Invisible Glass

Brookhaven National Laboratory’s Center for Functional Nanomaterials (CFN) has developed a method for creating surface nanotextures that effectively eliminates optical reflections from glass, silicon, and plastics.

Invisible Glass

The nanotextured glass is antireflective over the entire visible and near-infrared spectrum and across a wide range of viewing angles. Even at viewing angles as high as 70°, more than 90% of light passes through the nanostructured glass, compared to 74% from untextured glass.

Unlike conventional thin-film antireflective coatings, this effect is not achieved by coating the glass with layers of different materials (typically polymers). Instead, the geometry of the surface itself is changed at the nanoscale. Because the final structure is composed entirely of glass, it is highly durable, withstanding three times more optical energy per unit area than commercial broadband antireflective coatings. In addition to increasing light transmission, these glass surfaces can withstand cleaning products containing alcohol or other solvents that typically cannot be used on antireflective coatings made with layered polymers.

This method leverages the patterning-forming abilities of thin films of block copolymers — an important class of industrial polymers used to manufacture many products, including shoe soles, adhesive tapes, and automotive interiors. Here, the block copolymers provide a physical template for plasma etching the glass surface into an array of nanometer (nm)-scale cone-shaped textures with sharp tips.

The nanotextures eliminate the abrupt change in refractive index at the air-material interface, minimizing optical reflections. Glass surfaces covered with 300-nm-tall cones reflect less than 0.2% of incoming red-colored light (633-nm wavelength), compared to 4% from untreated glass. When this technique is applied to both sides of a glass window, more than 99.7% of incident visible light is transmitted — making the glass essentially invisible.

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