Thank You SLS

Since 2001, the Swiss Light Source SLS has been a catalyst for ground-breaking discoveries in physics, materials science, biology, and chemistry. The extremely bright X-ray light provided by the SLS has enabled researchers to take giant leaps in their understanding of the world around us.

Countless scientists in Switzerland and worldwide have collaborated at this remarkable facility, pushing the boundaries of scientific knowledge and unlocking new possibilities. As we approach the temporary shutdown for the SLS 2.0 upgrade, our beamline scientists look back on 22 years of brilliant science and achievements made possible by the SLS.

Read more on the PSI website

Image: Aerial veiw of the Swiss Light Source

Credit: PSI

Tender X-rays show how one of nature’s strongest bonds breaks

Short flashes of an unusual kind of X-ray light at SwissFEL and SLS bring scientists closer to developing better catalysts to transform the greenhouse gas methane into a less harmful chemical. The result, published in the journal Science, reveals for the first time how carbon-hydrogen bonds of alkanes break and how the catalyst works in this reaction.

Methane, one of the most potent greenhouse gases, is being released into the atmosphere at an increasing rate by livestock farming as well as the continuing unfreezing of permafrost. Transforming methane and longer-chain alkanes into less harmful and in fact useful chemicals would remove the associated threats, and in turn make available a huge feedstock for the chemical industry. However, transforming methane necessitates as a first step the breaking of a C-H bond, one of the strongest chemical linkages in nature.

Forty years ago, molecular metal catalysts were discovered that can easily split C-H bonds. The only thing found to be necessary was a short flash of visible light to “switch on” the catalyst and – bafflingly – the strong C-H bonds of alkanes passing nearby were easily broken almost without using any energy. Despite the importance of this so-called C-H activation reaction, it has remained unknown how that catalyst performs this function. Now, experiments at Swiss FEL and SLS have enabled a research team led by scientists at Uppsala University to directly watch the catalyst at work and reveal how it breaks the C-H bonds.

Read more on the PSI website

Image: An X-ray flash illuminates a molecule

Credit: University of Uppsala / Raphael Jay

Mirror, mirror on the wall…

…. Now we know there are chiral phonons for sure

Findings published in Nature settle the dispute: phonons can be chiral. This fundamental concept, discovered using circular X-ray light, sees phonons twisting like a corkscrew through quartz.

Throughout nature, at all scales, you can find examples of chirality – or handedness. Imagine trying to eat a sandwich with two hands that were not enantiomers – non-superimposable mirror images – of each other. Consider the pharmacological disasters caused by administering the wrong drug enantiomer or, at a subatomic scale, the importance of the concept of parity in particle physics. Now, thanks to a new study led by researchers at PSI, we know that phonons can also possess this property.

A phonon is a quasiparticle that describes the collective vibrational excitations of the atoms in a crystal lattice; imagine it as the Irish Riverdance of the atoms. Physicists have predicted that if phonons can demonstrate chirality they could have important implications on the fundamental physical properties of materials. With the rapid rise in recent years of research into topological materials that exhibit curious electronic and magnetic surface properties, interest in chiral phonons has grown. Yet, experimental proof for their existence has remained elusive.

What makes phonons chiral is the steps of their dance. In the new study, the atomic vibrations dance a twist that moves forwards like a corkscrew. This corkscrew motion is one of the reasons there has been such a drive to discover the phenomenon. If phonons can revolve in this way, like the coil of wire that forms a solenoid, perhaps they could create a magnetic field in a material.  

A new slant on the problem

It is this possibility that motivated the group of Urs Staub at PSI, who led the study. “It is because we are at the juncture between ultrafast X-ray science and materials research that we could approach the problem from a different angle,” he says. The researchers are interested in manipulating chiral modes of materials using chiral light – light that is circularly polarised.

It was using such light that the researchers could make their proof. Using quartz, one of the best-known minerals whose atoms – silicon and oxygen – form a chiral structure, they showed how circularly polarised light coupled to chiral phonons. To do this, they used a technique known as resonant inelastic X-ray scattering (RIXS) at the Diamond Light Source in the UK. This was complemented with supporting theoretical descriptions of how the process would create and enable the detection of chiral phonons from groups at the ETH Zurich (Carl Romao and Nicola Spaldin) and MPI Dresden (Jeroen van den Brink).

