spectroscopy – Page 2 – Lightsources.org

Significant progress on ultraflexible solar cells

2020/04/292020/05/21

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.

Image: Schematic of ultraflexible solar cell

Beyond graphene: monolayer arsenene observed for the first time

2020/02/272020/02/27

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

2020/02/042020/02/20

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.

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

2020/01/142020/01/15

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.

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

2019/10/252019/10/31

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.

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

2019/10/222019/10/24

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

2019/10/092019/10/10

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 Co_1.5Mn_1.5O₄/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

2019/04/022019/04/04

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(x^2-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

2019/03/292019/04/09

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.

Image: Schematic figure of the technique of infrared nanospectroscopy.

How virtual photons alter atomic X-ray spectra

2019/03/292019/04/04

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.

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

HIPPIE provides a closer look at water filtration

2019/03/222019/03/22

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.

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

2019/03/202019/03/22

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.

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

2019/03/012019/04/16

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.

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

Water is more homogeneous than expected

2019/02/202019/02/21

In order to explain the known anomalies in water, some researchers assume that water consists of a mixture of two phases even under ambient conditions.

However, new X-ray spectroscopic analyses at BESSY II, ESRF and Swiss Light Source show that this is not the case. At room temperature and normal pressure, the water molecules form a fluctuating network with an average of 1.74 ± 2.1% donor and acceptor hydrogen bridge bonds per molecule each, allowing tetrahedral coordination between close neighbours.
Water at ambient conditions is the matrix of life and chemistry and behaves anomalously in many of its properties. Since Wilhelm Conrad Röntgen, two distinct separate phases have been argued to coexist in liquid water, competing with the other view of a single-phase liquid in a fluctuating hydrogen bonding network – the continuous distribution model. Over time, X-ray spectroscopic methods have repeatedly been interpreted in support of Röntgen’s postulate.

Image: Water molecules are excited with X-ray light (blue). From the emitted light (purple) information on H-bonds can be obtained.
Credit: T. Splettstoesser/HZB

Single atoms can make more efficient catalysts

2019/01/072019/01/31

Detailed observations of iridium atoms at work could help make catalysts that drive chemical reactions smaller, cheaper and more efficient.

Catalysts are chemical matchmakers: They bring other chemicals close together, increasing the chance that they’ll react with each other and produce something people want, like fuel or fertilizer.

Since some of the best catalyst materials are also quite expensive, like the platinum in a car’s catalytic converter, scientists have been looking for ways to shrink the amount they have to use.

Now scientists have their first direct, detailed look at how a single atom catalyzes a chemical reaction. The reaction is the same one that strips poisonous carbon monoxide out of car exhaust, and individual atoms of iridium did the job up to 25 times more efficiently than the iridium nanoparticles containing 50 to 100 atoms that are used today.

>Read more on the SSRL at SLAC website

Image: Scientists used a combination of four techniques, represented here by four incoming beams, to reveal in unprecedented detail how a single atom of iridium catalyzes a chemical reaction.
Credit: Greg Stewart/SLAC National Accelerator Laboratory

Doped epitaxial graphene close to the Lifshitz transition

2018/11/142018/12/06

Graphene, an sp²bonded sheet of carbon atoms, is still attracting lots of interest almost 15 years after its discovery. Angle-resolved photoemission spectroscopy (ARPES) is a uniquely powerful method to study the electronic structure of graphene and it has been used extensively to study the coupling of electrons to lattice vibrations (phonons) in doped graphene. This electron-phonon coupling (EPC) manifests as a so-called “kink” feature in the electronic band structure probed by ARPES. What is much less explored is the effect of EPC on the phonon structure. A very accurate probe of the phonons in graphene is Raman spectroscopy.
M.G. Hell and colleagues from Germany, Italy, Indonesia, and Japan combined ARPES (carried out at the BaDelPhbeamline – see Figure 1) with low energy electron diffraction (LEED) and Raman spectroscopy (carried out at the University of Cologne in Germany) in a clever way to fully understand the coupled electron-phonon system in alkali metal doped graphene. LEED revealed ordered (1×1), (2×2), and (sqrt3xsqrt3)R30°adsorbate patterns with increasing alkali metal deposition. The ARPES analysis yielded not only the carrier concentration but also the EPC coupling constant. Ultra-High Vacuum (UHV) Raman spectra carried out using identically prepared samples with the very same carrier concentrations provided the EPC induced changes in the phonon frequencies.

Image: Top: ARPES spectra along the Γ-K-M high symmetry direction of the hexagonal Brillouin zone for Cs doped graphene/Ir(111) with increasing Cs deposition. The Dirac energy E_D and the observed LEED reconstruction are also indicated. Bottom: Corresponding Fermi surfaces at the indicated charge carrier concentration.