#SynchroLightAt75 – X-ray detector technology

X-Ray detectors first developed at Paul Scherrer Institute PSI in the 1990s to aid the search for the Higgs Boson at CERN and then applied to the Swiss Light Source SLS led to the spin-off, Dectris. Today this company employs over 100 people and its cutting-edge detectors are used at synchrotron and free electron laser (FEL) light sources worldwide for diverse applications ranging from protein structure determination to investigations into novel materials.

As the light source community marks #SynchroScienceAt75, we look back on this fascinating chapter in the history of light sources….

From the Higgs boson to new drugs (story published by PSI in 2016)

New ultrafast detector at the Paul Scherrer Institute

A picture-perfect example of how basic research makes solid contributions to the economy is the company DECTRIS in Baden-Dättwil, Switzerland — a spin-off of the Paul Scherrer Institute PSI, founded in 2006 and already highly successful. The detector that became, around ten years ago, the company’s founding product originated in the course of the search for the Higgs boson. Now the newest development from DECTRIS is on the market: an especially precise detector called EIGER, which is used for X-ray measurements at large research facilities. Since the fall of 2015, the newest model of the EIGER series has proven itself at the Swiss Light Source SLS. These days, researchers are writing the first scientific publications about experiments that have been carried out with the new detector. EIGER helps researchers to measure protein molecules better and more precisely than before. That in turn is of great interest for the development of new pharmaceuticals. It’s possible that urgently needed alternatives to antibiotics might be found in this way.

Read more on the PSI website

Image: PSI scientist Justyna Wojdyla and DECTRIS engineer Michel Stäuber with the EIGER X 16M – the spin-off company’s newest and, so far, highest-performance X-ray detector (caption from 2016)

Credit: Scanderbeg Sauer Photography

New angle for perovskite research

Perovskite materials offer the potential for cheaper optoelectronic devices such as solar cells. Of these, the formamidinium (FA)-based FAPbI3 crystal is one of the most promising – it has a bandgap close to ideal and is very thermally stable. However, photoactive cubic (α)-FAPbI3 perovskite phase is highly unstable and quickly transforms into the non-perovskite yellow phase at room temperature in ambient atmosphere, which affects the performance of photovoltaic devices. Alloying of FA-based perovskite with caesium, methylammonium (MA) cations or a combination of both can keep the perovskite in its more efficient phase at lower temperatures. However, this can give patchy results, leading to power losses.

In work recently published in Science, researchers from the University of Cambridge Department of Chemical Engineering and Biotechnology (CEB) and the Cavendish Laboratory investigated the crystal structure of the alloyed perovskite materials to understand why adding cations improved their performance. Their results show that cation alloying induces a minor octahedral tilt that keeps the perovskite material in its highly efficient phase, and is a step towards commercial production of stable and efficient perovskite-based solar cells. 

A small distortion makes a big difference

Formamidinium (FA)-based perovskites have much better thermal stability than the methylammonium (MA)-based absorber layers commonly used in early perovskite-based solar cells. FAPbI3 is a particularly promising material, but its photoactive phase is only stable at high temperatures (above 150ºC) in inert atmosphere. It transitions to a hexagonal phase with poor optoelectronic performance at lower temperatures.  

It has been shown empirically that alloying FAPbI3 with methylammonium (MA) cations or caesium (or both) improves stability. However, although this approach led to record efficiencies, the mechanism underlying it was not fully understood. It also produces uneven materials with patches of instability that lead to performance losses. 

Co-lead author Tiarnan Doherty was a PhD student at the Cavendish Laboratory and is now an Oppenheimer Fellow in CEB. He says:

We wanted to investigate the atomic structure of the alloyed perovskite materials, but they’re very sensitive to damage. So we brought the samples to ePSIC for high-resolution electron microscopy with a low electron dose. We also used nano X-ray diffraction on beamline I14. That beamline has very sensitive detectors, which allowed us to achieve our results using low X-ray exposures.

Read more on the Diamond website

Image: Artist’s impression of formamidinium (FA)-based crystal

Credit: Tiarnan Doherty, University of Cambridge

Diamond-II programme set to transform UK science

Diamond Light Source has established itself as a world-class synchrotron facility enabling research by leading academic and industrial groups in physical and life sciences. Diamond has pioneered a model of highly efficient and uncompromised infrastructure offered as a user-focussed service driven by technical and engineering innovation.

To continue delivering the world-changing science that Diamond leads and enables, Diamond-II is a co-ordinated programme of development that combines a new machine and new beamlines with a comprehensive series of upgrades to optics, detectors, sample environments, sample delivery capabilities and computing. The user experience will be further enhanced through access to integrated and correlative methods as well as broad application of automation in both instrumentation and analysis. Diamond-II will be transformative in both spatial resolution and throughput and will offer users streamlined access to enhanced instruments for life and physical sciences.

Read more on the Diamond website

Image: Diamond’s synchrotron building

Credit: Diamond Light Source

Looping X-rays to produce higher quality laser pulses

A proposed device could expand the reach of X-ray lasers, opening new experimental avenues in biology, chemistry, materials science and physics.BY ALI SUNDERMIER

Ever since 1960, when Theodore Maiman built the world’s first infrared laser, physicists dreamed of producing X-ray laser pulses that are capable of probing the ultrashort and ultrafast scales of atoms and molecules.

This dream was finally realized in 2009, when the world’s first hard X-ray free-electron laser (XFEL), the Linac Coherent Light Source (LCLS) at the Department of Energy’s SLAC National Accelerator Laboratory, produced its first light. One limitation of LCLS and other XFELs in their normal mode of operation is that each pulse has a slightly different wavelength distribution, and there can be variability in the pulse length and intensity. Various methods exist to address this limitation, including ‘seeding’ the laser at a particular wavelength, but these still fall short of the wavelength purity of conventional lasers.

Read more on the SLAC National Accelerator Laboratory website

Image: Schematic arrangement of the experiment. The researchers send an X-ray pulse from LCLS through a liquid jet, where it creates excited atoms that emit a pulse of radiation at one distinct color moving in the same direction. This pulse is reflected through a series of mirrors arranged in a crossed loop. The size of this loop is carefully set so that the pulse arrives back at the liquid jet at the same time as a second X-ray pulse from LCLS. This produces an even brighter laser pulse, which then takes the same loop. The process is repeated several times, and with each loop the laser pulse intensifies and becomes more coherent. During the last loop, one of the mirrors is quickly switched allowing this laser pulse to exit.

Credit: (Greg Stewart/SLAC National Accelerator Laboratory)