There are three basic methods to deposition of nano-coatings by PVD: vacuum evaporation, vacuum sputtering, and vacuum ion plating. Vacuum evaporation refers to using electron beam heating, laser heating and other methods to make evaporation source material evaporated into particles (atoms or ions), and then deposit on the surface as coating. The coating has relatively more pores, and the substrate adhesion is not very good. The sputtering coating uses the workpiece as the anode and the target as the cathode. The argon ions generated by argon ionization are used to sputter the target atoms and then deposit it on the surface of the workpiece. The coating has fewer pores and better adhesion to the substrate. Ion plating means using evaporation, sputtering or chemical methods to make the material turn into atoms and be ionized by the plasma around the substrate. And then, these ionized atoms flew to the substrate with greater kinetic energy under the action of the electric field to form a coating. This coating is uniform and dense with good adhesion, basically non-porous.
Gutarra successfully made titanium oxide nano-films by using DC magnetron sputtering technology. The pressure in the sputtering chamber was evacuated to 1.3×10-4 Pa, and then after charging Ar, O2 and CF4, the total pressure was 1.3 Pa (control their injection volume during sputtering). The thickness of the film was controlled by varying the sputtering conditions at a constant sputtering voltage (700 V), the substrate temperature was controlled at 100 ~ 400°C during sputtering process. However, the coating surface is impacted by gas and charged particles, and the performance of the coating is greatly affected by the plasma state. Besides, the sputtering conditions are not easily controlled, which is the biggest weakness of this method.
In order to further improve the quality of nano-coatings, various advanced PVD technologies have been combined to develop and derive various advanced PVD technologies. The magnetic field is introduced into the sputtering technique that mainly uses the electric field, and then various magnetron sputtering techniques have been developed. In order to enhance the chemical processes in the formation of thin films, active reaction gases are introduced into coating process of evaporation, sputtering, and ion plating to form active reaction vaporization techniques, active reaction sputtering techniques, and active reaction ion plating techniques. In addition, there are more new coating technologies such as pulsed laser deposition (PLD), magnetron sputtering pulsed laser deposition (MSPLD), and ionized magnetron sputtering, molecular beam epitaxy (MBE) and so on.
It is observed that with the development of science and technology, the boundaries between CVD and PVD are more and more blurred, and they penetrate each other, thus these two coating technologies will be more perfect.