Nanometre gaps can crystallise liquids

X-ray examination shows surprising coexistence of liquid and crystalline form.

Very narrow gaps make liquids crystallise partially. X-ray investigations at DESY show that in gaps just a few molecule diameters wide both, liquid and crystal properties of a material can exist at the same time. The observation of this coexistence is important for all liquids in very small cavities and thus also for the study of friction (tribology). The team led by DESY researchers Milena Lippmann and Oliver Seeck presents the research in The Journal of Physical Chemistry Letters.
It was already known that liquids form atomically thin layers at an interface, such as the bottom or wall of a vessel. At the interface, the liquid is therefore not as disordered as in the volume. A relatively well-ordered layer of molecules of the liquid forms directly on the wall, on top of which a further layer is formed that is somewhat less orderly, on top of which a layer is even less orderly, until after about four to five layers the liquid is disordered.
“Despite this layering, the liquid remains liquid – the chemistry and physics of the layer do not change fundamentally,” explains Seeck. “An interesting situation arises if two smooth interfaces are brought together to a nanometre distance with a liquid between them.” One nanometre is one millionth of a millimetre. This brings the distance into the realm of molecule sizes. Depending on the specific liquid, its molecules can have a diameter of half a nanometre, for example.

>Read more on the PETRA III at DESY website

Image: Experimental set-up: In a diamond anvil cell, liquid is confined to a few nanometres narrow gap (centre). In this environment, layers and crystallisation coexist, as the X-ray investigation has shown.
Credit: DESY, Milena Lippmann

Exotic properties of iridium compounds

Scientists at DESY’s X-ray source PETRA III and the London Centre for Nanotechnology, at University College London, have developed a new method for examining the astonishing properties of a special class of iridium oxides known as iridates. The team of principal author Pavel Alexeev, from the Dynamics Beamline P01 at PETRA III, is presenting the procedure in the journal Scientific Reports.

Many oxides belonging to certain groups of transition metals (chemical elements with an incomplete d electron shell) are known for their exotic magnetic and electronic properties. These can be attributed qualitatively to a range of interactions between the charge of the electrons, their magnetic moment, their localization within the crystals and their atomic orbitals. The relative strengths of the various interactions determine whether an oxide is magnetic, an insulator, an electrical conductor or even a superconductor. The so-called 4d and 5d transitions metals are particularly interesting in this respect.

The properties of many of these oxides can be specifically adjusted by applying external electric or magnetic fields, or exerting pressure on the material. This makes them interesting for numerous applications in micro- and nanoelectronics, for data storage and information processing. Such behaviour is particularly pronounced in the oxides of 5d transition metals, such as tantalum, tungsten, osmium and iridium. The oxides of iridium are especially remarkable because they lose their magnetisation when subjected to pressure, and even under normal conditions develop unexpected magnetic structures. Although some of their properties have been known for quite a while, efforts to explain this behaviour are still in their infancy. This makes it all the more important to develop methods that provide detailed insights into such materials.

A particularly suitable and extremely sensitive method of studying the electronic and magnetic properties of solids is nuclear resonant scattering (NRS) using synchrotron radiation. This method uses the nuclei of the atoms of certain isotopes as local probes for the material’s properties. In view of its numerous possible applications, specialised measuring stations have been set up for this purpose on the P01 beamline at PETRA III, which are used by many scientists from all over the world every year. Among other things, the method allows the orientation of atomic magnetic moments to be determined with great accuracy. NRS therefore complements other X-ray techniques and – in contrast to neutron techniques – makes it possible to study small samples, for example when used on samples subject to high pressure.

>Read more on the PETRA III at DESY website

Image: Samples of strontium-iridium-trioxid crystals.
Credit: University College London, James Vale/Emily Hunter

New method for imaging electronic orbitals in solids

Orbital states are quantum mechanical constructions that describe the probability to find an electron in an atom, molecule or solid.  We know from atomic physics that an s-orbital is spherical or that a p-orbital is dumbbell-shaped, but how do the complicated distributions of the electrons that contribute to chemical bonds in solids look like?  Knowledge of these orbital states or electron distributions is the basis for our understanding of chemical bonds and related physical properties, which is a crucial step towards tailoring materials with specific characteristics. Here X-ray spectroscopy has contributed tremendously, however, the interpretation of the spectra is not easy and is often based on some assumptions for the analysis of the data.  Hence it would be very important to have an experimental method that gives a direct image of the local electron density.

