The new system delivers a dramatic improvement in photon detection efficiency, outperforming conventional wavelength-dispersive X-ray emission spectrometers by a factor of 100 to 1000. Researchers plan to use it to study the electronic properties of atomically thin materials, nanostructures, and highly diluted atomic and molecular samples. The team is now inviting research proposals from the scientific community.

Bringing Greater Sensitivity to X-Ray Spectroscopy

Facilities such as BESSY II generate extremely bright and intense synchrotron X-rays that allow scientists to analyze a wide range of materials. Yet techniques such as X-ray emission spectroscopy (XES) and Resonant Inelastic X-ray Scattering (RIXS) face a significant challenge. Because these methods rely on detecting photons emitted by the sample, they require large numbers of photons to produce useful measurements.

As a result, XES and RIXS experiments have traditionally been limited to concentrated samples and bulk materials.

"The superconducting Transition Edge Sensor (TES) array photon detector that we have now put into operation at BESSY II is around 100 to 1000 times more efficient to detect photons than conventional XES and RIXS spectrometers," says Régis Decker, HZB, responsible scientist of the new instrument.

Exploring Quantum Materials and Ultra-Thin Systems

The increased sensitivity opens the door to experiments that were previously difficult or impossible to perform.

"This can provide new insights into molecular chemistry or molecular biology, but also into the quantum properties of systems in reduced dimension such as atomic monolayers, nanostructures and impurities. The TES spectrometer complements methods such as ARPES, which scans the electronic band structures of such systems," says Régis Decker.

The instrument can also dramatically reduce data collection times. Some XES and RIXS experiments that would normally require hours can now be completed in just minutes.

248 Superconducting Sensors Working Near Absolute Zero

At the heart of the TES array spectrometer are 248 sensors that become superconducting when cooled to 25 milli-Kelvin. To achieve this temperature, researchers use a He4-He3 dilution refrigerator similar to those employed in quantum computing systems.

When X-rays interact with a sample, the sample emits photons. These photons strike individual sensors within the TES array, producing a sudden increase in temperature. That brief warming disrupts the superconducting state and increases the sensor's electrical resistance. The change is then measured using circuitry based on an array of Superconducting Quantum Interference Devices (SQUIDs).

Advanced Sample Handling and Future Upgrades

The spectrometer is connected to a custom ultra-high vacuum sample chamber that supports sample transfer, preparation, and measurement. The chamber also provides precise temperature control ranging from 10 K to room temperature.

The complete system is installed at the BESSY II UE52-SGM beamline, which offers full polarisation control. Planned upgrades include enhanced sample preparation capabilities and the ability to study materials in magnetic fields for X-ray Magnetic Circular Dichroism in absorption (XMCD) and emission (RIXS-MCD).

Europe's Only Synchrotron TES Spectrometer

TES spectrometers were originally created for astrophysics applications, where detecting extremely weak photon signals is essential. Before the installation at BESSY II, only five TES spectrometers were operating at X-ray facilities worldwide, including four in the United States and one in Japan.

BESSY II now hosts the only synchrotron TES spectrometer in Europe.

"We are looking forward to receiving exciting research proposals from our user community," says Decker.