atoms – Lightsources.org

Direct observation of the ad- and desorption of guest atoms into a mesoporous host

2021/04/212021/04/22

Battery electrodes, storage devices for gases, and some catalyst materials have tiny functional pores that can accommodate atoms, ions, and molecules. How these guest atoms are absorbed into or released from the pores is crucial to understanding the porous materials’ functionality. However, usually these processes can only be observed indirectly. A team from the Helmholtz Zentrum Berlin (HZB) has employed two experimental approaches using the ASAXS instrument at the PTB X-ray beamline of the HZB BESSY II synchrotron to directly observe the adsorption process of atoms in a mesoporous model system. The work lays the foundations for new insights into these kinds of energy materials.

Most battery materials, novel catalysts, and storage materials for hydrogen have one thing in common: they have a structure comprised of tiny pores in the nanometer range. These pores provide space which can be occupied by guest atoms, ions, and molecules. As a consequence, the properties of the guest and the host can change dramatically. Understanding the processes inside the pores is crucial to develop innovative energy technologies.

Read more on the HZB website

Image: From the measurement data, the team was able to determine that the xenon atoms first accumulate on the inner walls of the pores (state 1), before they fill them up (state 2). The X-ray beam penetrates the sample from below.

Credit: © M. Künsting/HZB

Atomic vibrations play key role in material phase change

2020/06/092020/06/10

A research group working with MAX IV’s FemtoMAX beamline has succeeded to slow the phase change from the solid to liquid state in the semiconductor, indium antimonide (InSb), by reducing the inherent vibrations between atoms. An important precursory step in the process was non-thermal melting of the sample, which broke its atomic bonds. This revealed that unbound atoms move with the velocity they had at the instant the bonds were broken. Further it showed that initial velocity is governed by atomic vibrations, which in turn are temperature dependent. The findings are steps toward functional manipulation of material structure during phase transitions.

Imagine a world where we control the structure of materials by subjecting them to short-pulse laser radiation. This is the implication of research that allows us to alter the timing when phase change occurs.

Melting a material with or without heat produces a similar result, at a similar speed. What is going on at the atomic level is quite different, however. Thermal heating excites electrons to a higher energy state. Electron-phonon coupling then equilibrates the electron and lattice temperature which makes the lattice vibrate so violently that atomic bonds break. Non-thermal heating also excites electrons but breaks the bonds instantly—within femtoseconds—and releases atoms from their original structural configuration. Scientists seek to distinguish what happens after bonds sever due to these excited electrons.

Read more on the MAX IV website

Image : FemtoMAX beamline at MAX IV

Beryllium configuration with neighbouring oxygen atoms revealed

2019/06/252019/06/26

High-pressure experiments prove 50-year-old theoretical prediction.

In high-pressure experiments at DESY’s X-ray light source PETRA III, scientists have observed a unique configuration of beryllium for the first time: At pressures nearly a million times the average atmospheric pressure, beryllium in a phosphate crystal acquires six neighbouring atoms instead of the usual four. This six-fold coordination had been predicted by theory more than 50 ago, but could not be observed until now in inorganic compounds. DESY scientist Anna Pakhomova and her collaborators report their results in the journal Nature Communications.
“Originally, chemistry textbooks stated that elements like beryllium from the second period of the periodic table could never have more than four neighbours, due to their electron configuration”, explains Pakhomova. “Then around 50 years ago theorists discovered that higher coordinations could actually be possible, but these have adamantly evaded experimental proof in inorganic compounds.” Inorganic compounds are typically those without carbon – apart from a few exceptions like carbon dioxide and carbon monoxide.

Image: Transformation of the usual fourfold coordination of beryllium to five- and sixfold with increasing pressure. (Credit: DESY, Anna Pakhomova)

New technique for two-dimensional material analysis

2019/03/112019/03/13

Discovery allows scientists to look at how 2D materials move with ultrafast precision.

Using a never-before-seen technique, scientists have found a new way to use some of the world’s most powerful X-rays to uncover how atoms move in a single atomic sheet at ultrafast speeds.

The study, led by researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory and in collaboration with other institutions, including the University of Washington and DOE’s SLAC National Accelerator Laboratory, developed a new technique called ultrafast surface X-ray scattering. This technique revealed the changing structure of an atomically thin two-dimensional crystal after it was excited with an optical laser pulse.
>Read more on the Advanced Photon Source at Argonne website
>Another article is also available on the Linac Coheren Light Source at SLAC website

Image: An experimental station at SLAC’s Linac Coherent Light Source X-ray free-electron laser, where scientists used a new tool they developed to watch atoms move within a single atomic sheet.
Credit: SLAC National Accelerator Laboratory

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

Single atoms break carbon’s strongest bond

2018/10/022018/10/02

Scientists discovered that single atoms of platinum can break the bond between carbon and fluorine, one of the strongest known chemical bonds.

