A thin film is a thin coating layer used in a variety of technologies. Although they are widely used, much of their research is focused on how they act as a barrier to various stimuli, or as a conductor. Our next topic of discussion is optical thin films, which we will discuss next.
Thin optical films are thin, transparent layers of materials used to enhance transmission, reflection, and/or polarization characteristics of optical components. An optical part can be fabricated on a simple substrate such as a glass lens or on a more complicated one such as an optical component.
A coating’s thickness and atomic composition vary from coating to coating, since the thickness has a large impact on how the optical film behaves, with a particular emphasis on how different thicknesses can be tuned to work with particular wavelengths of light. Even though the coating thickness will differ from application to application, it must be at least 500 nm thick to be effective against all wavelengths of visible light. Optical components can also be coated with anti-reflective thin film coatings in this class. For more information, visit alluxa.com.
It is very rare for a surface to exhibit a perfect optical property on its own, so optical thin films are applied to the surface of optical components. Most optical components in use today have been coated with some sort of thin film to enhance their properties. Coatings are applied to the outside surface of optical components, so they are often intended to improve not only the optical properties of the surface but also the corrosion resistance.
Thin optical films are usually composed of multiple atomic layers, which makes them more complicated than other types of coatings. In general, these layers consist of a combination of metallic and dielectric layers, whose thickness varies according to the coating’s intended properties. Differences in refractive index between layers, surfaces and air in between all affect the way light reflects, refracts, and transmits into an optical component at the nanoscale.
Optical effects are achieved by layering up to hundreds of layers of thin film coatings, and the process of determining the ideal size and composition of each layer can involve complex calculations performed by a computer. Over the years, computational capabilities have increased, which has resulted in more complex and effective optical coatings.
It is not all that different from fabricating other thin films or creating ultra-thin nanomaterials to create optical thin films. Deposition techniques are the primary way to create optical thin films.
Most commonly, PVD is used to generate layers of films, which may include evaporative deposition, plasma sputtering, and ion beam sputtering.
Atomic layer deposition is another technique outside of PVD that is used to create these films. It is technically a type of chemical vapor deposition (CVD). While fabricating these films is not the simplest task, atomically precise thin films are essential for providing the benefits and that is the main reason why these methods are used.
Many factors influence the choice of fabrication method, including the time taken for a coating to be deposited, the geometry of the surface, the coating stress, and the coating performance.