Determination of interatomic coupling between two-dimensional crystals –

using angle-resolved photoemission spectroscopy. Following the isolation of graphene, many other atomically thin two-dimensional crystals have been produced and can even be stacked on top of each other in a desired order to form so called van der Waals heterostructures.

Subtle changes in the stacking, especially the angle between the crystallographic axes of two adjacent layers, can have big impact on the properties of the whole heterostructure. We use angle-resolved photoemission spectroscopy measurements carried out at the Spectromicroscopy beamline at Elettra to obtain interatomic coupling for carbon atoms by studying a three-layer stack of graphene. The coupling between atoms in two two-dimensional crystals, knowledge of which is necessary to describe the properties of the stack, can be determined by studying a structure made of three layers with two similar interfaces but one with crystallographic axes aligned and one twisted. This is because each of the interfaces provides complementary information and together they enable self-consistent determination of the coupling.

Read more on the Elettra website

Image: Angle resolved photoemission spectrum revealing the electronic bands of a microscopic three layer device having aligned and twisted graphene-graphene interfaces. Measurable band gaps are used to self-consistently determine fundamental parameters of interatomic coupling.

Human waste could help combat global food insecurity

Researchers from Cornell University’s College of Agriculture and Life Sciences and the Canadian Light Source (CLS) at the University of Saskatchewan have proven it is possible to create nitrogen-rich fertilizer by combining the solid and liquid components of human waste. The discovery, published recently in the journal Sustainable Chemistry and Engineering, has the potential to increase agriculture yields in developing countries and reduce contamination of groundwater caused by nitrogen runoff. 

Special separating toilets that were developed through the Reinvent the Toilet Challenge have helped solve long-standing sanitation problems in the slums of Nairobi, Kenya. However, the methods used to dispose of the two outputs failed to capture a key nutrient that local fields were starving for: nitrogen.

Cornell researchers Leilah Krounbi, a former PhD student, now at the Weizmann Institute in Israel, and Johannes Lehmann, senior author and professor of soil and crop sciences, wondered whether it might be possible to close the waste stream loop by recycling nitrogen from the urine, which was otherwise being lost to runoff.  While other researchers have engineered adsorbers using high-tech ingredients such as carbon nanotubes or activated carbons, Lehmann and his team wanted to know if they could do so with decidedly low-tech materials like human feces. Adsorbers are materials whose surfaces can capture and hold gas or liquids.

Read more on the Canadian Light Source website

Image: The researchers used the SGM beamline at the CLS to see how the chemistry in the nitrogen changed as it adsorbed ammonia and how well their material could make nitrogen available to plants if it was used as a fertilizer.  

A closer look at superconductors

A new measuring method helps understand the physics of high-temperature superconductivity

From sustainable energy to quantum computers: high-temperature superconductors have the potential to revolutionize today’s technologies. Despite intensive research, however, we still lack the necessary basic understanding to develop these complex materials for widespread application. “Higgs spectroscopy” could bring about a watershed as it reveals the dynamics of paired electrons in superconductors. An international research consortium centered around the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Max Planck Institute for Solid State Research (MPI-FKF) is now presenting the new measuring method in the journal Nature Communications (DOI: 10.1038/s41467-020-15613-1). Remarkably, the dynamics also reveal typical precursors of superconductivity even above the critical temperature at which the materials investigated attain superconductivity.

Read more on the TELBE at HZDR website

Image: Deciphering previously invisible dynamics in superconductors – Higgs spectroscopy could make this possible: Using cuprates, a high-temperature superconductor, as an example, an international team of researchers has been able to demonstrate the potential of the new measurement method. By applying a strong terahertz pulse (frequency ω), they stimulated and continuously maintained Higgs oscillations in the material (2ω). Driving the system resonant to the Eigenfrequency of the Higgs oscillations in turn leads to the generation of characteristic terahertz light with tripled frequency (3ω).

Significant progress on ultraflexible solar cells

Research from Monash University, the University of Tokyo and RIKEN, partly undertaken at the Australian Synchrotron, has produced an ultra-flexible ultra-thin organic solar cell that delivered a world-leading performance under significant stretching and strain.

The development paves the way forward for a new class of stretchable and bendable solar cells in wearable devices, such as fitness and health trackers, and smart watches with complex curved surfaces.