Read more on the PSI website

Image: To prove the existence of chiral phonons, researchers used resonant inelastic X-rays scattering (RIXS). Circularly polarised light shines on quartz. The angular momentum of the photons is transferred to a crystal, causing a revolution in this case of anions (orange spheres with p orbitals) relative to their neighbouring cations (green spheres).

Credit: Paul Scherrer Institute / Hiroki Ueda and Mahir Dzambegovic

PSI researchers use extreme UV light to produce tiny structures for information technology.

Researchers at PSI have refined a process known as photolithography, which can further advance miniaturisation in information technology.

In many areas of information technology, the trend towards ever more compact microchips continues unabated. This is mainly because production processes make it possible to achieve ever smaller structures, so that the same number of information-processing components takes up less and less space. Fitting more components into less space increases the performance and lowers the price of the microchips used in smartphones, smartwatches, game consoles, televisions, Internet servers and industrial applications.

A research group led by Dimitrios Kazazis and Yasin Ekinci at the Laboratory for X-ray Nanoscience and Technologies at the Paul Scherrer Institute PSI, in collaboration with researchers from University College London (UCL) in the UK, has now succeeded in making important progress towards further miniaturisation in the IT industry. The scientists have demonstrated that photolithography – the method of patterning widely used in the mass production of microchips – works even when no photosensitive layer has been applied to the silicon.

Photolithography, which literally means “drawing on stone with light”, is the most important process in the industrial manufacture of electronic components. In principle, it works like exposing a photographic film to light, except that the carrier material is silicon rather than celluloid. A light-sensitive material, technically known as a photoresist, is applied to a silicon wafer. This is exposed to light in the pattern of the blueprint for the chip, which alters the chemical properties of the photoresist. This either becomes firmer or less firm. Subsequent treatment removes the exposed (positive process) or the unexposed (negative process) areas, leaving behind the desired circuit pattern, including the conductive traces. At present, this process is mainly carried out using lasers with a wavelength of around 240 to 193 nanometres.

However, the PSI researchers took a different approach. They opted against a photoresist, which degrades the image and is therefore an obstacle to miniaturisation.

Read more on the PSI website

Image: The PSI researchers involved at the XIL-II beamline of the SLS. From left to right: Yasin Ekinci, Gabriel Aeppli, Matthias Muntwiler, Procopios Christou Constantinou, Dimitrios Kazazis, Prajith Karadan

Credit: Paul Scherrer Institute/Mahir Dzambegovic

International Day of Light #LightSourceSelfie special from the SLS

A community driven by curiosity!

To celebrate International Day of Light 2023, we bring you a #LightSourceSelfies special (see below) from Ludmila Leroy, a postdoc at the Swiss Light Source (SLS), which is located at the Paul Scherrer Institut (PSI) in Villigen, Switzerland. With an energy of 2.4 GeV, the SLS provides photon beams of high brightness for research in materials science, biology and chemistry.

Ludmila, who is from Brazil, is studying the properties of magnetic materials. She highlights the versatility of light sources as hugely advantageous to science and learning from, and about, nature. “We are all driven by curiosity and these versatile facilities gives us the ability to try different approaches and push the boundaries in our experiments.” Looking back on her career to date, Ludmila would advise her younger self “not to be scared to reach out for the world” as there are many light sources facilities around the globe and travelling to different countries is an exciting part of being a scientist.

As with all light sources, the SLS operates around the clock and Ludmila has a new take on making night shifts more bearable. Throughout the #LightSourceSelfie campaign, most participants have mentioned coffee, chocolate or candy when talking about night shift survival strategies. For Ludmila, night shifts are more bearable when she eats healthily and makes sure that she keeps hydrated.

And when she is not at a light source….Ludmila is in charge of the Music Club at PSI, which brings together a mixture of PhD students, postdocs, technicians and staff scientists. The PSIchedelics is just one of the society’s musical entertainment offerings. Ludmila plays the bass and sings in this band and her #LightSourceSelfie ends with a fantastic clip of them in action. You can find out more about music at PSI here: Music at PSI | Our Research | Paul Scherrer Institut (PSI)

X-rays look at nuclear fuel cladding with new detail

Micro-beam measurements at the Swiss Light Source SLS have enabled insights into the crystal structure of hydrides that promote cracks in nuclear fuel cladding. This fundamental knowledge of the material properties of cladding will help assess safety during storage.

