Lithography-free method yields durable antireflective glass

05 Jun 2024

AR performance achieved by nano-structured surface using thermally dewetted silver.

A team of scientists from research center ICFO and photonics materials manufacturer Corning has developed a new method for fabricating anti-reflective (AR) surfaces – achieved through nano-structured surfaces using a lithography-free process.

The method, described in ACS Applied Materials and Interfaces, utilizes thermally dewetted silver as an etching mask to create nanohole structures on glass surfaces, significantly reducing light reflection.

Anti-reflective (AR) surfaces are needed to minimize unwanted reflections, enhancing the efficiency of various optical devices such as laser optics, camera lenses, eyeglasses, touchscreen displays, and solar harvesting systems.

Avoiding complex lithography

In the new study, ICFO researchers Iliyan Karadzhov, Bruno Paulillo, and Juan Rombaut, led by ICREA Professor at ICFO Valerio Pruneri, in collaboration with Corning researchers Karl W. Koch and Prantik Mazumder, describe a simplified method that achieves nanostructured AR surfaces.

This approach uses thermally dewetted thin silver films as etching masks to generate subwavelength nanohole structures on the glass surfaces, characterized by its simplicity and cost-effectiveness by avoiding complex lithography. The results of this study have been recently published in the journal ACS Applied Materials and Interfaces.

The fabrication process involves three main steps. Initially, silver nanoparticles are obtained by quickly thermally annealing an ultra-thin silver film onto a glass substrate. These particles then serve as a base for a secondary etching mask, created by depositing a thin nickel layer over the silver nanoparticles and performing selective chemical wet etching. Finally, this mask is used in a dry etching process to carve nanoholes of varying depths into the glass surface.

The final arrangement and depth of the nanoholes are determined by the initial thickness of the silver film and the duration of the dry etch process. The team fabricated several samples with varying initial masks and hole depths, testing their performance by measuring both transmittance and reflectance in the visible and near-infrared ranges.

The newly developed AR surfaces exhibited a broadband omnidirectional response that achieves transmittance levels exceeding 99% in both the visible and near-infrared ranges, as well as maintaining high transmittance even at steep angles of incidence (up to 60 degrees).

The samples also demonstrated mechanical robustness and durability in abrasion tests. “One challenge was ensuring that the nanohole structures remained intact during abrasion tests while maintaining high optical performance,” said Karl W. Koch, a researcher at Corning Incorporated. “This was overcome by optimizing the nanoholes' geometry and the fabrication process to balance the mechanical and optical properties.”

Valerio Pruneri, the leading author of the study and NANO-GLASS project coordinator, concluded, “This new lithography-free method provides new possible solutions to the development of optoelectronic devices that require high transmission and durability.”