NSLS-II scientists see around hidden corners of tiny objects, even when significant portions of data are missing
X-ray tomography is a powerful tool that enables scientists and engineers to peer inside of objects in 3D, including computer chips and advanced battery materials, without performing anything invasive. It’s the same basic method behind medical CT scans. Scientists or technicians capture X-ray images as an object is rotated, and then advanced software mathematically reconstructs the object’s 3D internal structure. But imaging fine details on the nanoscale, like features on a microchip, requires a much higher spatial resolution than a typical medical CT scan — about 10,000 times higher.
The Hard X-ray Nanoprobe (HXN) beamline at the National Synchrotron Light Source II (NSLS-II), a U.S. Department of Energy (DOE) Office of Science user facility at DOE’s Brookhaven National Laboratory, is able to achieve that kind of resolution with X-rays that are more than a billion times brighter than traditional CT scans.
Tomography only works well when these projection images can be taken from all angles. In many real-world cases, however, that’s impossible. For example, scientists can’t spin a flat computer chip around 180 degrees without blocking some of the X-rays. When parallel to the surface at high angles, fewer X-rays can penetrate the chip, limiting the viewing angles of the measurement. The missing data from this angular range produces a “blind spot,” leading the reconstruction software to produce blurry, distorted images.
“We call this the ‘missing wedge’ problem,” said Hanfei Yan, lead beamline scientist at the HXN beamline and corresponding author of this work. “For decades, this problem has limited the applications of X-ray and electron tomography in many areas of science and technology.”
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Image: This 3D image of an integrated circuit showing slices through its thickness was reconstructed with a new technique that incorporates artificial intelligence called the “perception fused iterative tomography reconstruction engine.”
Credit: Brookhaven National Laboratory