The advance, which was published in Joule, was made possible by designing an ultra-thin material based on a blend of polymer, fullerene and non-fullerene molecules with the desired mechanical properties and power efficiency, according to Dr Wenchao Huang, a Research Fellow at Monash University and the article’s first author.
The thickness of the solar cell film is only three micrometres, which is ten times smaller than the width of a human hair.

Dr Huang, who completed his PhD in the lab of Prof Chris McNeill at Monash on flexible organic solar cells, received the Australian Synchrotron’s Stephen Wilkins Medal in 2016 for his exceptional doctoral thesis that made use of the synchrotron-based research capabilities at the facility.

>Read more no the Autralian Lightsource at ANSTO website

Image: Schematic of ultraflexible solar cell

Beyond graphene: monolayer arsenene observed for the first time

An article recently published in 2D Materials shows the first experimental evidence of the successful formation of arsenene, an analogue of graphene with noteworthy semiconducting properties.

This material shows a great potential for the development of new nanoelectronics. Crucial sample preparation and electron spectroscopy experiments were performed at the Bloch beamline at MAX IV.

The discovery of graphene, the single-layer carbon honeycomb material worth the Nobel Prize in Physics in 2010, surely has had a revolutionary impact on research. It triggered a whole new field of study within two-dimensional (2D) materials. However, its application in developing new 2D electronics has been hindered by its lack on an intrinsic band gap. Researchers therefore started to turn their attention to other elements in the periodic table and set their eyes on group V, to which arsenic belongs.
“The aim of the study was to show that arsenene can be formed. Our article is the first to report this”, says Roger Uhrberg, professor at Linköping University and spokesperson for the Bloch beamline at MAX IV. Arsenene, a single-layer buckled honeycomb structure of arsenic, had been previously predicted by various theoretical studies, but this is the first experimental observation that verifies its existence.

>Read more on the MAX IV website

Image: A view of the Bloch beamline at MAX IV. The Bloch beamline consists of two branchlines, and is dedicated to high resolution photoelectron spectroscopy, encompassing angle-resolved (ARPES), spin resolved (spin-ARPES) and core-level spectroscopy.

Learning how breast cancer cells evade the immune system

Cancer cells have ways to evade the human immune system, but research at UK’s Synchrotron, Diamond could leave them with nowhere to hide.

Announced on World Cancer Day, the latest research (published in Frontiers in Immunology) by Dr Vadim Sumbayev, together with an international team of researchers, working in collaboration with Dr Rohanah Hussain and Prof Giuliano Siligardi at Diamond Light Source.  They have been investigating the complex defence mechanisms of the human immune system and how cancer cells in breast tumours avoid it. In particular, they sought to understand one of the biochemical pathways leading to production of a protein called galectin-9, which cancer cells use to avoid immune surveillance. Dr Vadim Sumbayev explains, The human immune system has cells that can attack invading pathogens, protecting us from bacteria and viruses. These cells are also capable of killing cancer cells, but they don’t. Cancer cells have evolved defence mechanisms that protect them from our immune system, allowing them to survive and replicate, growing into tumours that may then spread across the body. Unfortunately, the molecular mechanisms that allow cancer cells to escape host immune surveillance remain poorly understood.  So, with a growing body of evidence suggesting that some solid tumours also use proteins called Tim-3 and galectin-9 and to evade host immune attack, we chose to study the activity of this pathway in breast and other solid and liquid tumours. 

>Read more on the Diamond Light Source website

Image: Breast cancer cell-based pathobiochemical pathways showing LPHN-induced activation of PKCα, which triggers the translocation of Tim-3 and galectin-9 onto the cell surface which is required for immune escape.

Watching complex molecules at work

A new method of infrared spectroscopy developed at BESSY II makes single-measurement observation and analysis of very fast as well as irreversible reaction mechanisms in molecules feasible for the first time.

Previously, thousands of such reactions have had to be run and measured for this purpose. The research team has now used the new device to investigate how rhodopsin molecules change after activation by light – a process that is the basis of how we see.

Time-resolved infrared spectroscopy in the sub-millisecond range is an important method for studying the relationship between function and structure in biological molecules. However, the method only works if the reaction can be repeated many thousands of times. This is not the case for a large number of biological processes, though, because they often are based on very rapid and irreversible reactions, for example in vision. Individual light quanta entering the rods of the retina activate the rhodopsin protein molecules, which then decay after fulfilling their phototransductionfunction.

