Initial knowledge of vacuum evaporation coating process
The main components of vacuum evaporation equipment structure are as follows:
(1) vacuum chamber, which provides necessary vacuum degree for evaporation and prevents materials from being oxidized during evaporation; (2) evaporating source and evaporating heater, which are mainly used to place evaporating materials and heat them; (3) substrate for receiving evaporating substances and forming a solid evaporating film on its surface; (4) base plate heater, used for heating the base plate; (5) temperature measuring device is a thermocouple temperature measuring device.
Vacuum evaporation coating consists of the following processes. 1. Heating and evaporation process, including the phase transition from condensed phase to gas phase (solid phase, liquid phase or gas phase). When a compound is vaporized from each substance at a different temperature and at a different saturation vapor pressure, its components react with each other, some of which enter the evaporation space as gaseous or vapor.2. Transport of vaporized atoms or molecules between evaporation source and substrate. The number of collisions between these particles and the residual gas molecules in the vacuum chamber during the flight of space depends on the number of collisions between the gas molecules of the evaporated atoms, the average free path of the evaporated atoms, and the distance between the evaporated source and the substrate. 3. The process by which vaporized atoms or molecules are deposited on the substrate, that is, the process of vapor condensation, nucleation, nuclear growth and the formation of continuous thin films. Since the substrate temperature is much lower than that of the evaporation source, the phase transition of the sediment molecules directly occurs on the substrate surface from the gas phase to the solid phase.
In the process of vacuum evaporation, vacuum environment for evaporation coating has a decisive role, because of evaporation of atoms or molecules will collide with the large number of air molecules, pollution of the membrane layer, forming oxide or even evaporation source is heated oxidation burning, or due to the collision block air molecules, difficult to form homogeneous continuous thin film. So it's important to have a stable vacuum, and the evaporation process also involves the saturation vapor pressure theory of the material. So you also need to know something about the saturation vapor pressure to understand the evaporation process.
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