New Thin-Film Membranes Revolutionize Infrared Imaging

Researchers from North Carolina State University discovered that a specific class of oxide membranes can confine, or “squeeze,” infrared light. This finding has significant implications for the development of next-generation infrared imaging technologies. The study was published in the open-access journal Nature Communications.

New Thin-Film Membranes Revolutionize Infrared Imaging

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Thin-film membranes confine infrared light much 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.

Yin Liu, Study Co-Corresponding Author and Assistant Professor, Department of Materials Science and Engineering, North Carolina State University

Yin Liu adds, “We’ve demonstrated that we can confine infrared light to 10% 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% of its wavelength.”

This behavior was previously only theorized, 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.

Ruijuan Xu, Study Co-Lead Author and Assistant Professor, Department of Materials Science and Engineering, North Carolina State University

For this investigation, the researchers used transition metal perovskite materials. They utilized pulsed laser deposition to grow a 100 nm thick crystalline membrane of strontium titanate (SrTiO3) within a vacuum chamber. This thin film has very few defects due to its high-quality crystalline structure. After that, the thin films were placed on a silicon substrate’s silicon oxide surface and separated from the substrate they had grown on.

Subsequently, the strontium titanate thin film was exposed to infrared light, and the researchers used synchrotron near-field spectroscopy at the Advanced Light Source of Lawrence Berkeley National Laboratory. This made it possible for the researchers to record the material’s nanoscale interaction with infrared light.

To fully appreciate the findings of the researchers, we need to delve into phonons, photons, and polaritons. Both phonons and photons are carriers of energy through and across materials.

Phonons are waves generated by the vibrations of atoms, essentially representing sound energy. Photons, in contrast, are electromagnetic waves, representing light energy. Phonon polaritons are hybrid quasi-particles that emerge when an infrared photon interacts with an 'optical' phonon—a type of 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. 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.

Yin Liu, Study Co-Corresponding Author and Assistant Professor, Department of Materials Science and Engineering, North Carolina State University

Liu said, “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. Imagine being able to design computer chips that could use these materials to shed heat by converting it into infrared light.”

Xu said, “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. That should make it easy to incorporate the materials into many different types of devices.”

The study was co-authored by a team from several renowned institutions. Iris Crassee and Alexey Kuzmenko from the University of Geneva served as the co-lead and co-corresponding authors, respectively. Their colleagues from the University of Geneva, Yixi Zhou, Adrien Bercher, Lukas Korosec, Carl Willem Rischau, and Jérémie Teyssier; Hans Bechtel and Stephanie Gilbert Corder from the Lawrence Berkeley National Laboratory; Kevin Crust, Yonghun Lee, Jiarui Li, and Harold Hwang from Stanford University and the SLAC National Accelerator Laboratory; and Jennifer Dionne also from Stanford University, contributed as co-authors.

The project received funding from the National Science Foundation and the US Department of Energy’s Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Journal Reference:

Xu, R., et al. (2024) Highly confined epsilon-near-zero and surface phonon polaritons in SrTiO3 membranes. Nature Communications.

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