The principle of vacuum tube coating in vacuum coating machines is that electrons, accelerated towards the substrate under the influence of an electric field, collide with argon atoms, ionizing into a large number of argon ions and electrons. The electrons then fly towards the substrate. Argon ions, accelerated by the electric field, bombard the target material, sputtering out a large number of target atoms, which, as neutral target atoms (or molecules), deposit onto the substrate to form a film. Secondary electrons, during their acceleration towards the substrate, are influenced by the Lorentz force of the magnetic field and are confined to a plasma region near the target surface. This region has a high plasma density, and the secondary electrons, under the influence of the magnetic field, move in a circular motion around the target surface.
This long path of motion involves continuous collisions with argon atoms, ionizing into a large number of argon ions that bombard the target material. After multiple collisions, the electrons gradually lose energy, break free from the magnetic field lines, move away from the target material, and finally deposit onto the substrate. Now, with the addition of a medium-frequency magnetron sputtering target, the evaporating molecules of the film are accelerated and bombarded by the target material under the action of an electric field, sputtering out a large number of target atoms.
The neutral target atoms (or molecules) are deposited on the substrate to form a film, which solves the problem of film types that could not be processed by natural evaporation in the past, such as titanium plating, zirconium plating, etc.
Currently, aluminum-nitrogen composite film are commonly used in vacuum tubes. The entire film consists of three layers: inner, middle, and outer, each with its own function. The inner layer is a reflective layer, whose main function is to prevent the heat from the hot water in the tube from radiating outwards.
The middle layer is an absorption layer, whose main function is to absorb light energy and convert it into heat energy.
The outer layer is an anti-reflective layer, whose main function is to reduce the reflection of sunlight and increase the absorption rate of sunlight.
