SPring-8, the large synchrotron radiation facility

A research group successfully demonstrated that high-resolution X-ray imaging can be applied to thick objects, which previously was impossible by conventional methods. The group was led by Yukio Takahashi (associate professor) and Akihiro Suzuki (1st year Ph.D. student, fellow of Japan Society for the Promotion of Science) of the Graduate School of Engineering, Osaka University, and Tetsuya Ishikawa (Director) of RIKEN SPring-8 Center.

X-rays exhibit high transmittance and can be used to observe the internal structure of even thick objects. They are electromagnetic waves with a wavelength on the angstrom (Å) order (1 Å is one-ten-billionth of a meter). Hence, the development of a high-resolution X-ray microscope is possible in principle. However, the high-resolution observation of the inside of thick objects is not easy. In X-ray imaging, projection approximation is generally adopted, in which a specimen is projected in the direction of X-ray propagation and approximated to a very thin object. A thick object, however, cannot be observed at a high resolution by this method because X-ray wavefronts change in the specimen. To address this issue, the research group adopted a multislice approach^*1 and demonstrated the validity of X-ray ptychography^*2 by this approach for the first time in the world. In the multislice approach, a specimen is modeled as an accumulation of thin layers perpendicular to incident X-rays, and the changes in X-ray wavefronts between the layers are measured. Multislice X-ray ptychography performed at SPring-8^*3 revealed that a resolution of ~50 nm (1 nm is one-billionth of a meter), much better than the limit under the projection approximation (192 nm), was achieved for a specimen with a thickness of 105 μm (1 μm is one-millionth of a meter).

The demonstrated multislice X-ray ptychography enables the observation of nanostructures and tissues in thick objects. It can be applied to the nondestructive high-resolution three-dimensional observation of, for example, the nanowiring of integrated circuits and biological bone tissue.

The achievements of this research were published online in the American scientific journal Physical Review Letters on 4 February 2014.

Publication:
"High-resolution multislice x-ray ptychography of extended thick objects"
Akihiro Suzuki, Shin Furutaku, Kei Shimomura, Kazuto Yamauchi, Yoshiki Kohmura, Tetsuya Ishikawa, Yukio Takahashi
Physical Review Letters 112 053903, Published 4 February 2014.