Rice ‘metallenes’ could disrupt vacuum UV market

HOUSTON – (May 5, 2022) – Photonics researchers at Rice University have created potentially disruptive technology for the ultraviolet optics market.

By precisely etching hundreds of tiny triangles on the surface of a microscopic film of zinc oxide, the pioneer of nanophotonics Naomi Hallas and his colleagues have created a “metalene” that transforms incoming long-wave UV (UV-A) into a focused output of Vacuum UV radiation (VUV). VUV is used in semiconductor manufacturing, photochemistry and materials science and has historically been expensive to use, in part because it is absorbed by nearly all types of glass used to make conventional lenses.

“This work is particularly promising in light of recent demonstrations that chipmakers can scale up the production of metasurfaces with CMOS-capable process,” said Halas, corresponding co-author of a metalens demonstration study Posted in Scientists progress. “This is a fundamental study, but it clearly points to a new strategy for high-throughput manufacturing of compact VUV optical components and devices.”

The Halas team showed that their microscopic metalenes could convert 394 nanometer UV into a focused 197 nanometer VUV output. The disc-shaped metal is a transparent sheet of zinc oxide thinner than a sheet of paper and barely 45 millionths of a meter in diameter. During the demonstration, a 394-nanometer UV-A laser was shot through the back of the disk, and the researchers measured the light emerging from the other side.

Co-first author of the study Catherine Arndtgraduate student in applied physics at Halas research groupsaid the main feature of metalene is its interface, a front surface dotted with concentric circles of tiny triangles.

“The interface is where all the physics takes place,” she said. “We are actually imparting a phase shift, changing both the speed at which light travels and the direction in which it travels. We don’t have to collect the luminous flux because we use electrodynamics to redirect it to the interface where we generate it. »

Violet light has the lowest wavelength visible to humans. Ultraviolet has even lower wavelengths, which range from 400 nanometers to 10 nanometers. Vacuum UV, with wavelengths between 100 and 200 nanometers, is so named because it is strongly absorbed by oxygen. Using VUV light today typically requires a vacuum chamber or other specialized environment, as well as machinery to generate and focus the VUVs.

“Conventional materials generally don’t generate VUVs,” Arndt said. “It’s done today with nonlinear crystals, which are bulky, expensive and whose exports are often controlled. The result is that the VUV is quite expensive.

In previous workHalas, rice physicist Pierre Nordlander, former rice Ph.D. student Michael Semlinger and others have demonstrated that they can transform 394 nanometer UV to 197 nanometer VUV with a zinc oxide metasurface. Like the metalens, the metasurface was a transparent film of zinc oxide with a patterned surface. But the required pattern wasn’t as complex because it didn’t need to focus the light output, Arndt said.

“Metalenses takes advantage of the fact that the properties of light change when it hits a surface,” she said. “For example, light travels faster in air than in water. This is why you get reflections on the surface of a pond. The water surface is the interface, and when sunlight hits the interface, a small part is reflected.

Previous work has shown that a metasurface can produce VUVs by converting long-wave UVs through a frequency-doubling process called second harmonic generation. But the VUV is expensive, in part because it’s expensive to handle after it’s produced. Commercially available systems for this can fill cabinets as large as refrigerators or compact cars and cost tens of thousands of dollars, she said.

“For a metalens, you’re trying to both generate light and manipulate it,” Arndt said. “In the domain of visible wavelengths, metalens technology has become very efficient. Virtual reality headsets use it. Metalenses have also been demonstrated in recent years for visible and infrared wavelengths, but no one had done so at shorter wavelengths. And many materials absorb VUVs. So for us, it was just an overall challenge to see, ‘Can we do this?’

To make the metalens, Arndt worked with co-corresponding author Din Ping Tsai from the City University of Hong Kong, which helped produce the complex metalens surface, and with three co-first authors: Semmlinger, a 2020 Rice graduate, Zhang Minggraduated from Rice in 2021, and Ming Lun TsengAssistant Professor at National Yang Ming Chiao Tung University in Taiwan.

