Adhesion and mechanical properties of anti-reflective coatings
This application report demonstrates the use of nano-scratch and instrumented nanoindentation testing to characterize the adhesion and mechanical properties of anti-reflective coatings.
An anti-reflective (AR) coating is a specialized layer applied to glass and glass-like substrates, such as sapphire, to minimize reflections and enhance light transmission, thereby improving overall optical clarity. These coatings are typically composed of high-refractive-index materials, such as titanium dioxide (TiO2) or silicon dioxide (SiO2), which are selected for their ability to significantly reduce light reflection at the glass-air interface. The typical thickness of AR layers is around 120 nm, which is related to one quarter of the wavelength of the most abundant green light (550 nm). By effectively altering the refractive properties of the glass, AR coatings decrease glare and reflections, leading to clearer vision and better image quality. This enhancement is particularly beneficial in various applications, including ophthalmic lenses, camera optics, display screens, and watch crystals. In addition to these functional benefits, anti-reflective coatings also contribute to a more aesthetically pleasing appearance by reducing undesired surface reflections. However, to maintain their optical functionality, these coatings must adhere well to the glass substrate. Therefore, characterizing their adhesion and mechanical properties is crucial and must be accurately determined.
This application report demonstrates how Anton Paar nano scratch tester (NST3) and ultra nanoindentation tester (UNHT3) are used to measure such mechanical properties.
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