During evaporation coating, the nucleation and growth of the film layer are the basis of various ion coating technology
1.Nucleation
In vacuum evaporation coating technology,after the film layer particles are evaporated from the evaporation source in the form of atoms, they fly directly to the workpiece in high vacuum and form the film layer by nucleation and growth on the surface of the workpiece. During vacuum evaporation, the energy of film layer atoms escaping from evaporation source is about 0.2eV. When the cohesion between the particles of the film layer is greater than the bonding force between the atoms of the film layer and the workpiece,form an island nucleus. A single film layer atom stays on the surface of the workpiece for the duration of time doing irregular movement, diffusion, migration, or collision with other atoms to form atomic clusters The number of atoms in the atomic cluster reaches a certain critical value, a stable nucleus is formed, called a homogeneous shaped nucleus.
smooth, and contains many defects and steps, which causes the difference in the adsorption force of different parts of the workpiece to the radioactive atoms. The adsorption energy of the surface of the defect is greater than that of the normal surface, so it becomes the active center, which is conducive to preferential nucleation, called heterogeneous nucleation. When the cohesive force is equal to the binding force, or the binding force between the membrane atoms and the workpiece is greater than the cohesive force between the membrane atoms, the lamellar structure is formed. In ion plating technology, island core is formed in most cases.
2.Growth
Once the core of the film is formed, it continues to grow by trapping the incident atoms.The islands grow and combine with each other to form larger hemispheres, gradually forming a hemispherical island layer that spreads over the surface of the workpiece.
When the atomic energy of the film layer is high, it can diffuse sufficiently on the surface and a smooth continuous film can be formed when the subsequent incoming atomic clusters are small.If the diffusion of the atoms on the surface is weak and the size of the deposited clusters is large, they exist as large peninsular nuclei.The top of the island core has a strong shading effect on the concave part, that is the “shadow effect”.The projection of the surface is more conducive to capturing subsequent deposited atoms and preferential growth, resulting in an increasing degree of concavity on the surface to form conical or columnar crystals of sufficient size. Penetrating voids are formed between the conical crystals and the surface roughness value increases.Fine tissue can be obtained at high vacuum, with the decrease of vacuum degree, the microstructure of membrane becomes thicker and thicker.
Post time: May-24-2023