A new x-ray microscope probes the internal structures of materials smaller than human cells and creates unparalleled high-resolution, three-dimensional (3D) images. By integrating unique automatic calibrations, scientists at Brookhaven National Laboratory are able to capture and combine thousands of images with greater speed and precision than any other microscope. As reported in the April 2 issue of Applied Physics Letters (DOI: 10.1063/1.3701579; 143107), this full-field transmission x-ray microscope (TXM) rapidly combines two-dimensional (2D) images taken from every angle to form digital 3D constructs. The direct observation of structures spanning 25 nm will offer fundamental advances in many fields, including energy research, environmental sciences, biology, and national defense, according to the scientists.

“We can actually see the internal 3D structure of materials at the nanoscale,” said Jun Wang, lead author of the article and head of the team that first proposed this TXM.

Wang’s team specifically examined a 20-μm-wide sintered LiCoO₂ electrode from a lithium-ion battery, wherein the energy performance of the battery is related to the internal connectivity of the pores and particles within the electrode. The researchers took 1441 2D pictures of the electrode as the material was rotated to capture every possible angle. These separate images were then combined to generate a single 3D construct of the specimen.

The three-dimensional reconstruction of a lithium-ion battery electrode, composed of 1441 individual images captured and aligned by the transmission x-ray microscope, reveals nanoscale structural details to help guide future energy research.

It is this reconstruction process that has previously limited the widespread application of transmission x-ray microscopy to nanotomography. Traditional methods require manual alignment of each 2D projection, or use software to slowly interpret the shifts. To achieve this, the sample has to have sharp internal features or be marked to provide guidelines, which can place restrictions on the materials that can be studied in this way. Such manual alignment procedures are extremely time-consuming, which limits the number of 2D images that can be employed, leading to reduced resolution of the final 3D images.

With the TXM, the specimen is mounted on top of a platform with three sensors that measure nanometer shifts in any direction as the sample 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 3D construct. The process takes only four hours, which owes more to the x-rays available from a synchrotron source than the microscope itself or the computer speed.

While this work has focused on alternative energy fuels and storage solutions, the new technology associated with this TXM will undoubtedly lead to its widespread use in examining biological, environmental, and materials samples.