For over seventy years, zirconium alloys have been used as cladding for nuclear fuel rods. This cladding provides a structural support for the nuclear fuel pellets and an initial barrier to stop fission products escaping into the reactor water during operation. During its long history, which includes extensive research and development advances, reactor type zirconium alloys have proved themselves as an extremely successful material for this application.

Yet they have a well-known nemesis: hydrogen. When submerged in water during operation in a reactor, at the hot surface of the fuel rod water molecules split into hydrogen and oxygen. Some of this hydrogen then diffuses into the cladding. It makes its way through the cladding until – when the concentration and conditions are right – it precipitates to form chemical compounds known as zirconium-hydrides. These hydrides make the material brittle and prone to cracking. Now, using the Swiss Light Source SLS, researchers were able to shed new light on the interplay between cracking and hydride formation.

Using a technique called synchrotron micro-beam X-ray diffraction, the researchers could study the structure of hydrides during the growth of cracks in fuel cladding at a new level of detail. “Through thermomechanical tests, we could control extremely slow crack propagations. Discovering at such high spatial resolution which hydride formations actually occurred made all the challenges of the material preparation worthwhile,” says study first author, Aaron Colldeweih who designed the thermomechanical testing procedure as part of his PhD project at PSI.

One of the things they discovered was that an unexpected type of hydride was present at the crack tip. This type of hydride, known as gamma-hydride has a slightly different crystal structure and stoichiometry to the type more commonly present, known as delta-hydride, “There has been a lot of discussion about gamma-hydrides: whether they are stable and whether they exist at all. Here we could show that with certain applied stresses you create gamma-hydrides that are stable,” says Johannes Bertsch, who leads the Nuclear Fuels Group in the Laboratory of Nuclear Materials at PSI.

Read more on the PSI website

Image: Malgorzata Makowska, scientist at the MicroXAS beamline of the SLS, carefully positions a standard material for setup calibration on the sample manipulator in front of the X-ray beam.

Credit: Paul Scherrer Institute / Mahir Dzambegovic

Laura Heyderman elected Royal Society Fellow

Today, the announcement was made that Laura Heyderman, who leads the Mesoscopic Systems Group at PSI, has been elected Fellow of the Royal Society (FRS). Laura’s nomination recognises almost 30 years of research into magnetic materials and magnetism on the nanoscale, most notably, in the field of artificial spin ice.

Laura Heyderman is best known for her breakthroughs with nanomagnets – minute bar magnets that are a few hundreds of times smaller than the width of a human hair. Her research group, shared between Paul Scherrer Institute PSI and ETH Zurich where she became full professor in 2013, use these to create elaborate structures and devices. With the help of the large research infrastructures at PSI (X-rays, muons and neutrons) they then investigate the novel phenomena that they exhibit. The tiny magnetic systems they create can have a range of technological applications, such as for computation, communication, sensors or actuators.

Read more on the PSI website

Image: Laura Heyderman began working on magnetism as a PhD student investigating magnetic thin films in Paris in 1988. Today, she leads the Mesoscopic Systems Group, shared between PSI and ETH where she is a full professor.

Credit: ETH Zurich / Giulia Marthaler

Cement hydration in 4D: towards a reduction in emissions

Researchers led by the University of Málaga show the Portland cement early age hydration with microscopic detail and high contrast between the components. This knowledge may contribute to more environmentally friendly cements. The results are now published in Nature Communications.

Concrete is a fluid mass that strikingly sets and hardens in hours, even under water. This fabricated rock, which is made of cement, water, sand and gravel, is the basic building block of our civilization. Hence, it is not a surprise that it is the world’s largest manufactured commodity. The enormous production of Portland cement (PC), at 4 billion tonnes per year, results in 2.7 billion tonnes of CO2 emissions per year. If cement production were considered a country, it would be the third CO2 emitter in the world, just after China and USA. Therefore, reducing the CO2 footprint of cement, mortar and concrete is a societal need.

