Technique expands range of x-ray research

Ashley N. Rice, ashley.rice@photonics.com

A new technique takes much of the “guesswork” out of x-ray imaging by combining high-resolution and 3-D viewing, allowing the surface of materials to be viewed nondestructively for the first time. The findings expand the range of x-ray research possible for biology, nanophotonics and nanoelectronics.

“This is the future of how we will visualize structure of surfaces and interface structures in materials science with x-rays,” said Argonne scientist Jin Wang, lead author of the study, which appeared online in Nature Photonics (doi: 10.1038/nphoton.2012.178).

Conventional x-ray imaging techniques allow for 3-D structural rendering, but at a lower image resolution, resulting in greater uncertainty. In some cases, the x-rays’ intensity can destroy the sample.

The new technique, developed by x-ray scientists from the Advanced Photon Source (APS) and Center for Nanoscale Materials at the US Department of Energy’s Argonne National Laboratory, blends the advantages of 3-D surface viewing from grazing-incident geometry scattering with the high-resolution capabilities of lensless x-ray coherent diffraction imaging (CDI) to image samples with a single nondestructive x-ray shot. An adaptation of existing detector technology, the technique reduces “guesswork” by eliminating the need for modeling-dependent structural simulation often used in x-ray analysis. It is expected to work at all x-ray light sources.

Wang and colleagues brought the 3-D power of the new imaging technique to the surface layers of the sample by adjusting the angle at which the x-rays scatter off samples. Most of the atomic interactions that control the functionality and efficiency of a product, such as a semiconductor or self-assembled nanostructure, occur at or just below the surface. Without direct 3-D viewing capabilities, scientists must rely on models to estimate a surface structure’s thickness and form, weakening confidence in the estimate’s accuracy.

The technique expands CDI viewing from the nanometer to the millimeter scale when the x-ray beamline impinges on the sample at a glancing angle. This enables scientists to relate the behavior of a bundle of atoms or molecules to that of an entire device.

This area – the mesoscale, between nanoresearch and applied technology – has been a particularly difficult one for scientists to access. In nanotechnology, this area is thought to hold promise for making stronger, more flexible and more efficient materials. In biology, it connects intercellular behavior with the activity of individual cells and the larger organism.

“Hopefully, this technique will be applied to research in biology, microelectronics and photonics,” said Tao Sun, a postdoctoral research fellow working at the APS and the first author on the research. “This technique holds great promise because the resolution we can reach is only limited by wavelength, a fraction of a nanometer.

“So the APS upgrade and other advances in light source and detector technology will easily provide even higher-resolution images than we have achieved in this work.”