KAIST Overcomes Resolution Limit of X-ray Microscopy

Domestic researchers have developed an X-ray microscope capable of precisely examining the internal structures of semiconductors and batteries.

The Korea Advanced Institute of Science and Technology (KAIST) announced on the 12th that Professor Yong-Geun Park's research team from the Department of Physics, in collaboration with Dr. Im Jun's research team from the Pohang Accelerator Laboratory, successfully developed a core technology that overcomes the resolution limits of existing X-ray microscopes.

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X-ray microscopes have the advantage of penetrating most materials, allowing non-invasive observation of internal organs and skeletons through chest X-rays or CT scans. Recently, active research has been conducted to enhance the resolution of X-ray imaging technology to precisely observe the internal structures of semiconductors and batteries at the nanoscale.

X-ray nano microscopes do not use refractive lenses; instead, they employ circular gratings called zone plates as lens substitutes. The resolution of images obtained using zone plates is determined by the fabrication quality of the zone plate's nanostructures. Producing and maintaining these nanostructures presents various challenges, and these limitations have defined the resolution limits of X-ray microscopes.

To overcome this issue, the research team developed a new X-ray nano microscope technology. The X-ray lens proposed by the team consists of a thin tungsten film perforated with numerous holes. It diffracts the incident X-rays to generate random diffraction patterns. Paradoxically, the team mathematically demonstrated that high-resolution information of the sample is fully contained within these random diffraction patterns, and they successfully extracted and visualized the sample information.

This imaging technique, which utilizes the mathematical properties of random diffraction, was first proposed and implemented in the visible light spectrum in 2016 by Dr. Gyore Lee and Professor Yong-Geun Park, and was published in Nature Communications at that time. The current research applies these prior findings to solve challenges in the X-ray domain.

The resolution of the constructed sample images does not directly correlate with the size of the etched patterns on the random lens used. Based on this idea, the team used a random lens fabricated with circular patterns of 300 nanometers (nm) in diameter to successfully acquire images with a resolution of 14 nm (approximately one-seventh the size of the coronavirus). The imaging technology developed by the team is a key foundational technology that can elevate the resolution of X-ray nano microscopes beyond the limits imposed by the fabrication challenges of conventional zone plates.

Gyore Lee, the first author and co-corresponding author and a physicist at KAIST, stated, “By utilizing next-generation X-ray sources and high-performance X-ray detectors, we expect to surpass the resolution of existing X-ray nano imaging and approach around 1 nm, which is the resolution level of electron microscopes.” He added, “Unlike electron microscopes, X-rays can observe internal structures without damaging the sample, thus potentially establishing a new standard for non-invasive nanoscale structure inspection, such as semiconductor inspection.”

This research was published on the 7th in the international journal of optics and photonics, Light: Science and Applications. (Paper title: Direct high-resolution X-ray imaging exploiting pseudorandomness).

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