Image: (a) (b) Integrated intensities of the M1 transition 3s→3d in the Fig. above plotted on the respective projections of the 3A2 3d(x2-y2/3z2-r2) orbital of Ni2+. (c) The three dimensional plot of the 3A2 3d(x2-y2/3z2-r2) orbital (more specific: the hole density) with the projections as in (a) and (b), respectively.
Credit: © MPI CPfS

How virtual photons alter atomic X-ray spectra

Control out of the vacuum, virtually

Certain X-ray optical properties of metal atoms can be controlled with the help of virtual photons. This has been demonstrated for the first time by a DESY research team at PETRA III, by using the highly brilliant radiation from this X-ray light source at DESY. In the journal Physical Review Letters they report on how the X-ray spectra of metal atoms can be controlled by virtual photons. This opens up new possibilities for specifically modifying the X-ray optical properties of materials.
So-called virtual photons play an important role in the interaction of light and matter. This is quite remarkable because they do not exist in the classical sense. Virtual photons are created in the vacuum out of nothing and then disappear again after an extremely short time. If these photons interact during their short existence with the electrons of an atom, the binding energies of the electrons shift ever so slightly.

>Read more on the PETRA III website at DESY

Image: Experimental setup to measure the collective Lamb shift at tantalum.
Credit: DESY, Haber et al.

Scientists develop printable water sensor

X-ray investigation reveals functioning of highly versatile copper-based compound

A new, versatile plastic-composite sensor can detect tiny amounts of water. The 3d printable material, developed by a Spanish-Israeli team of scientists, is cheap, flexible and non-toxic and changes its colour from purple to blue in wet conditions. The researchers lead by Pilar Amo-Ochoa from the Autonomous University of Madrid (UAM) used DESY’s X-ray light source PETRA III to understand the structural changes within the material that are triggered by water and lead to the observed colour change. The development opens the door to the generation of a family of new 3D printable functional materials, as the scientists write in the journal Advanced Functional Materials (early online view).

>Read more on the PETRA III at DESY website

Image: When dried, for example in a water-free solvent, the sensor material turns purple.
Credit: UAM, Verónica García Vegas

Simulating meteorite impacts in the lab

Scientists monitor the response of feldspar minerals to rapid compression

A US-German research team has simulated meteorite impacts in the lab and followed the resulting structural changes in two feldspar minerals with X-rays as they happened. The results of the experiments at DESY and at Argonne National Laboratory in the US show that structural changes can occur at very different pressures, depending on the compression rate. The findings, published in the 1 February issue of the scientific journal Earth and Planetary Science Letters (published online in advance), will aid other scientist to reconstruct the conditions leading to impact craters on Earth and other terrestrial planets.

>Read more on the PETRA III at DESY website

Image: Scanning electron microscopy image of the micro-structure of albite prior to the rapid compression experiments.
Credit: Stony Brook University, Lars Ehm

What keeps spiders on the ceiling?

DESYs X-ray source PETRA III reveals details of adhesive structures of spider legs

Hunting spiders easily climb vertical surfaces or move upside down on the ceiling. A thousand tiny hairs at the ends of their legs make sure they do not fall off. Like the spider’s exoskeleton, these bristle-like hairs (so-called setae) mainly consist of proteins and chitin, which is a polysaccharide. To find out more about their fine structure, an interdisciplinary research team from the Biology and Physics departments at Kiel University and the Helmholtz-Zentrum Geesthacht (HZG) examined the molecular structure of these hairs in closer detail at DESY’s X-ray light source PETRA III and at the European Synchrotron Radiation Facility ESRF. Thanks to the highly energetic X-ray light, the researchers discovered that the chitin molecules of the setae are specifically arranged to withstand the stresses of constant attachment and detachment. Their findings could be the basis for highly resilient future materials. They have been published in the current issue of the Journal of the Royal Society Interface.

>Read more on the PETRA III at DESY website

Image: In order to find out why the hunting spider Cupiennius salei adheres so well to vertical surfaces, the interdisciplinary research team investigates the tiny adhesive hairs on the spider legs.
Credit: Universität Kiel, Julia Siekmann

Platinum forms nano-bubbles

Technologically important noble metal oxidises more readily than expected.

