Atomic layer depositon (ALD) is a thin film separation method in micro- and nanotechnology.

In the process, thin films can be formed on the surface of a support by atomic layers using chemical reactions in the gas phase. In the typical design of the method, the support surface is contacted alternately with two types of support material. The surface on which the thin layer is built is therefore always exposed to the same material. A common feature of ALD procedures is that the construction of the layer is self-regulating in each step. This is typically due to the fact that there are only a finite number of “attachment points” on the surface for the molecules of the injected materials, after which the process stops after the layer has built up an atom or a molecule. Successive exposures produce a well-regulated layer structure.