self-assembled monolayer. Monolayers of layered crystals like graphene and molybdenum disulfide are generally called 2D materials.