Antireflection coatings with sapphire-like hardness are highly desired in advanced engineering applications. Currently, classic (LH)^n structures based on Si3N4/SiO2 stacks are widely used to obtain high optical transparency and surface hardness in industry. However, it still suffers from low durability and multiple failures after wear and scratch tests. Herein, we selected Ta2O5/Si3N4 nanolaminates to fabricate toughened AR coatings with similar refractive indices, overcoming the brittleness of thick nitride films. Furthermore, we proposed another graded AR coating, using a“Step up-step down" method to combine the hardness gradient structure with optical design. The toughened AR coating exhibited a low reflectance of 0.8% (420-780 nm) and a remarkable hardness of 22.8 GPa, meanwhile demonstrating the ability to withstand abrasion from steel wool up to 3,000 times. The graded AR coating achieves high transparency (Tave>98.8%, 420-720 nm), high surface hardness (H>23 GPa), and low residual stress (~680 MPa). Notably, no additional damage was observed during 6 months after the scratch test, such as cracking, peeling, and delamination.
Here we propose a novel broadband absorber with high efficiency by depositing nanometer iridium (Ir) film onto porous anodic alumina (PAA) template so as to increase the optical path length of the incident light for its great absorption property. Distinguished from the narrow band absorber using sub-wavelength resonant dielectric nanostructures and excitation of the propagating surface plasmon (PSP), PAA with nanometer Ir film can present broadband absorption with high efficiency as a result of the superposition of many different plasmon-enhanced absorption peaks by utilizing light funneling. The average absorption is able to achieve as high as 93.4% for 400-1100nm wavelength band and 96.8% for improved structure of quadrangular frustum pyramid array. And not only the hexagonal latticed structures of PAA template but also many similar structures based on grating or holes with square latticed or other latticed mode are able to achieve the broadband absorption with high efficiency. The absorption caused by the Ir metal layer deposited on the bottom of PAA and the funneled light into the alumina absorbed within the Ir film covering the inner sidewalls, both contribute the broadband absorption of the proposed absorber. This novel absorber can be implemented in fields of solar cell, light harvesting, imaging and so forth.
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