The film material is typically deposited atom by atom on a substrate using PVD coating methods including magnetron sputtering and arc evaporation by condensation from the vapour phase to the solid phase. Due to the formation of interatomic attractive interactions, thermal mobility concerns, and surface flaws, this condensation step is not a random impingement of atoms that stick on the surface at the site of impact.
4 stages of coating growth
A four stage dynamic process typically takes place. On the surface, solitary atoms initially form a nucleus. If an atom’s migration time—which is dictated by its energy—is long enough on the surface to meet another atom before evaporating, the two atoms combine forces to form an island. Stable islands (nuclei) begin to form on the surface because the energy needed to evaporate one of the atoms from this pair is far larger than the energy needed to evaporate an individual atom. When the islands ultimately combine, the film’s development continues.
Basic simulation of coating nucleation and growth
Substrate temperature and deposition rate affect coating density
Condensed atoms do not have enough kinetic energy or surface mobility to jump over atomic steps and reach positions with a lower potential energy if the atoms are deposited on a low substrate temperature. When large deposition rates are applied, a comparable result is also seen. Adatoms are covered by other atoms before they have opportunity to choose lower energy locations.
The Thornton structure zone model
Several structural zone models have compiled the link between substrate temperature, ion kinetic energy, and deposition rate. The Thornton structural zone model (see below) is the one that is most frequently employed. This demonstrates how the coating morphology, deposition temperature, and pressure are related. The structural zone concept was further developed by Messier, Giri, and Roy in 1984.
The Thornton Structure Zone Model