An international team of scientists including researchers at Yale University and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have developed a new catalyst for breaking carbon-fluorine bonds, one of the strongest chemical bonds known. The discovery, published on Sept. 10 in ACS Catalysis, is a breakthrough for efforts in environmental remediation and chemical synthesis.

“We aimed to develop a technology that could degrade polyfluoroalkyl substances (PFAS), one of the most challenging pollutant remediation problems of the present day,” said Jaehong Kim, a professor in the department of chemical and environmental engineering at Yale University. “PFAS are widely detected all over the world, from Arctic biota to the human body, and concentrations in contaminated groundwater significantly exceed the regulatory limit in many areas. Currently, there are no energy-efficient methods to destroy these contaminants. Our collaboration with Brookhaven Lab aims to solve this problem by taking advantage of the unique properties of single atom catalysts.”

Image: Brookhaven scientist Eli Stavitski is shown at NSLS-II’s Inner Shell Spectroscopy beamline, where researchers imaged the physical and chemical complexity of a single-atom catalyst that breaks carbon-fluorine bonds.

Highly efficient single-atom catalyst could help auto industry

2018/09/242018/09/27

A longer-lasting, higher-efficiency platinum catalyst has been developed by a Dalhousie University-led team, a result with major implications for the automobile industry.

Platinum catalysts help deactivate toxic exhaust gases from traditional car engines. Platinum is also used to help drive the chemical reactions that make zero-emissions hydrogen fuel cells possible – a technology that could transform automobiles as we know them.

The new catalyst combines gold and platinum to form what’s known as a single-atom catalyst, resulting in nearly 100-fold increases in efficiency over market platinum catalysts, says Peng Zhang, the Dalhousie professor who led this research.
Not only is efficiency improved at the outset, but it is maintained through the catalyst’s lifetime: normally, a platinum catalyst works less well over time as carbon monoxide molecules tightly bond to and block platinum from helping reactions along.
Improvements come from two properties: the single atom structure, which maximizes platinum’s active surface area, and the unique electronic properties that adding gold to create an alloy helps to achieve.

Image: The blue balls represent platinum atoms, surrounded by gold atoms (yellow). This structure maximizes the platinum catalyst’s efficiency.

The electronic structure of a “Kagome” material

2018/06/152018/07/12

The greater understanding of kagome materials afforded by this work helps open up a new path toward goals such as ultralow-power electronic devices and quantum computing.

In a “kagome” material, the atoms in a layer form a lattice resembling a traditional Japanese basket-weaving pattern (kago means “basket” and me means “eye,” a reference to the large holes characteristic of this open weave). The quasi-hexagonal symmetry is reminiscent of the hexagonal lattice of graphene, a material well known for its unusual electronic properties.

Recent theoretical developments have suggested that, under some conditions, a kagome material could, like graphene, exhibit a wide range of novel physics. In these phenomena, certain electronic excitations (“massive Dirac fermions”) play a major role. Despite predictions, however, the presence of these electronic modes in kagome compounds has evaded direct experimental observation.

Image: Artistic interpretation of kagome crystals.
Images by F. Frankel/MIT; illustration overlays by C. Turner/MIT

New class of single atoms catalysts for carbon nanotubes

2018/04/302018/05/02

They exhibit outstanding electrochemical reduction of CO2 to CO.

Experiments using X-rays on two beamlines at the Australian Synchrotron have helped characterise a new class of single atom catalysts (SACs) supported on carbon nanotubes that exhibit outstanding electrochemical reduction of CO2 to CO. A weight loading of 20 wt% for the new class, nickel single atom nitrogen doped carbon nanotubes (NiSA-N-CNTs), is believed to be the highest metal loading for SACs reported to date.

Single atoms of nickel, cobalt and iron were supported on nitrogen doped carbon nanotubes via a one-pot pyrolysis method and compared in the study.

A large international collaboration, led by Prof San Ping Jiang, Deputy Director of the Fuels and Energy Technology Institute at the Curtin University of Technology and associates from the Department of Chemical Engineering, have developed a new synthesis and development process for nitrogen-doped carbon nanotubes with a nickel ligand that demonstrate high catalytic activity.

The study was published in Advanced Materials and featured on the inside cover of the publication.

Dr Bernt Johannessen, instrument scientist on the X-ray absorption spectroscopy (XAS) beamline at the Australian Synchrotron was a co-author on the paper, which also included lead investigators from Curtin University of Technology and collaborators at the University of Western Australia, Institute of Metal Research (China), Oak Ridge National Laboratory (US), University of the Sunshine Coast, University of Queensland, Tsinghua University (China) and King Abdulaziz University (Saudi Arabia). Technical support and advice on the soft X-ray spectroscopy experiments was provided by Australian Synchrotron instrument scientist Dr Bruce Cowie.

Image: extract of the cover of Advanced Materials.