Platinum, a noble metal, is oxidised more quickly than expected under conditions that are technologically relevant. This has emerged from a study jointly conducted by the DESY NanoLab and the Vienna University of Technology. Devices that contain platinum, such as the catalytic converters used to reduce exhaust emissions in cars, can suffer a loss in efficacy as a result of this reaction. The team around principal author Thomas Keller, from DESY and the University of Hamburg, is presenting its findings in the journal Solid State Ionics. The result is also a topic at the users’ meeting of DESY’s X-ray light sources with more than 1000 participants currently taking place in Hamburg.
“Platinum is an extremely important material in technological terms,” says Keller. “The conditions under which platinum undergoes oxidation have not yet been fully established. Examining those conditions is important for a large number of applications.”
The scientists studied a thin layer of platinum which had been applied to an yttria-stabilised zirconia crystal (YSZ crystal), the same combination that is used in the lambda sensor of automotive exhaust emission systems. The YSZ crystal is a so-called ion conductor, meaning that it conducts electrically charged atoms (ions), in this case oxygen ions. The vapour-deposited layer of platinum serves as an electrode. The lambda sensor measures the oxygen content of the exhaust fumes in the car and converts this into an electrical signal which in turn controls the combustion process electronically to minimize toxic exhausts.

>Read more on the DESY (PETRA III) website

Image: Electron microscope view into the interior of a platinum bubble. The cross-section was exposed with a focused ion beam. Below the hollow Pt bubble the angular YSZ crystal can be seen.
Credit: DESY, Satishkumar Kulkarni

LEAPS holds its first plenary meeting

Synchrotron radiation source SESAME welcomed as associated partner

On 12 and 13 November, the League of European Accelerator-based Photon Sources (LEAPS), the association of European research lightsources, met at DESY for its first plenary meeting. More than 150 scientists from the 16 accelerator-based lightsources in Europe, which are members of LEAPS, travelled to Hamburg to do so. Among them were the directors of all institutions, representatives of eight national science ministries and research funding agencies as well as Philippe Froissard from the European Commission.
“The League of European Accelerator-based Photon Sources has made great progress since its foundation a year ago, and I am convinced that this is the way to make our science with European lightsources shine even brighter in the future,” said Helmut Dosch, Chairperson of LEAPS, who opened the meeting together with LEAPS Vice-Chairperson Caterina Biscari from the Spanish synchrotron radiation source ALBA. The LEAPS consortium represents the interests of more than 25 000 users in total.
>Read more on the DESY website
and another article on the ALBA website. Please find here all news about the LEAPS initiative.

X-ray fluorescence imaging could open up new diagnostic possibilities in medicine

Using gold to track down diseases

A high-precision X-ray technique, tested at PETRA III, could catch cancer at an earlier stage and facilitate the development and control of pharmaceutical drugs. The test at DESY’s synchrotron radiation source, which used so-called X-ray fluorescence for that purpose, has proved very promising, as is now being reported in the journal Scientific Reports by a research team headed by Florian Grüner from the University of Hamburg. The technique is said to offer the prospect of carrying out such X-ray studies not only with higher precision than existing methods but also with less of a dose impact. However, before the method can be used in a clinical setting, it still has to undergo numerous stages of development.

The idea behind the procedure is simple: tiny nanoparticles of gold having a diameter of twelve nanometres (millionths of a millimetre) are functionalised with antibodies using biochemical methods. “A solution containing such nanoparticles is injected into the patient,” explains Grüner, a professor of physics at the Centre for Free-Electron Laser Science (CFEL), a cooperative venture between DESY, the University of Hamburg and the Max Planck Society. “The particles migrate through the body, where the antibodies can latch onto a tumour that may be present.” When the corresponding parts of the patient’s body are scanned using a pencil X-ray beam, the gold particles emit characteristic X-ray fluorescence signals, which are recorded by a special detector. The hope is that this will permit the detection of tiny tumours that cannot be found using current methods.

