A monolayer is a single, one-atom-thick layer of material, often composed of molecules or atoms arranged in a two-dimensional structure. This thin layer can be made from various substances, including graphene, lipids, or silicon, and is significant in fields like materials science and nanotechnology. Monolayers are important for their unique properties, which differ from those of bulk materials. They can exhibit enhanced electrical, optical, or chemical characteristics, making them useful in applications such as sensors, catalysts, and drug delivery systems. Their thinness allows for efficient interactions at the molecular level.