Optical properties of vacuum silvered thin films

Optical properties of vacuum silvered thin films

Optical thin films are realized in a high-vacuum coating chamber. Conventional coating processes require elevated substrate temperatures (typically around 300°C); more advanced techniques, such as ion-assisted deposition (IAD), can be performed at room temperature. The IAD process not only produces films with better physical properties than conventional coating processes, but can also be applied to substrates made of plastic. The traditional method of thin film deposition has been thermal evaporation, either with resistively heated evaporation sources or with electron beam evaporation sources. The film properties are mainly determined by the energy of the deposited atoms, which are only about 0.1 eV in conventional evaporation. IAD deposition results in direct deposition of ionized vapor and adds activation energy to the growing film, typically on the order of 50 eV. The ion source improves the film properties of conventional electron beam evaporation by directing the beam from the ion gun to the substrate surface and the growing film.

The optical properties of thin films, such as refractive index, absorption and laser damage threshold, mainly depend on the microstructure of the film layer. Film material, residual gas pressure, and substrate temperature can all affect the microstructure of the film. If the evaporatively deposited atoms have low mobility on the substrate surface, the film will contain micropores. When the film is exposed to moist air, these pores are gradually filled with water vapor.

The combination of vacuum silver-plated substrate and film layer.

In general, in anti-reflection films, this is the main reason for the weakness of the film. Since the surface of the substrate will inevitably have some harmful impurities attached to the surface during the optical cold working and cleaning process, and the surface of the substrate will always have some damage layers due to the effect of optical cold working, and impurities (such as water vapor) that penetrate into the damage layer , oil vapor, cleaning liquid, wiping liquid, polishing powder, etc., of which water vapor is the main one), it is difficult to remove it by ordinary methods, especially for substrates with good hydrophilicity and strong adsorption. When the film material molecules accumulate on these impurities, it affects the adhesion of the film layer, which also affects the film strength.

In addition, if the hydrophilicity of the substrate is poor and the adsorption force is poor, the adsorption to the film layer is also poor, which will also affect the film strength.

The chemical stability of the nitrate material is poor, and the surface of the substrate has been corroded during the circulation process in the pre-processing process, forming a corrosion layer or a hydrolysis layer (perhaps localized and extremely thin). When the film is plated on the corrosion layer or the hydrolysis layer, its adsorption is poor, and the film firmness is poor.

The surface of the substrate has dirt, oil spots, gray spots, drool spots, etc., and the local film layer is poorly adhered, resulting in poor local film firmness.

www.superbheater.com