Ion Assisted Deposition (IAD)
IAD utilizes the evaporative method described previously, but adds a high energy ion beam that is directed at the part to be coated. These ions impart energy to the deposited material – acting almost like an atomic sized hammer – resulting in a higher film density than achieved with purely evaporative methods. The ion beam can also be used to pre-clean or etch the surface of the substrate, which can improve film adhesion. The combination of a relatively cold deposition process and the ion pre-clean affords the opportunity to coat plastic substrates such as polycarbonate lenses or visors, and even enables deposition on the ends of jacketed fibers and the top of photo-resist masks.
The higher density of IAD coatings generally gives them more mechanical durability, greater environmental stability and lower scatter than evaporative films. Furthermore, the amount of energetic assistance can be varied from zero to a maximum level on a layer by layer basis, giving the process tremendous flexibility. For example, while IAD is not compatible with some of the commonly used materials in the infrared, it can be used solely on the outermost layer to yield an overall coating with superior durability. The ion energy can also be used to modify the intrinsic stress of a film during deposition. In some cases, this can change the film stress from tensile to compressive. This can help to maintain substrate surface figure, especially when depositing thick infrared coatings.
Click the image below to VIEW IAD Coating Model