Thin film membranes confine infrared light

In a boost for next generation imaging technologies, researchers have shown for the first time that a specific class of oxide membranes can confine infrared light.

The researchers worked with transition metal perovskite materials
The researchers worked with transition metal perovskite materials - Yin Liu, NC State University

The thin-film membranes are said to confine infrared light far better than bulk crystals, which are the established technology for infrared light confinement.

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

“We’ve demonstrated that we can confine infrared light to 10 per cent of its wavelength while maintaining its frequency – meaning that the amount of time that it takes for a wavelength to cycle is the same, but the distance between the peaks of the wave is much closer together. Bulk crystal techniques confine infrared light to around 97 per cent of its wavelength.”

“This behaviour was previously only theorised, but we were able to demonstrate it experimentally for the first time through both the way we prepared the thin-film membranes and our novel use of synchrotron near-field spectroscopy,” said Ruijuan Xu, co-lead 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. The researchers used pulsed laser deposition to grow a 100nm thick crystalline membrane of strontium titanate (SrTiO3) in a vacuum chamber. The crystalline structure of this thin film is high quality with very few defects. These thin films were then removed from the substrate and placed on the silicon oxide surface of a silicon substrate.

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

“Theoretical papers proposed the idea that transition metal perovskite oxide membranes would allow phonon polaritons to confine infrared light,” Liu said in a statement. “And our work now demonstrates that the phonon polaritons do confine the photons, and also keep the photons from extending beyond the surface of the material.

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

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

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