A new method that combines the advantages of X-rays and CT

Researchers from the US Department of Energy's Brookhaven National Laboratory in collaboration with scientists from Columbia University have succeeded in developing a new type of X-ray device - a way to peer into the real world of nanometer devices

Nanomaterials consisting of particles with sizes measured in billionths of a meter hold great promise for creating batteries, fuel cells, catalysts and drug delivery systems, which will be much more efficient than today. Observing the way in which these nanoscale materials change and react within the devices during their operation is essential in order to obtain insights that will allow further improvement of the performance of these devices. However, in most studies the scientists were able to look at perfect examples of the individual components, and not at their practical operation within an active device.

Now, a group of researchers from the US Department of Energy's Brookhaven National Laboratory in collaboration with scientists from Columbia University have succeeded in developing a new type of X-ray device - a way to peer into the real world of devices in order to map their internal nanostructures and properties of their various components, and even the change of the properties during the operation of the device. The new dual imaging method, described in detail in the scientific journal Nature Communications, combines high-intensity X-ray radiation acting on nanoscale structures along with obtaining cross-sectional "slices" of the device to identify the exact location of the nanoscale components. The new method opens a window to new opportunities for progress in a wide range of research fields, from materials science to biomaterials, geology, environmental science and medicine.

"If you think about a battery that includes an anode, which is next to a membrane, which is next to a solid electrolyte, next to another membrane, next to the cathode, when everything is wrapped in a steel container, this whole device is quite sealed from the outside view," explains Simon Billinge, one of the lead authors of The article and researcher at Columbia University and also at the National Laboratory. "What we can do now, with our new dual imaging method, is look inside the battery and extract an image of the nanostructures of each of the individual parts inside the battery, and we can do this without disassembling the battery, and during its normal operation, so you can monitor the chemical processes that take place inside it."

The x-rays used in the new method are not of the type often used to image a broken bone. Instead, the rays are powerful, have tiny beams and are able to produce very high energies thanks to a synchrotron light source (a type of particle accelerator, Synchrotron), a precise scientific device found in selected research centers around the world. The X-rays make it possible to measure the distances between pairs of atoms and this measurement makes it possible to determine the nanometer structure of the material being tested.

Large-scale cross-sectional images of slices of the material taken at multiple "photographic" angles using a computed tomography (CT) machine—similar to the machine doctors use to examine head injuries after a blow to the head—provide scientists with the spatial information they need to formulate XNUMXD mapping of the device components and "placing" the information about the nanometric structure on top of this mapping.

"Each of the separate methods (X-rays and CT) has its own power, but combining them together provides us with a completely new picture," notes the lead researcher. "For the first time ever, we can separate the signals of the nanostructures received from the different parts of an active device and see how the different atoms behave at each point, and all this without disassembling the device into its various components." Similar to other imaging methods that have had a decisive and major impact in the fields of health and the sciences of physiology and neurology, this method offers unprecedented access to the internal interrelationships of materials at the nanometer level.

In order to demonstrate the new method, the scientists made images of a complex structure of material that includes a mixture of several amorphous and semi-crystalline materials. The researchers were able to differentiate between the different types of components within the mixture very easily. In the next step, they used the method to examine the internal structure of a catalyst commonly used in the chemical industry, which consists of palladium nanoparticles fixed on a substrate of aluminum oxide. "The efficiency of many industrial processes depends on the performance of catalysts fixed on a structural substrate, and therefore, it is very important to understand how they are obtained and work in practice," explains the lead researcher.

The method was able to clearly show a non-uniform distribution of particles, with the larger particles being on top of the substrate and the smaller ones inside the material itself. "It is not clear from this study whether the significant catalytic activity is due to the larger and more numerous particles located in the periphery, or whether it is due to the smaller particles located in the center," says the researcher. "However, with the help of the use of our method, known as PDF-CT to monitor the catalyst during its activity, it is now possible to provide a more complete picture regarding the structure of the catalyst and the processes that go through it during its activity, and thus the interrelationships can be understood more clearly, and ultimately, the catalysts can be improved to be developed in the future."

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