The main drawback of the current proposals for low-carbon cements is the slow hydration kinetics in the first 3 days. “Understanding the processes related to cement hydration as it takes place at its early stages is crucial”, explains Shiva Shirani, first author of the paper and PhD student at the University of Malaga. Despite a century of research, our understanding of cement dissolution and precipitation processes at early ages is very limited. “So we have developed a methodology to get a full picture of the hydration of Portland cement”, she adds.

The team, which is led by the University of Málaga and includes the ESRF, the Paul Scherrer Institute PSI (Switzerland) and the University Grenoble Alpes (France), carried out a tomographic study in the laboratory for an initial characterisation, followed by phase-contrast microtomography experiments with synchrotron radiation to take data very quickly and in large sample volumes, and finally experiments at the nanometric scale, using synchrotron ptychotomography.

Read more on the ESRF website

Image: Scientists followed the hydration process of cement in its early stages

Credit: Shiva Shirani

Always on the pulse of time

On 1 January 2023, the Paul Scherrer Institute PSI turned 35. And these past 35 years have been very eventful. Some of those events have to do with the development and the history of the Institute: new large research facilities have been added; proton therapy has become increasingly important; the spin-offs created at PSI and the licensing agreements concluded were also important. Most recently, the focus has been on exploring quantum physics and using it in practical applications. Another group of events has to do with research itself, with the history of science at PSI. These are about research and research results that are not only, but to a large extent, related to the unique large research facilities available at PSI.

Read more on the PSI website

Image: 1988: Foundation of the Paul Scherrer Institute PSI

X-rays make 3D metal printing more predictable

Insights into the microscopic details of 3D printing gained using the microXAS beamline of the Swiss Light Source SLS could propel the technology toward wider application.

Researchers have not yet gotten the additive manufacturing, or 3D printing, of metals down to a science completely. Gaps in our understanding of what happens within metal during the process have made results inconsistent. But new research could grant a greater level of mastery over metal 3D printing.

Using powerful x-rays generated by the Swiss Light Source SLS and Argonne National Laboratory’s Advanced Photon Source, researchers at Paul Scherrer Institute PSI, the National Institute of Standards and Technology (NIST), KTH Royal Institute of Technology in Sweden and other institutions have peered into the internal structure of steel as it was melted and then solidified during 3D printing. The findings, published in Acta Materialia, unlock a computational tool for 3D-printing professionals, offering them a greater ability to predict and control the characteristics of printed parts, potentially improving the technology’s consistency and feasibility for large-scale manufacturing. 

“So-called operando measurements with x-rays enable us to capture what is really happening to the microstructure during a rapid process such as printing.” said Steven Van Petegem, senior scientist at PSI, who led the experimental work performed at the SLS using the microXAS beamline.

Read more on the PSI website

Image: Researchers used high-speed X-ray diffraction to identify the crystal structures that form within steel as it is 3D-printed. The angle at which the X-rays exit the metal correspond to types of crystal structures within.

Credit: H. König et al. via Creative Commons (, adapted by N. Hanacek/NIST

How football-shaped molecules occur in the universe

For a long time it has been suspected that fullerene and its derivatives could form naturally in the universe. These are large carbon molecules shaped like a football, salad bowl or nanotube. An international team of researchers using the Swiss SLS synchrotron light source at PSI has shown how this reaction works. The results have just been published in the journal Nature Communications.

“We are stardust, we are golden. We are billion-year-old carbon.” In the song they performed at Woodstock, the US group Crosby, Stills, Nash & Young summarised what humans are essentially made of: star dust. Anyone with a little knowledge of astronomy can confirm the words of the cult American band – both the planets and we humans are actually made up of dust from burnt-out supernovae and carbon compounds billions of years old. The universe is a giant reactor and understanding these reactions means understanding the origins and development of the universe – and where humans come from.

In the past, the formation of fullerenes and their derivatives in the universe has been a puzzle. These carbon molecules, in the shape of a football, bowl or small tube, were first created in the laboratory in the 1980s. In 2010 the infrared space telescope Spitzer discovered the C60 molecules with the characteristic shape of a soccer ball, known as buckyballs, in the planetary nebula Tc 1. They are therefore the biggest molecules to have been discovered to date known to exist in the universe beyond our solar system.

