A new x-ray microscope probes the inner intricacies of materials smaller than human cells and creates unparalleled high-resolution 3D images. By integrating unique automatic calibrations, scientists at the U.S. Department of Energy's Brookhaven National Laboratory are able to capture and combine thousands of images with greater speed and precision than any other microscope. The direct observation of structures spanning 25 nanometers - or 25 billionths of a meter - will offer fundamental advances in many fields, including energy research, environmental sciences, biology, and national defense.
This innovative full field transmission x-ray microscope (TXM), funded by the American Reinvestment and Recovery Act, was developed and commissioned at Brookhaven Lab's National Synchrotron Light Source (NSLS), which provides the x-ray source needed to capture images on the nanoscale. A new paper details the experimental success of a breakthrough system that rapidly combines 2D images taken from every angle to form digital 3D constructs.
"We can actually see the internal 3D structure of materials at the nanoscale," said Brookhaven physicist Jun Wang, lead author of the paper and head of the team that first proposed this TXM. "The device works beautifully, and it overcomes several major obstacles for x-ray microscopes. We're excited to see the way this technology will push research."
Building an Extra Dimension
Wang's team examined, for example, a 20-micrometer electrode from a lithium-ion battery - as thin around as a human hair. The internal interaction of pores and particles determines the energy performance of the battery, and examining that activity requires precise knowledge of the nanoscale structure.
Wang's team took 1,441 2D pictures of the electrode as a machine rotated the tiny material specimen to capture every possible angle. The challenge then becomes converting those separate images into a single 3D structure - one in which every nanometer makes a difference. On this scale, the usual one-micron wobbles are similar in scale to taking a portrait and having the subject leap several feet to either side.
Before this new system, scientists had to manually align every single image or use software to slowly interpret the shifts.
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This had two major limiting effects on the process: first, the sample has to have sharp internal features or be marked to provide guidelines, which can limit material types; and second, manual alignment demands so much time that the total image count peaks in the hundreds. Brookhaven's TXM changes that.
For the first time, the specimen is mounted on top of a platform with three sensors that measure nanometer shifts in any direction as the battery rotates and the microscope takes pictures. The computer recording the images, after calibration using a gold sphere, then automatically compensates for any shifts and accurately assembles the images into the final three-dimensional construct. The entire process takes only four hours, and that owes more to the x-rays available from NSLS than the microscope or computer.
Jun Wang, Yu-chen Karen Chen, Qingxi Yuan, Andrei Tkachuk, Can Erdonmez, Benjamin Hornberger, and Michael Feser : Automated markerless full field hard x-ray microscopic tomography at sub-50 nm 3-dimension spatial resolution, Appl. Phys. Lett. 100, 143107 (2012);
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