>Read more on the BESSY II at HZB website

Image: Rhodopsin before (left) and after activation by light (right): The activation causes changes in functional groups inside the molecule (magnifying glass), which affect the entire molecule.
Credit: E. Ritter/HZB

Multimodal study of ion-conducting membranes

Using multiple x-ray characterization tools, researchers showed how chemical and structural changes improve the performance of a novel ion-conducting polymer (ionomer) membrane from 3M Company.

In fuel cells (which generate clean power from hydrogen fuel) and electrolyzers (water-splitting devices that produce hydrogen fuel), positive and negative electrodes are separated by membranes composed of ion-conducting polymers (ionomers). These membranes prevent contact between the electrodes—thus avoiding catastrophic failure—while allowing selective passage of ions to complete the circuit.

Generally, such membranes are based on a class of perfluorosulfonic acid (PFSA) ionomers with remarkable proton conductivity and stability. Recently, however, companies such as 3M have been developing new ionomers with improved performance. In this work, researchers took a closer look at the structural and chemical properties of these materials at the nanometer scale. The resulting insights provide valuable guidance on design strategies for optimally performing ionomers.

>Read more on the Advanced Light Source website

Image: Resonant x-ray scattering (RXS) and x-ray absorption spectroscopy (XAS) with elemental sensitivity unravel structural features and chemical factors affecting morphology and ion transport in proton-conducting membranes.

First delivery of single-bunch electron beam to the 1.5 GeV ring

The 22 October at lunchtime, the first single-bunch electron beam was delivered to the 1.5 GeV storage ring at MAX IV and put to use at the FinEstBeAMS beamline.

These are still preliminary trials and the response from FinEstBeAMS will determine the path forward.

Normally the electrons in the storage rings come in so-called multi-bunch formation. You could think of this as several locomotives with many wagons travelling around the ring. In single-bunch mode, there is only one locomotive “on the track”. The abstract of Christian Strålman’s PhD thesis On the Challenges for Time-of-Flight Electron Spectroscopy at Storage Rings gives a good overview of the topic in Swedish.

The single-bunch mode will give the scientists access to a wider portfolio of measurement techniques in several research areas such as atmospheric chemistry, environmental science (in particular renewable energy sources), molecular reaction dynamics, cluster chemistry and physics, materials science, chemistry–chemical reactions at surfaces or in solution and photocatalysis.

>Read more on the MAX IV website

Image (extract):A screenshot of a scope measurement of the current in the ring, where you can clearly see the strong single-bunch signal. See full image here.

Synergistic Co−Mn oxide catalyst for oxygen reduction reactions

Researchers employed synchrotron-based X-ray absorption spectroscopy (XAS) at CHESS to investigate the synergistic interaction of bimetallic Co1.5Mn1.5O4/C catalysts… under real-time operando electrochemical conditions.

Identifying the catalytically active site(s) in the oxygen reduction reaction (ORR) is critical to the development of fuel cells and other technologies. Researchers employed synchrotron-based X-ray absorption spectroscopy (XAS) at CHESS to investigate the synergistic interaction of bimetallic Co1.5Mn1.5O4/C catalysts – which exhibit impressive ORR activity in alkaline fuel cells – under real-time operando electrochemical conditions. Under steady state conditions, both Mn and Co valences decreased at lower potentials, indicating the conversion from Mn-(III,IV) and Co(III) to Mn(II,III) and Co(II), respectively. Changes in the Co and Mn valence states are simultaneous and exhibited periodic patterns that tracked the cyclic potential sweeps.

>Read more on the CHESS website

Image: Schematic of the in situ XAS electrochemical cell. Working electrode (WE, catalyst on carbon paper) and counter electrode (CE, carbon rod) were immersed in 1 M KOH solution. The reference electrode was connected to the cell by a salt bridge to minimize IR drops caused by the resistance in the thin electrolyte layer within the X-ray window.

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

Unraveling plants resistance to drought

Research investigates the chemical nanostructure of water conducting vessels.

