Microscopic Imaging Improved

To obtain sharp images using x-ray microscopy, instruments and samples must remain completely still, even at the nanometer scale, during the recording. Now, reliable images can be produced using a new method of interpretation that relaxes these tough restrictions.

X-ray microscopy requires radiation of extremely high quality. To visualize nanostructures such as biological cells, the porous structure of cement or storage fields of magnetic disks, investigators have had to avoid any kind of vibration or fluctuation in the x-ray microscope and sample. In addition, only a small fraction of the incoming x-ray radiation could be used. Special filters had to be used to select the exact fraction with the right properties — for example, the right wavelength.

Researchers at TUM and the Paul Scherrer Institute have developed a method that produces reliable images with x-ray microscopy in spite of vibrations or fluctuations. While the test object is moved through the x-ray beam with nanometer precision, a detector captures the scattered x-rays. The scattering images are then reconstructed to create an image of the sample. Images courtesy of TUM/ Paul Scherrer Institute, Villigen (Switzerland).

Pierre Thibault of Technical University Munich and Andreas Menzel of the Paul Scherrer Institute have now developed an interpretation method that produces reliable images in spite of vibrations or fluctuations. The method is based on a 1960s electron microscopy technique called ptychography. The researchers’ advancements now make it possible to distinguish the effects contributed by the different types of x-ray waves.

The study’s results give access to a whole class of objects that previously could hardly be investigated.

"We now not only can compensate for the vibrations in the microscope," Menzel said, "we can even characterize fluctuations of the sample itself, even if they are much too fast to be seen with individual snapshots."

"We needed to convince ourselves that the images we produced did indeed reflect accurately the samples and their dynamics," Thibault said. "So we carried out computer simulations. They confirmed that effects of the instrument as well as of the sample itself, such as flows, switching events or mixed quantum states, can be characterized."

Compared to a recording using conventional technology (left), ptychographic processing greatly improves the quality of the x-ray microscopic image (right).

The new method combines the characterization of dynamical states with high-resolution x-ray microscopy. One possible application is to analyze the changing magnetization of individual bits in magnetic storage media with high storage density. The interactions of such single magnetic bits or their thermal fluctuations, which ultimately determine the lifetime of magnetic data storage, could be visualized.

"In addition to its use in imaging," Thibault said, "our analysis method also reveals a fundamental relationship to other disciplines: Microscopy and scientific disciplines such as quantum computing, previously regarded as independent, can benefit from each other here."

The study was published in Nature (doi: 10.1038/nature11806).

For more information, visit: www.tum.de or www.psi.ch