Physical Vapor Deposition (PVD)
Introduction
Physical vapor deposition (PVD) refers to the physical method of evaporating the surface of the material source into gaseous atoms or molecules under vacuum conditions, and depositing films with special functions on the substrate surface through low-pressure gas transport. According to the coating requirements, different types of PVD processes can be used, such as: cathodic arc deposition (Arc-PVD), electron beam PVD (EBPVD), evaporation deposition, sputtering deposition, ion plating, etc. The most common PVD technologies include vacuum evaporation, vacuum sputtering and ion plating.
Vacuum Evaporation
Vacuum evaporation means that the material source is heated by the evaporator to sublimate under vacuum conditions and the evaporated particle stream directly shoots at the substrate and condenses on the substrate to form a film. Materials of evaporation source include but are not limited to metal, inorganic substrate, organic substrate, etc. For example, using hexathiophene as the evaporation source, , hexathiophene films with orderly molecules can be deposited on the flexible polyvinyl pyrrolidone (PVP) insulation layer and the flexible indium tin oxide (ITO) transparent conductive layer by vacuum evaporation by controlling the substrate temperature and growth rate. Polyaniline and its derivative films can also be prepared as evaporation sources.
Vacuum Sputtering
Sputtering means that the material source (called target) and the substrate are put into the vacuum chamber together, and then the positive ions are used to bombard the target as the cathode, so that the atoms and molecules in the target escape and condense on the substrate surface to form a film. Sputtered coatings can be divided into direct-current (DC) sputtering, radio frequency (RF) sputtering and magnetron sputtering. The corresponding glow discharge voltage source and control field are high voltage DC, RF alternating current and magnetron fields, respectively. Sputtering targets are usually metal or inorganic compounds. Single metal target is usually sputtered with DC power, while metal compound or inorganic compound is sputtered with RF power.
Ion Plating
Ion plating changes and controls the composition and properties of the deposited film by simultaneously or periodically bombarding the deposited film with atomic-sized high-energy particles. Ion plating can produce solid lubricating film with good lubricating performance. For example, the solid lubricating films TiN-MoS2/Ti and TiN-MoS2/WSe2 are typical multiphase nanocomposite films, in which MoS2 is basically quasi amorphous, and doped Ti or WSe2 is multiphase compounded with MoS2 to form multiphase nanocomposite films. The properties of these films are characterized by low friction coefficient, low friction noise, high moisture oxidation resistance, good high and low temperature performance, strong dust wear resistance and long wear life.
Application
With the improvement of deposition methods and technologies, PVD can deposit not only metal films, alloy films, but also compounds, ceramics, semiconductors, polymer films, etc. PVD had some applications as early as the beginning of the 20th century, but in recent years, it has rapidly developed into a new technology with broad application prospects, and is gradually developing towards environment-friendly and clean. For example, in the clock industry, especially in the surface treatment of high-grade watch metal appearance parts, it has become more and more widely used. In addition, PVD has been widely used in mold production, building decoration, electricity, medicine and other fields. With the further optimization of auxiliary equipment, materials and processes, as well as the common progress with other cross disciplines, the application prospect of PVD technology will be more broad.
Reference
- Mattox, Donald M. Physical vapor deposition (PVD) processes. Metal Finishing, 2002, 100: 394-408.