Plant cells are encased in a structure called the cell wall, composed mainly of cellulose and lignin. Among other functions, this wall gives structural stability to the cells and controls the entry of water, minerals and other substances. When they die, the cells leave behind their cell wall, forming different structures that support the plant giving rigidity to the stems and that facilitate the transport of substances from the roots to the leaves and vice versa. One such structure is the xylem: a continuous network of conduits about 100 micrometers in diameter that carries the water absorbed by the roots to the leaves.

When they lose water by transpiration, the leaves generate tension in the water column within the xylem. The pressure difference between the interior and exterior of the conduit causes the molecules to behave as links in a current: when a molecule of water evaporates, the rest of the “current” is pulled up.

>Read more on the Brazilian Synchrotron Light Laboratory at CNPEM website

Image: Schematic figure of the technique of infrared nanospectroscopy.

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.

HIPPIE provides a closer look at water filtration

Clean fresh water is a scarce resource. Areas of the world suffering from drought have to filter the salt out of seawater to make it drinkable. In other areas, the water may instead have a high content of toxic compounds, such as arsenic.
If you think about a water filter as a kind of strainer with tiny holes through it, you would assume that since it does a pretty good job of filtering out the small ions of normal table salt, sodium, and chloride, from seawater it would work even better for the larger arsenic compounds. This is however not the case when it comes to desalination – the technology for producing fresh water from seawater; quite the opposite actually. While sodium and chloride are removed effectively, other, much larger contaminants pass through the filtration materials that are typically used. That indicates there must be another mechanism at work here.

>Read more on the MAX IV Laboratory website

The best topological conductor yet: spiraling crystal is the key to exotic discovery

X-ray research at Berkeley Lab reveals samples are a new state of matter

The realization of so-called topological materials – which exhibit exotic, defect-resistant properties and are expected to have applications in electronics, optics, quantum computing, and other fields – has opened up a new realm in materials discovery.
Several of the hotly studied topological materials to date are known as topological insulators. Their surfaces are expected to conduct electricity with very little resistance, somewhat akin to superconductors but without the need for incredibly chilly temperatures, while their interiors – the so-called “bulk” of the material – do not conduct current.
Now, a team of researchers working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has discovered the strongest topological conductor yet, in the form of thin crystal samples that have a spiral-staircase structure. The team’s study of crystals, dubbed topological chiral crystals, is reported in the March 20 edition of the journal Nature.

>Read more on the ALS at Berkeley Lab website

Image: This illustration shows a repeated 2D patterning of a property related to electrical conductivity, known as the surface Fermi arc, in rhodium-silicon crystal samples.
Credit: Hasan Lab/Princeton University

Towards X-ray transient grating spectroscopy at SwissFEL

The high brilliance of new X-ray sources such as X-ray Free Electron Laser opens the way to non-linear spectroscopies.

These techniques can probe ultrafast matter dynamics that would otherwise be inaccessible. One of these techniques, Transient Grating, involves the creation of a transient excitation grating by crossing X-ray beams on the sample. Scientists at PSI have realized a demonstration of such crossing by using an innovative approach well suited for the hard X-ray regime. The results of their work at the Swiss Free Electron Laser have been published in the journal Optics Letters.
Non-linear optics is an important field of physics where the non-linear response of matter in extreme electromagnetic fields is studied and exploited for novel applications. It has been widely used for creating new laser wavelengths (Sum/Difference Frequency Generation – S/DFG) as well as for studying a variety of properties such as charge, spin, magnetic transfer as well as heat diffusion. A broad class of non-linear spectroscopy is Four Wave Mixing (FWM) where three laser beams are overlapped in space and time in a sample and a fourth beam with different wavelength and angle is detected, background free. This allows studying specific transitions and selectively excite the sample tuning the incoming beams’ wavelength while studying their dynamics by controlling the relative time delays between the laser pulses. Transient Grating (TG) spectroscopy is a special case of degenerate FWM where two of the incoming beams have the same wavelength and are crossed at the sample creating an interference pattern, or transient grating, which excites the sample as long as the field is present. When the TG impinges on the material, its index of refraction is locally perturbed and electrons exposed to the radiation are excited. These electrons then transfer their extra energy to the lattice and the heat is then dissipated by the system. A third beam, delayed with respect to the pump TG, probes the dynamics of this excitation.

>Read more on the SwissFEL at PSI website

Image: Layout depicting the experimental conditions at the Alvra experimental station. (Find all the details here)