But how do they actually form there? A team of researchers from Honolulu (USA), Miami (USA) and Tianjin (China) has now completed an important reaction step in the formation of the molecules, with active support from PSI and the vacuum ultraviolet (VUV) beamline of the synchrotron light source Swiss SLS. “PSI offers unique experimental facilities and that’s why we decided to collaborate with Patrick Hemberger at PSI,” says Ralf Kaiser from the University of Hawaii in Honolulu, the leading international researcher in this field.

Read more on the PSI website

Credit: Shane Goettl/Ralf I. Kaiser

Using light to switch drugs on and off

Scientists at the Paul Scherrer Institute PSI have used the Swiss X-ray free-electron laser SwissFEL and the Swiss Light Source SLS to make a film that could give a decisive boost to developing a new type of drug. They made the advance in the field of so-called photopharmacology, a discipline that develops active substances which can be specifically activated or deactivated with the help of light. The study is being published today in the journal Nature Communications.

Photopharmacology is a new field of medicine that is predicted to have a great future. It could help to treat diseases such as cancer even more effectively than before. Photopharmacological drugs are fitted with a molecular photoswitch. The substance is activated by a pulse of light, but only once it has reached the region of the body where it is meant to act. And after it has done its job, it can be switched off again by another pulse of light.

This could limit potential side effects and reduce the development of drug resistance – to antibiotics, for example.

Licht-switchable drugs

To make conventional drugs sensitive to light, a switch is built into them. In their study, the scientists led by the principal authors Maximilian Wranik and Jörg Standfuss used the active molecule combretastatin A-4, which is currently being tested in clinical trials as an anti-cancer drug. It binds to a protein called tubulin, which forms the microtubules that make up the basic structure of the cells in the body, and also drive cell division. Combretastatin A-4, or “CA4” for short, destabilises these microtubules, thereby curbing the uncontrolled division of cancer cells, i.e. it slows down the growth of tumours.

In the modified CA4 molecule, a bridge consisting of two nitrogen atoms is added, which makes it particularly photoactive. In the inactive state, the so-called azo bridge stretches the molecular components to which it is attached to form an elongated chain. The pulse of light bends the bond, bringing the ends of the chain closer together – like a muscle contracting to bend a joint. Crucially, in its elongated form, the molecule does not fit inside the binding pockets of the tubulin – depressions on the surface of the protein where the molecule can dock in order to exert its effect. However, when the molecule is bent, it fits perfectly – like a key in a lock. Molecules like this, which fit into corresponding binding pockets, are also called ligands.

Read more on the PSI website

Image: Jörg Standfuss (left) and Maximilian Wranik in front of the experimental station Alvra of the Swiss X-ray free-electron laser SwissFEL, where the photopharmacological studies were carried out. In the long term, the aim is to develop drugs that can be switched on and off by light.

Credit: Paul Scherrer Institute/Markus Fischer

A star is born

Swiss Light Source SLS reveals complex chemistry inside ‘stellar nurseries’

An international team of researchers has uncovered what might be a critical step in the chemical evolution of molecules in cosmic “stellar nurseries.” In these vast clouds of cold gas and dust in space, trillions of molecules swirl together over millions of years. The collapse of these interstellar clouds eventually gives rise to young stars and planets.

Like human bodies, stellar nurseries contain a lot of organic molecules, which are made up mostly of carbon and hydrogen atoms. The group’s results, published in the journal Nature Astronomy, reveal how certain large organic molecules may form inside these clouds. It’s one tiny step in the eons-long chemical journey that carbon atoms undergo—forming in the hearts of dying stars, then becoming part of planets, living organisms on Earth and perhaps beyond.

“In these cold molecular clouds, you’re creating the first building blocks that will, in the end, form stars and planets,” said Jordy Bouwman, research associate at the Laboratory for Atmospheric and Space Physics (LASP) and assistant professor in the Department of Chemistry at University Colorado Boulder.

For the new study, Bouwman and his colleagues took a deep dive into one stellar nursery in particular: the Taurus Molecular Cloud (TMC-1). This region sits in the constellation Taurus and is roughly 440 light years (more than 2 quadrillion miles) from Earth. The chemically complex environment is an example of what astronomers call an “accreting starless core.” Its cloud has begun to collapse, but scientists haven’t yet detected embryonic stars emerging inside it.