Tests at Rice showed that the metalens could focus their 197-nanometer output into a spot measuring 1.7 microns in diameter, increasing the power density of the light output by 21 times.

Arndt said it’s too early to tell if the technology can compete with state-of-the-art VUV systems.

“It’s really fundamental at this point,” she said. “But he has a lot of potential. It could be made much more efficient. With this first study, the question was: “Does it work?” In the next phase, we will ask ourselves: “How much can we improve it?” »

Halas holds the Stanley C. Moore Professorship in Electrical and Computer Engineering from Rice, director of Rice’s Smalley Curl Institute and Professor of Chemistry, Bioengineering, Physics and Astronomy, Materials Science, and Nanoengineering. Nordlander, co-author of the study, is a Wiess professor and professor of physics and astronomy, and a professor of electrical and computer engineering, materials science and nanoengineering.

Additional study co-authors include Benjamin Cerjan and Rice’s Jian Yang; Tzu-Ting Huang and Cheng Hung Chu from Academia Sinica in Taiwan; Hsin Yu Kuo of National Taiwan University; Vin-Cent Su of United National Taiwan University; and Mu Ku Chen from City University of Hong Kong.

The research was funded by the Ministry of Science and Technology of Taiwan (107-2311-B-002-022-MY3, 108-2221-E-002-168-MY4, 110-2636-M-A49-001 ), National Taiwan University (107-L7728, 107-L7807, YIH-08HZT49001), Shenzhen Science and Technology Innovation Commission (SGDX2019081623281169), University Grants Committee/Research Grants Council of Administrative Region Hong Kong Special Committee in China (AoE/P-502/20), Department of Science and Technology of Guangdong Province of China (2020B1515120073), Department of Electrical Engineering, City University of Hong Kong (9380131) , Taiwan Ministry of Education Yushan Young Scholar Program, Taiwan Academia Sinica Applied Science Research Center, Robert A. Welch Foundation (C-1220, C-1222), National Science Foundation (1610229, 1842494), Air Force Office of Scientific Research (MURI FA9550-15-1-0022) and Defense Thre at Reduction Agency ( HDTRA1-16-1-0042).

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Peer-reviewed study:

“Vacuum Ultraviolet Nonlinear Materials”, Scientists progress
https://doi.org/10.1126/sciadv.abn5644

Image downloads:

https://news-network.rice.edu/news/files/2022/05/0509_METALENS-ca37-lg.jpg
CAPTION: Rice University graduate student Catherine Arndt helped create potentially disruptive technology for ultraviolet optics, a solid-state “metalene” that transforms long-wave UV into “vacuum UV” radiation “Focused. (Photo by Jeff Fitlow/Rice University)

https://news-network.rice.edu/news/files/2022/05/0509_METALENS-Fig-lg.jpg
CAPTION: By precisely etching hundreds of tiny triangular nanoresonators in precisely configured concentric circles onto a microscopic film of zinc oxide, photonics researchers at Rice University have created a “metalene”, a semi-transparent device -conductors thinner than a sheet of paper that bends light. like a classic lens. Rice’s metalene converts 394 nanometer ultraviolet light (blue) to 197 nanometer “vacuum UV” (pink) and simultaneously focuses the VUV output onto a small spot less than 2 millionths of a meter in diameter. (Infographic by M. Semmlinger/Rice University)

https://news-network.rice.edu/news/files/2022/05/0509_METALENS-ca52-lg.jpg
CAPTION: Catherine Arndt is a graduate student in applied physics at Rice University. (Photo by Jeff Fitlow/Rice University)

https://news-network.rice.edu/news/files/2022/05/0509_METALENS-nh30-lg.jpeg
CAPTION: Naomi Halas of Rice University is an engineer, chemist and pioneer in the field of light-activated nanomaterials. (Photo by Jeff Fitlow/Rice University)

This press release is available online at news.rice.edu.

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