This article covers a collaborative breakthrough in resonant inelastic X-ray scattering (RIXS) within the tricky tender X-ray range of 2–3 keV. Conventional gratings have always struggled to deliver high efficiency there.
Researchers from Diamond Light Source, Tongji University, and the University of Science and Technology of China have now shown that a lateral-graded multilayer grating (MLG) can dramatically boost diffraction efficiency across 2–3 keV. This enables much faster data collection and finally bridges soft and tender X-ray capabilities on a single instrument.
Overview of the breakthrough
The team tackled a long-standing bottleneck in tender X-ray RIXS by engineering a grating that adapts to the changing incidence angle across its surface. They deposited lateral-graded multilayer coatings onto a spherical variable-line-spacing (VLS) grating.
With this setup, they matched the generalized Bragg condition at each position along the grating. That means a high, position-dependent d-spacing preserves constructive interference for X-rays as they diffract.
The result? Strong, uniform efficiency where conventional single-layer coatings just can’t keep up.
Lateral-graded multilayer design
Key innovations include seamlessly integrating three distinct lateral-graded multilayers onto the same VLS grating. This enables full coverage of the tender X-ray band (2–3 keV).
The multilayer spacing changes laterally to compensate for the varying angle of incidence, so the Bragg condition is satisfied across the surface. This approach sidesteps the limited Darwin width and low efficiency that plague traditional optics in this energy range.
Three main design choices made this work: lateral grading of the multilayer period, matching to the grating’s surface geometry, and tailored material stacks to optimize reflection at 2–3 keV. The result is an MLG that finally breaks the old efficiency barrier and pushes grating performance into the tender X-ray domain.
Performance gains and experimental data
Measured results show an efficiency of about 60% at 2.8 keV for the MLG. That’s a huge leap over what anyone’s managed in this region before.
Across the 2–3 keV range, the MLG delivers efficiency enhancements ranging from 12- to 25-fold compared to traditional coatings. These gains lead directly to faster data collection—RIXS acquisition times drop from hours to minutes.
Efficiency, speed, and energy coverage
The benefits aren’t tied to just one energy. The three designed lateral-graded multilayers work together to provide broad coverage of the tender band (2–3 keV) with high reflectivity.
They also keep compatibility with the spherical VLS grating geometry. This combination unlocks high signal-to-noise RIXS measurements on tricky 4d transition-metal systems and similar materials, where tender X-rays are essential to probe electronic structure and excitations.
Broader implications for X-ray science
With the MLG in place, the I21 RIXS spectrometer at Diamond Light Source becomes the first grating-based facility to span both soft and tender X-ray regions (roughly 280–3000 eV).
Having this unified spectral capability on a single instrument could shake up materials science, catalysis, and condensed-matter physics. Now researchers can directly compare soft- and tender-X-ray excitations without swapping out beamline optics.
Impact on Diamond and other beamlines
The authors think applying MLGs to beamline monochromators could further boost photon flux and experimental efficiency. There’s even potential for more: increasing grating line density or using higher diffraction orders might raise resolving power while keeping high efficiency, paving the way for high-resolution tender RIXS and related spectroscopies.
The MLG concept could extend to other X-ray spectroscopy techniques, hinting at a possible platform upgrade for a bunch of research programs. It’s an exciting time for X-ray science—maybe even overdue.
Future directions
Looking ahead, researchers want to try integrating MLGs into more beamlines. They’re also thinking about tweaking multilayer materials to push performance across a wider range of energies.
Next up, the team plans to optimize multilayer stacks for better diffraction efficiency. They’re curious about using higher line densities to boost spectral resolution, and they’re aiming for real-world deployment in monochromators.
All this could speed up experiments in chemistry, physics, and materials science. Fast, high-flux tender X-ray measurements might open doors to insights we haven’t even imagined yet.
Here is the source article for this story: TRIXS: A multilayer grating solution towards highly efficient resonant inelastic tender X-ray scattering