X-rays probe structural properties of solids

A new method uses x-rays to probe the properties of solid materials without destroying them, which could mean big things for superconductivity and chemistry studies.

X-ray scattering and x-ray emission spectroscopy are powerful techniques – often too powerful, damaging samples or losing measurable signals. But x-ray free-electron lasers combine the optical properties of lasers with the analytic power of x-rays, enabling damage-free probing of solid materials. Inducing stimulated x-ray emission from a solid sample provides a superior probe for low-energy excitation and dispersion in matter.

Researchers at the Helmholtz Center Berlin have documented how inelastic scattering can be intelligently intensified so that a shift of frequency is observed. Photo courtesy of ©HZB/E. Strickert.

A team at the Helmholtz Center Berlin, led by Dr. Martin Beye and professor Alexander Föhlisch, showed that solids lend themselves to x-ray analysis based on nonlinear physical effects. Until now, this could only be done using lasers, previously thought to be unhelpful in x-ray analysis. The physics of x-ray methods is based on linear effects, meaning that each photon works in isolation.

But photons actually work together under laser light, and nonlinear effects result from their interaction with matter. Certain materials enhance certain colors of light, as when an irradiated crystal takes in green light and then expels red light. The color can be correlated with the structural properties of the analyzed material.

“Our experiment allowed us to document how inelastic x-ray scattering can be intelligently intensified,” Beye said. “Just like a laser, the different photons are actually working together and amplifying each other, and we end up with a very high measurement signal.”

This development holds strong appeal for superconductivity development, chemical bond studies or inelastic scattering processes that focus on element-specific investigations.

“With the current results, we know that we can use nonlinear effects even with soft x-ray radiation,” Föhlisch said. “What we need are photon sources capable of delivering short light pulses in rapid succession. This has to be taken into consideration during future photon source development.”

The work appeared in Nature (doi: 10.1038/nature12449).