A new method accelerates X-ray imaging of expanded samples such as microchips. The innovative technology makes it possible to study relatively large objects to nanometer-fine details in a reasonable time. It is not only interesting for science but also for industry, as the development team led by DESY researcher Mikhail Lyubomirskiy writes in the journal Scientific reports.
“X-rays have the power to reveal extremely small details,” says Lyubomirskiy. “But, X-rays are not as uncomplicated as optical camera photography.” There are no standard X-ray lenses and cameras. Instead, researchers often use a technique called psychography. It works without imaging lenses by scanning the sample in fine steps and registering how the X-rays are diffracted (scattered) by it. Ptychography can reach the highest possible resolution, but the step size during scanning must be smaller than the diameter of the X-ray, resulting in a large number of steps over an extended sample.
This often limits the sample size to the micrometer scale, for practical reasons. One micrometer is one thousandth of a millimeter. Many objects of interest to science and industry are much larger, for example in the millimeter regime as a microchip. Using beamline P06 at DESY’s PETRA III X-ray source, Lyubomirskiy’s team now found a seemingly obvious solution to the speed problem: using more than one beam to record multiple patterns simultaneously. But to do that, the researchers had to overcome a major obstacle: How to distinguish the diffraction patterns of the different rays?
“We developed a scheme where the identity of each beam is coded in its unique phase and shape,” explains Lyubomirskiy. Like a light wave, X-rays oscillate as they travel. The position of this periodic oscillation at a certain time or at a certain place is called the phase. The researchers made sure that each X-ray arrives at the sample with a different phase structure and shape. Unfortunately, X-ray detectors do not directly detect the phase of a wave reaching them. But in psychography, the properties of the scattering image depend on the phase structure that the X-ray has when it hits the sample. With a little smart mathematics, the researchers can distinguish the different diffraction pattern contributions from the corresponding phase-structured X-rays.
This innovative scheme accelerates photography considerably. “Essentially, twice as many rays halve the required time,” explains the DESY physicist. “For demonstration, we scanned a microchip with three beams that took about a third of the normal time.” For an area of 80 by 80 micrometers, the three-ray scan needed one and a quarter. The resulting image has a resolution of 95 nanometers (millionths of a millimeter). “In a later experiment, we have already used six rays, and the method can also be extended to nine or possibly twelve rays,” says Lyubomirskiy.
“The need to quickly image large samples with the highest spatial resolution exists in many areas of science and industry and will increase with future needs in materials design,” the authors write. They expect multi-beam ptychography to be useful for fast, high-quality imaging in many applications. As in catalytic research, for example, the authors and their collaborators recently received 1.2 million euros for four years in research funding from Röntgen Ångström Cluster (RÅC), a Swedish-German scientific collaboration. They will establish a framework for operandomicroscopy of catalytic reactions in PETRA III and MAX IV.
Researcher from the Center for X-ray and Nano Science CXNS at DESY, University of Hamburg, Lawrence Berkeley National Laboratory, MAX IV Laboratory at Lund University, Paul-Scherrer-Institut (PSI) in Switzerland, GSI Helmholtz Zentrum für Schwerionenforschung GmbH, XRnanotech GmbH and Helmholtz Imaging Platform participated in this research.
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