The Molecular Scale Structure of Electrolyte-Metal Oxide Interface

2018/02/282018/03/08

Li-ion batteries (LIBs) are key components of portable electronic devices, as well as in electric vehicles, military and medical equipment, backup power supplies, and even grid storage. However, the energy storage capacity and rate capability of current LIBs is still too low to meet the increasing demand of key markets. For the latter, the properties of the electrolyte-electrode interface play a decisive role.

From a more general point of view, interfaces, or surfaces, are the outer boundary of any condensed matter. Due to the resulting symmetry breaking, the arrangement of atoms or molecules at the interface often varies significantly from that in the bulk. Studies of the molecular scale structural properties of liquids at interfaces are intriguing, as these give insights into the fundamental molecule–molecule and molecule–substrate interactions. Investigations have included layering of ionic liquids [1], layering of metallic [2] and non-metallic liquids [3], and the (potential-dependent) structure of water adsorbed on solid surfaces [4]. However, basic insights into how a non-aqueous electrolyte–salt solution organizes at a solid interface, in particular from experiments, is still missing [5]. In many technological applications, the atomic scale properties of interfaces govern the functionality of the system. A prominent example is the importance of the structure and molecular arrangement of the liquid at the functional solid–liquid interface in batteries. More specifically, in LIBs, the arrangement of the electrolyte molecules directly at the electrode interface, and the electric double layer (EDL) formation are expected to govern the interfacial ion transport during charge/discharge, as well as affect the origin and properties of the solid electrolyte interphase (SEI).

Image: (a) Fresnel-normalized XRR (symbols) of the sapphire/LiPF₆:EC:DMC and corresponding model fits (lines). (b) Fit-derived electron density profiles. (c) Comparison of the XRR- and MD-derived (blue) density profiles. The MD-derived profile is smeared by the XRR-derived roughness. All curves are spaced vertically for clarity. (d) Periodicity at the solid/liquid interface vs. LiPF₆ concentration. (e) Normalized correlation lengths. (f) Schematic illustration of the proposed origin induced increased layer spacing with increasing salt-concentration.

Scientists decipher key principle behind reaction of metalloenzymes

2018/01/15

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how important bioinorganic electron transfer systems operate. Using a combination of very different, time-resolved measurement methods at DESY’s X-ray source PETRA III and other facilities, the scientists were able to show that so-called pre-distorted states can speed up photochemical reactions or make them possible in the first place. The group headed by Sonja Herres-Pawlis from the RWTH Aachen University Michael Rübhausen from the University of Hamburg and Wolfgang Zinth from Munich’s Ludwig Maximilian University, is presenting its findings in the journal Nature Chemistry.

The scientists had studied the pre-distorted, “entatic” state using a model system. An entatic state is the term used by chemists to refer to the configuration of a molecule in which the normal arrangement of the atoms is modified by external binding partners such that the energy threshold for the desired reaction is lowered, resulting in a higher speed of reaction. One example of this is the metalloprotein plastocyanin, which has a copper atom at its centre and is responsible for important steps in the transfer of electrons during photosynthesis. Depending on its oxidation state, the copper atom either prefers a planar configuration, in which all the surrounding atoms are arranged in the same plane (planar geometry), or a tetrahedral arrangement of the neighbouring ligands. However the binding partner in the protein forces the copper atom to adopt a sort of intermediate arrangement. This highly distorted tetrahedron allows a very rapid shift between the two oxidation states of the copper atom.

>Read more on the PETRA III website

Image Caption: Entatic state model complexes optimize the energies of starting and final configuration to enable fast reaction rates (illustrated by the hilly ground). The work demonstrates that the entatic state principle can be used to tune the photochemistry of copper complexes.
Credit: RWTH Aachen, Sonja Herres-Pawlis

Scientists measure accelerated emission

2017/12/292018/01/16

Grazing light for rapid events

An international team, including scientists from DESY, has verified a prediction about the quantum-mechanical behaviour of resonant systems made more than 50 years ago. In experiments at SACLA, the Japanese X-ray laser, and at the European Synchrotron Radiation Facility ESRF in France, the group led by Aleksandr Chumakov from ESRF could show a dramatic reduction in the time to emit the first X-ray photon from an ensemble of excited nuclei when the number of X-rays for the excitation was increased. This behaviour is in good agreement with one limit of a superradiant system, predicted by the US physicist Robert Dicke in 1954, as the scientists report in the journal Nature Physics.

One of the broad challenges of science is to understand the behaviour of groups of atoms based on the response of a single atom in isolation, which is usually much simpler. A facet of this is understanding the behaviour of a group of identical oscillators. An analogy is a collection of bells that all have the same tone: one can easily imagine the sound of a single bell struck once – a clear tone ringing out with a volume that decays away over time.

But what happens if one gently taps all the bells in a large collection? Will the tone be the same as a single one? What about the volume? What about the direction – does it matter where you are standing when you listen to the sound? Does it matter if you tap them all at the same time?

>Read more on the FLASH website