>Read more on the PETRA III at DESY website

Image: Gold nanoparticles spiked with antibodies can specifically attach to tumors or other targets in the organism and can be detected there by X-ray fluorescence.
Credit: Meletios Verras [Source]

Extremely small magnetic nanostructures with invisibility cloak

Future data storage technology

In novel concepts of magnetic data storage, it is intended to send small magnetic bits back and forth in a chip structure, store them densely packed and read them out later. The magnetic stray field generates problems when trying to generate particularly tiny bits. Now, researchers at the Max Born Institute (MBI), the Massachusetts Institute of Technology (MIT) and DESY were able to put an “invisibility cloak” over the magnetic structures. In this fashion, the magnetic stray field can be reduced, allowing for small yet mobile bits. The results were published in Nature Nanotechnology.

For physicists, magnetism is intimately coupled to rotating motion of electrons in atoms. Orbiting around the atomic nucleus as well as around their own axis, electrons generate the magnetic moment of the atom. The magnetic stray field associated with that magnetic moment is the property we know from e.g. a bar magnet we use to fix notes on pinboard. It is also the magnetic stray field that is used to read the information from a magnetic hard disk drive. In today’s hard disks, a single magnetic bit has a size of about 15 x 45 nanometer, about of those would fit on a stamp.

One vision for a novel concept to store data magnetically is to send the magnetic bits back and forth in a memory chip via current pulses, in order to store them at a suitable place in the chip and retrieve them later. Here, the magnetic stray field is a bit of a curse, as it prevents that the bits can be made smaller for even denser packing of the information. On the other hand, the magnetic moment underlying the stray field is required to be able to move the structures around.

>Read more on the PETRA III at DESY website

Credit: MIT, L. Caretta/M. Huang [Source]

X-rays reveal L-shape of scaffolding protein

Structural biologists discover unexpected results at PETRA III at DESY in Germany.

An investigation at DESY’s X-ray light source PETRA III has revealed a surprising shape of an important scaffolding protein for biological cells. The scaffolding protein PDZK1 is comprised of four so-called PDZ domains, three linkers and a C-terminal tail. While bioinformatics tools had suggested that PDZK1’s PDZ domains and linkers would behave like beads on a string moving around in a highly flexible manner, the X-ray experiments showed that PDZK1 has a relatively defined L-shaped conformation with only moderate flexibility. The team led by Christian Löw from the Centre for Structural Systems Biology CSSB at DESY and Dmitri Svergun from the Hamburg branch of the European Molecular Biology Laboratory EMBL report their results in the journal Structure.

Similar to metal scaffolding which provides construction workers with access points to a building, scaffolding proteins mediate interactions between proteins situated on the membrane of the human cell. While the molecular structure of each of PDZK1’s four individual PDZ domains has been solved using X-ray crystallography and NMR spectroscopy, the overall arrangement of the domains in the protein as well as their interactions was not yet understood.

>Read more on the PETRA III at DESY website

Image: Artistic shape interpretation of the scaffolding protein PDZK1. (Credit: Manon Boschard)tistic shape interpretation of the scaffolding protein PDZK1.
Credit: Manon Boschard

Shining a new light on biological cells

Combined X-ray and fluorescence microscope reveals unseen molecular details

A research team from the University of Göttingen has commissioned at the X-ray source PETRA III at DESY a worldwide unique microscope combination to gain novel insights into biological cells. The team led by Tim Salditt and Sarah Köster describes the combined X-ray and optical fluorescence microscope in the journal Nature Communications. To test the performance of the device installed at DESY’s measuring station P10, the scientists investigated heart muscle cells with their new method.

Modern light microscopy provides with ever sharper images important new insights into the interior processes of biological cells, but highest resolution is obtained only for the fraction of biomolecules which emit fluorescence light. For this purpose, small fluorescent markers have to be first attached to the molecules of interest, for example proteins or DNA. The controlled switching of the fluorescent dye in the so-called STED (stimulated emission depletion) microscope then enables highest resolution down to a few billionth of a meter, according to principle of optical switching between on- and off-state introduced by Nobel prize winner Stefan Hell from Göttingen.

>Read more on the PETRA III at DESY website

Image: STED image (left) and X-ray imaging (right) of the same cardiac tissue cell from a rat. For STED, the network of actin filaments in the cell, which is important for the cell’s mechanical properties, have been labeled with a fluorescent dye. Contrast in the X-ray image, on the other hand, is directly related to the total electron density, with contributions of labeled and unlabeled molecules. By having both contrasts at hand, the structure of the cell can be imaged in a more complete manner, with the two imaging modalities “informing each other”.
Credit: University of Göttingen, M. Bernhardt et al.

