Abstract
Wavelength-selective coatings are broadly applied across diverse industries such as solar energy management, infrared sensing, telecommunications, laser optics, and eye-protective lenses. These coatings have historically not been optimized for hardness or mechanical durability and typically suffer from higher susceptibility to scratch and damage events than uncoated glass. In this work, we describe a family of wavelength-selective coatings with hardness and scratch resistance that are significantly higher than the chemically strengthened glass substrates on which the coatings are fabricated. The coatings are made using industrially scalable reactive sputtering methods. Wavelength-selective coatings are fabricated with nanoindentation hardness as high as 16–20 GPa over indentation depths ranging from 200 to 800 nm, as well as excellent durability in aggressive scratch testing. Tunable visible to near-infrared wavelength selectivity ratios (reflectance of stopband: reflectance of passband) as high as 7:1 are achieved. The feasibility of narrowband hard coating design is also demonstrated, with visible narrowband transmission having a peak FWHM of ~8 nm (~1.6%). A unique “buried layers” hard coating design strategy is shown to deliver particularly excellent hardness profiles. These designs can be tailored for a variety of different wavelengths and selectivity ratios, enabling new uses of wavelength-selective optics in mechanically demanding applications.
Highlights
Optical interference coatings utilize the physics of thin-film interference [1,2,3,4] to create unique optical properties that cannot be achieved using typical bulk materials
We show that, by expanding on the design principles of [16], we can create tunable wavelength-selective optical coatings that have very high levels of hardness and outstanding resistance to aggressive scratch testing
While hardness appears to be the dominating factor in the scratch resistance tests we have developed to mimic field scratches from the consumer electronics industry, modulus and H/E ratios may warrant further study for additional damage modes [29]
Summary
Optical interference coatings utilize the physics of thin-film interference [1,2,3,4] to create unique optical properties that cannot be achieved using typical bulk materials. These coatings have been studied and applied for a wide variety of uses, including low reflection optics [4,5], high reflection mirrors [6,7,8], solar energy management [9], telecommunications [10], infrared (IR) sensors [11,12] and more Despite this broad design flexibility and utility, optical interference coatings have historically suffered from relatively low scratch or damage resistance, especially when compared to modern chemically strengthened glasses, such as Corning Gorilla Glass®. We demonstrated a new optomechanical design approach, which dramatically boosted the hardness and practical scratch resistance of anti-reflection (AR) coatings [16] Versions of these high-hardness AR coatings have already been deployed on millions of consumer electronics devices with excellent manufacturing and field performance; these coatings have been shown to improve electronic display readability and enable reduced display energy consumption [17]. We demonstrate tunable broadband wavelength selectivity in the visible to near-infrared (NIR) wavelength range, as well as the feasibility of narrowband optical transmission
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