Superconducting TES array X-ray spectrometer goes into operation at BESSY II
The superconducting sensors need a temperature below 25 milli Kelvin. This is achieved by using a He4-He3 dilution refrigerator, pictured here. It is similar to those used for quantum computers. © Régis Decker / HZB
The photo shows the detector array, composed of 248 sensors. © Régis Decker / HZB
Europe's first and only TES-spectrometer at a synchrotron source is now in operation at BESSY II, developed within a collaboration between the HZB, the MPI-CEC (Mühlheim-an-der-Ruhr, Germany) and the NIST (Boulder CO, USA). The photon detection efficiency of the new instrument exceeds that of wavelength-dispersive X-ray emission spectrometers by a factor of 100 to 1000. It will be used to investigate the electronic properties of atomically thin layers, nanostructures and highly diluted atomic and molecular samples. The team is looking forward to receiving exciting research proposals from the user community.
Synchrotron radiation sources such as BESSY II provide intense, highly brilliant X-ray light that can be used to examine a wide variety of samples. However, X-ray emission spectroscopy (XES) and Resonant Inelastic X-ray Scattering (RIXS), where the photons emitted from the sample are detected, are extremely photon-hungry techniques. Therefore, XES and RIXS have been so far largely limited to high concentration and bulk samples.
Huge sensitivity
‘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.
Low-dimensional systems
‘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. In addition, some XES and RIXS measurements that would otherwise take hours can be completed in a matter of minutes using this instrument.
248 superconducting sensors
The TES array spectrometer contains 248 sensors that are superconducting when cooled at 25 milli-Kelvin. Such a low temperature is reached using a He4-He3 dilution refrigerator, similar to those used for quantum computers. When a sample is examined with X-rays, it reacts by emitting photons itself. These photons then strike individual sensors in the array, causing an abrupt rise in temperature that briefly destroys the superconducting state leading to an increase of the resistance of the sensor, detected through a circuit based on an array of Superconducting Quantum Interference Devices (SQUIDs).
The spectrometer is attached to a custom ultra-high vacuum sample chamber, which enables the transfer, preparation and measurements of samples with precise temperature control from 10 K to room temperature. The ensemble of spectrometer and sample chamber is installed at the BESSY II UE52-SGM beamline, which allows full polarisation control. Future developments include improvements of the sample preparation capabilities and measurements of samples in magnetic field for X-ray Magnetic Circular Dichroism in absorption (XMCD) and emission (RIXS-MCD).
Europe's only TES-spectrometer
TES spectrometers were originally developed for astrophysical measurements to enable even the weakest photon fluxes to be evaluated. Until now, only five TES spectrometers worldwide existed at X-ray sources, four of them in the USA and one in Japan. BESSY II hosts now the only synchrotron TES spectrometer in Europe. ‘We are looking forward to receiving exciting research proposals from our user community,’ says Decker.
- Perovskite triple-junction solar cells: Even more efficient with GO/SAM bilayersPerovskite semiconductors efficiently convert sunlight into electrical energy; they are also inexpensive and extremely lightweight. A team at HZB has developed a triple-junction solar cell comprising different perovskite semiconductors, with a novel bilayer of graphene oxide (GO) and a self-assembled monolayer (SAM) as the hole conductor. This bilayer significantly increases both efficiency and long-term stability. The efficiency of the novel perovskite triple-junction solar cell is 27.3% and shows hardly any decline even after more than 770 hours of operation. The study has been published in the renowned journal Joule.
- Magnetic imaging: Micro-flowers increase the local magnetic fieldMaterials with magnetic nanostructures have many potential applications such as in spintronics. To explore such materials, nanoscale magnetic-sensitive imaging techniques are very useful, but up to now only weak magnetic fields could be applied during the imaging process. Now an international collaboration led by Dr. Sergio Valencia, HZB, has developed an approach that overcomes this limitation. The team designed tiny magnetic flux concentrators (MFCs), into which the sample is placed. The geometry of the MFCs resembles a flower with a number of petals which focus the applied magnetic field into its center. This greatly expands the magnetic field range available during imaging, and so the range of magnetic systems that can be investigated. The micro-flowers, enhancing magnetic fields locally, can find application in different nanometric magnetic microscopy techniques.
- CIGS-perovskite tandem cell achieves record efficiency of 25.5 %A Berlin-based team from HZB and Center for the Science of Materials Berlin (CSMB) at the Humboldt-Universität zu Berlin has set a new record for a tandem solar cell. Using a combination of a CIGS semiconductor layer and perovskite, along with several optimised intermediate layers, they were able to convert 25.5% of sunlight into electrical energy. The previous record for this combination of materials and this size of cell stood at 24.6%. The new record has been certified and is visible in the prestigious Solar Cell Efficiency Tables (the "Green Tables"), which serve as the definitive ledger for the global photovoltaic community.