Google Maps for the cerebellum

A team of researchers from Göttingen has successfully applied a special variant of X-ray imaging to brain tissue. With the combination of high-resolution measurements at DESY’s X-ray light source PETRA III and data from a laboratory X-ray source, Tim Salditt’s group from the Institute of X-ray Physics at the Georg August University of Göttingen was able to visualize about 1.8 million nerve cells in the cerebellar cortex. The researchers describe the investigations with the so-called phase contrast tomography in the Proceedings of the National Academy of Sciences (PNAS).
The human cerebellum contains about 80 percent of all nerve cells in 10 percent of the brain volume – one cubic millimeter can therefore contain more than one million nerve cells. These process signals that mainly control learned and unconscious movement sequences. However, their exact positions and neighbourhood relationships are largely unknown. “Tomography in the so-called phase contrast mode and subsequent automated image processing enables the cells to be located and displayed in their exact position,” explains Mareike Töpperwien from the Institute of X-ray Physics at the University of Göttingen, lead author of the publication.

>Read more on the PETRA III at DESY website

Image: Result of the phase contrast X-ray tomography at DESY’s X-ray source PETRA III.
Credit: Töpperwien et al., Universität Göttingen

Enlightening yellow in art

Scientists from the University of Perugia (Italy), CNR (Italy), University of Antwerp, the ESRF and DESY, have discovered how masterpieces degrade over time in a new study with mock-up paints carried out at synchrotrons ESRF and DESY. Humidity, coupled with light, appear to be the culprits.

The Scream by Munch, Flowers in a blue vase by Van Gogh or Joy of Life by Matisse, all have something in common: their cadmium yellow pigment. Throughout the years, this colour has faded into a whitish tone and, in some instances, crusts of the paint have arisen, as well as changes in the morphological properties of the paint, such as flaking or crumbling. Conservators and researchers have come to the rescue though, and they are currently using synchrotron techniques to study in depth these sulphide pigments and to find a solution to preserve them in the long run.

“This research has allowed us to make some progress. However, it is very difficult for us to pinpoint to what causes the yellow to go white as we don’t have all the information about how or where the paintings have been kept since they were done in the 19th century”, explains Letizia Monico, scientist from the University of Perugia and the CNR-ISTM. Indeed, limited knowledge of the environmental conditions (e.g., humidity, light, temperature…) in which paintings were stored or displayed over extended periods of time and the heterogeneous chemical composition of paint layers (often rendered more complex by later restoration interventions) hamper a thorough understanding of the overall degradation process.

>Read more on the ESRF website

Image: Some of the mock-up paints, prepared by Letizia Monico. Credits: C. Argoud.

Helmholtz Association supports ATHENA

ATHENA (“Accelerator Technology HElmholtz iNfrAstructure”) is a new research and development platform focusing on accelerator technologies and drawing on the resources of all six Helmholtz accelerator institutions (DESY, Jülich Research Centre, Helmholtz Centre Berlin, Helmholtz Centre Dresden-Rossendorf HZDR, KIT and GSI with the Helmholtz Institute of Jena). The Helmholtz Association has now decided to pay almost 30 million euros towards ATHENA as a strategic development project. “This decision demonstrates the Helmholtz Association’s strong commitment to developing and supplying ground-breaking new accelerator technologies for solving the future challenges faced by society,” says Helmut Dosch, who is the Chairman of DESY’s Board of Directors and also the spokesperson for the Helmholtz Association’s research division Matter.

Together, these centres want to set up two German flagship projects in accelerator research based on innovative plasma-based particle accelerators and ultramodern laser technology: an electron accelerator at DESY in Hamburg and a hadron accelerator at HZDR. At both facilities, a range of different fields of application are to be developed, ranging from a compact free-electron laser, through novel medical uses to new applications in nuclear and particle physics. As soon as they have reached the necessary level of maturity to be put to practical use in a particular area, new compact devices could be built for use in other Helmholtz centres, as well as in universities and hospitals.

>Read more on the Bessy II at HZB website or the DESY website