Read more on the PSI website

Image: Using PEPICO spectroscopy at the SLS, researchers discovered how hexagonally-shaped ortho-benzyne molecules can combine with methyl radicals to form a series of larger organic molecules, each containing a ring of five carbon atoms.

Credit: Henry Cardwell

#SynchroLightAt75 – Grating interferometry and phase-contrast imaging

The development of X-ray phase-contrast imaging at Paul Scherrer Institute PSI tells a story of how basic research can quickly lead to practical applications. Grating interferometry was pioneered by PSI scientists as a technique for characterizing the X-ray wave front at synchrotron sources, such as the Swiss Light Source SLS. This development enhanced the quality of X-ray images. Soon after, it began to be used for phase-contrast imaging of soft matter-like tissue, and was subsequently brought to X-ray lab sources as well. Currently, it is under development for mammography with improved contrast for soft tissue and the micro-calcifications that are markers for benign and malignant tissue alterations.

Read more about this development via these links: Phase contrast improves mammography and Phase-contrast X-ray imaging for advanced breast cancer detection

Image: Marco Stampanoni pioneered the technique of phase-contrast X-ray imaging, which enables higher resolution mammograms that can help detect breast cancer earlier

Credit: Paul Scherrer Institute / Markus Fischer

#SyncroLightAt75 – Structure of the Ribosome

Along with Ada Yonath and Thomas Steitz,Venkatraman Ramakrishnan from the MRC Laboratory of Molecular Biology in Cambridge, UK was awarded the 2009 Nobel Prize in Chemistry for determining the structure of the ribosome, one of the largest and most important molecules in the cell. X-ray crystallography experiments that enabled elucidation of the ribosome structure used synchrotron light from a number of light sources worldwide, each with unique capabilities, including the Swiss Light Source SLS.

Read more on the PSI website

Image: Interior view of the experimental hall at the Swiss Light Source SLS

Credit: Photo: H.R. Bramaz/PSI

Nanomaterial from the Middle Ages

To gild sculptures in the late Middle Ages, artists often applied ultra-thin gold foil supported by a silver base layer. For the first time, scientists at the Paul Scherrer Institute PSI have managed to produce nanoscale 3D images of this material, known as Zwischgold. The pictures show this was a highly sophisticated mediaeval production technique and demonstrate why restoring such precious gilded artefacts is so difficult.

The samples examined at the Swiss Light Source SLS using one of the most advanced microscopy methods were unusual even for the highly experienced PSI team: minute samples of materials taken from an altar and wooden statues originating from the fifteenth century. The altar is thought to have been made around 1420 in Southern Germany and stood for a long time in a mountain chapel on Alp Leiggern in the Swiss canton of Valais. Today it is on display at the Swiss National Museum (Landesmuseum Zürich). In the middle you can see Mary cradling Baby Jesus. The material sample was taken from a fold in the Virgin Mary’s robe. The tiny samples from the other two mediaeval structures were supplied by Basel Historical Museum.

The material was used to gild the sacred figures. It is not actually gold leaf, but a special double-sided foil of gold and silver where the gold can be ultra-thin because it is supported by the silver base. This material, known as Zwischgold (part-gold) was significantly cheaper than using pure gold leaf. “Although Zwischgold was frequently used in the Middle Ages, very little was known about this material up to now,” says PSI physicist Benjamin Watts: “So we wanted to investigate the samples using 3D technology which can visualise extremely fine details.” Although other microscopy techniques had been used previously to examine Zwischgold, they only provided a 2D cross-section through the material. In other words, it was only possible to view the surface of the cut segment, rather than looking inside the material.  The scientists were also worried that cutting through it may have changed the structure of the sample. The advanced microscopy imaging method used today, ptychographic tomography, provides a 3D image of Zwischgold’s exact composition for the first time.

Read more on the PSI website

Image: The altar examined is thought to have been made around 1420 in Southern Germany and for a long time stood in a mountain chapel on Alp Leiggern in the Swiss canton of Valais. Today it is on display at the Swiss National Museum (Landesmuseum Zürich).

Credit: Swiss National Museum, Landesmuseum Zürich