Method fabricates nanostructures with angle-independent structural color

Nanostructures that interact with light to produce structural color have a variety of applications in photonics, photovoltaics, photocatalysis, sensing and beyond. However, mass producing nanostructures with visible-wavelength structural color is often difficult, limiting their fabrication to the small scale and certain substrates.

Shapturenka et al. developed a scalable fabrication method to produce visible-wavelength nanostructures on any substrate. The authors combined standard nanofabrication techniques with an area-scalable nanosphere coating technique, known as Langmuir-Blodgett deposition, to create thin, partially suspended hole arrays of titanium dioxide (TiO₂) on silicon. The arrays are quasi-ordered, meaning their holes are arranged in an imperfect honeycomb-like pattern that the close-packed nanosphere monolayers naturally form.

Importantly, hole arrays made with this combination method exhibit vivid, angle-independent structural color that can be tuned across the visible-light spectrum by changing the hole spacing and processing. Optical simulations showed the hole array supports in-plane optical modes that filter out optical cavity modes in the highly porous underlayer, resulting in the angle-independent optical behavior.

The structural color of these nanostructures could be used for fade-resistant coloration, because their operation does not involve pigments or chromophores. The wide acceptance angle could also be used to improve light harvesting of solar cells and enhance the efficiency of filters, sensors and solid-state light emitters.

“To our knowledge, this is a novel contribution to the structural-color toolkit available in nature and prior work,” said author Pavel Shapturenka. The authors are currently working on incorporating these nanostructures into miniature optical sensors and light-emitting devices.

Source: “Quasi-ordered, sub-wavelength TiO₂ hole arrays with tunable, omnidirectional color response,” by Pavel Shapturenka, Fabian Birkholz, Nicholas Isaac Zakaria, Steven P. DenBaars, and Michael J. Gordon, JVST: A (2020). The article can be accessed at https://doi.org/10.1116/6.0000328 .