‘Previously Theorized’ – Researchers Demonstrate New Way to ‘Squeeze’ Infrared Light

Researchers have demonstrated that a specific class of oxide membranes can confine infrared light much more effectively than bulk crystals, which has promising implications for next-generation infrared imaging technologies. These thin-film membranes retain the desired infrared frequency while compressing the wavelengths, allowing greater image resolution. Using transition metal perovskite materials and advanced near-field synchrotron spectroscopy, the researchers showed that the phonon polaritons in these membranes can confine infrared light to only 10% of its wavelength. This discovery could lead to new applications in photonics, sensors and thermal management, with potential ease of integration into various devices. Credit: Yin Liu, NC State University

A new study reveals that oxide membranes can limit infrared light to a greater extent than traditional methods, promising advances in image resolution and applications in photonics and thermal management.

Researchers have successfully shown that a special type of oxide membrane can effectively limit or “squeeze” infrared light. This discovery could improve future infrared imaging technologies. These thin film membranes perform better than traditional bulk crystals in limited infrared light.

“The thin-film membranes retain the desired infrared frequency but compress the wavelengths, allowing imaging devices to capture higher-resolution images,” says Yin Liu, co-corresponding author of a paper on the work and an assistant professor of materials science and engineering in North Carolina State University.

“We have demonstrated that we can limit infrared light to 10% of its wavelength while maintaining its frequency – meaning that the amount of time it takes a wavelength to travel is the same, but the distance between the wave peaks is much closer together Bulk crystal techniques limit infrared light to about 97% of its wavelength.

Experimental Advances in Thin Film Technology

“This behavior was previously only theorized, but we were able to demonstrate it experimentally for the first time both through the way we prepared the thin-film membranes and our novel use of synchrotron near-field spectroscopy,” says Ruijuan Xu, co-director. author of the paper and an assistant professor of materials science and engineering at NC State.

For this work, the researchers worked with transition metal perovskite materials. Specifically, the researchers used pulsed laser deposition to grow a 100-nanometer-thick crystalline membrane of strontium titanate (SrTiO₃) in a vacuum chamber. The crystalline structure of this thin film is qualitative, which means that there are very few defects. These thin films were then removed from the substrate on which they were grown and deposited on the silicon oxide surface of a silicon substrate.

The researchers then used technology at Lawrence Berkeley National Laboratory’s Advanced Light Source to perform near-field synchrotron spectroscopy on the thin film of strontium titanate while exposed to infrared light. This enabled the researchers to capture the interaction of the material with infrared light in the nanoscale.

Understanding energy transfer: phonons, photons and polaritons

To understand what the researchers learned, we need to talk about phonons, photons, and polaritons. Phonons and photons are both ways that energy travels through and between materials. Phonons are essentially waves of energy caused by the way atoms vibrate. Photons are essentially waves of electromagnetic energy. You can think of phonons as units of sound energy, while photons are units of light energy. Phonon polaritons are quasi-particles that occur when an infrared the photo it is coupled to an “optical” phonon – meaning a phonon that can emit or absorb light.

“Theoretical papers proposed the idea that transition metal perovskite oxide membranes would allow phonon polaritons to confine infrared light,” says Liu. “And our work now shows that the phonon polaritons confine the photons and also prevent the photons from extending beyond the surface of the material.

“This work creates a new class of optical materials for controlling light at infrared wavelengths, which has potential applications in photonics, sensors and thermal management,” says Liu. “Imagine being able to design computer chips that could use these materials to shed heat by converting it to infrared light.”

“The work is also exciting because the technique we have demonstrated for creating these materials means that thin films can be easily integrated with a wide variety of substrates,” says Xu. “This should make it easy to incorporate the materials into many different types of devices.”

Reference: “Highly confined-near-zero and surface epsilon phonon polaritons in SrTiO3 membranes” by Ruijuan Xu, Iris Crassee, Hans A. Bechtel, Yixi Zhou, Adrien Bercher, Lukas Korosec, Carl Willem Rischau, Jérésierite, Tevin. , Yonghun Lee, Stephanie N. Gilbert Corder, Jiarui Li, Jennifer A. Dionne, Harold Y. Hwang, Alexey B. Kuzmenko, and Yin Liu, 4 Jun 2024, Nature Communications.
DOI: 10.1038/s41467-024-47917-x

The research was done with the support of the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering, under contract no. DE-AC02-76SF00515; and by the National Science Foundation under grant number 2340751.