Writing and deleting magnets with lasers

Scientists * have found a way to write and delete magnets in an alloy using a laser beam – a surprising effect.

* at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia in Charlottesville, USA

The reversibility of the process opens up new possibilities in the fields of material processing, optical technology, and data storage.
Researchers of the HZDR, an independent German research laboratory, studied an alloy of iron and aluminum. It is interesting as a prototype material because subtle changes to its atomic arrangement can completely transform its magnetic behavior. “The alloy possesses a highly ordered structure, with layers of iron atoms that are separated by aluminum atomic layers. When a laser beam destroys this order, the iron atoms are brought closer together and begin to behave like magnets,” says HZDR physicist Rantej Bali.

Bali and his team prepared a thin film of the alloy on top of transparent magnesia through which a laser beam was shone on the film. When they, together with researchers of the HZB, directed a well-focused laser beam with a pulse of 100 femtoseconds (a femtosecond is a millionth of a billionth of a second) at the alloy, a ferromagnetic area was formed. Shooting laser pulses at the same area again – this time at reduced laser intensity – was then used to delete the magnet.

>Read more on the Bessy II at HZB website

Image: Laser light for writing and erasing information – a strong laser pulse disrupts the arrangement of atoms in an alloy and creates magnetic structures (left). A second, weaker, laser pulse allows the atoms to return to their original lattice sites (right). (Find the entire image here)
Credit: Sander Münster / HZDR

Scientists use machine learning to speed discovery of metallic glass

In a new report, they combine artificial intelligence and accelerated experiments to discover potential alternatives to steel in a fraction of the time.

Blend two or three metals together and you get an alloy that usually looks and acts like a metal, with its atoms arranged in rigid geometric patterns.

But once in a while, under just the right conditions, you get something entirely new: a futuristic alloy called metallic glass that’s amorphous, with its atoms arranged every which way, much like the atoms of the glass in a window. Its glassy nature makes it stronger and lighter than today’s best steel, plus it stands up better to corrosion and wear.

Even though metallic glass shows a lot of promise as a protective coating and alternative to steel, only a few thousand of the millions of possible combinations of ingredients have been evaluated over the past 50 years, and only a handful developed to the point that they may become useful.

Now a group led by scientists at the Department of Energy’s SLAC National Accelerator Laboratory, the National Institute of Standards and Technology (NIST) and Northwestern University has reported a shortcut for discovering and improving metallic glass – and, by extension, other elusive materials – at a fraction of the time and cost.

>Read more on the SLAC website

Image: Fang Ren, who developed algorithms to analyze data on the fly while a postdoctoral scholar at SLAC, at a Stanford Synchrotron Radiation Lightsource beamline where the system has been put to use.
Credit: Dawn Harmer/SLAC National Accelerator Laboratory

Scientists develop sugar-coated nanosheets to target pathogens

Molecular Foundry-designed 2-D sheets mimic the surface of cells

Researchers have developed a process for creating ultrathin, self-assembling sheets of synthetic materials that can function like designer flypaper in selectively binding with viruses, bacteria, and other pathogens.
In this way the new platform, developed by a team led by scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), could potentially be used to inactivate or detect pathogens.

The team, which also included researchers from New York University, created the synthesized nanosheets at Berkeley Lab’s Molecular Foundry, a nanoscale science center, out of self-assembling, bio-inspired polymers known as peptoids. The study was published earlier this month in the journal ACS Nano.
The sheets were designed to present simple sugars in a patterned way along their surfaces, and these sugars, in turn, were demonstrated to selectively bind with several proteins, including one associated with the Shiga toxin, which causes dysentery. Because the outside of our cells are flat and covered with sugars, these 2-D nanosheets can effectively mimic cell surfaces.

>Read more on the Advanced Light Source website

Image: A molecular model of a peptoid nanosheet shows loop structures in sugars (orange) that bind to the Shiga toxin (shown as a five-color bound structure at upper right).
Credit: Berkeley Lab

Phase diagram leads the way to tailored metamaterial responses

Tuning the electronic structure of a 2D material

Stacked 2D materials possess an array of tunable properties that are expected to be important for future applications in electronics and optics.

When some atomically thin—or 2D—materials are stacked like Lego bricks in different combinations with other ultrathin materials, new properties often emerge that are potentially useful for next-generation device applications. For example, tungsten disulfide (WS2) is a semiconductor that belongs to a family of 2D materials (transition-metal dichalcogenides, or TMDs) that have received an enormous amount of interest due to their many advantageous properties that can be tuned by mixing and matching them in stacks with other 2D materials.

In this work, single-layer WS2 was stacked on a thin flake of hexagonal boron nitride (h-BN), all on a base of titanium dioxide (TiO2). This heterostructure provided a stable, non-interacting platform that enabled a team of researchers to directly and accurately probe the WS2 electronic states and excitations, including the effects of interactions between the electrons themselves (many-body effects), at a level of detail not previously possible.

MAESTRO’s exquisite sensitivity

MAESTRO (Microscopic and Electronic Structure Observatory), a facility at ALS Beamline 7.0.2 that opened to scientists in 2016, can handle very small sample sizes, on the order of tens of microns, which is key to studying 2D materials. Scientists are continuing to push MAESTRO’s capabilities to study even smaller features—down to the nanoscale. The endstation also features the ability to fabricate and manipulate samples for x-ray studies while maintaining pristine conditions that protect them from contamination.

>Read more on the Advanced Light Source website

Image: Rendering of the atomic structure of a 2D layer of tungsten disulfide, or WS2 (blue and yellow), on top of layers of 2D boron nitride (silver and gold). Above that is a representation of the WS2 conduction band (pink-edged metallic surface) and valence bands (green- and blue-edged metallic surfaces). The results of this experiment suggest that the observed increase in valence-band splitting could be due to the presence of “trions,” exotic three-particle combinations of holes and electrons (red circles), in the conduction and valence bands. The background shows the raw WS2 electronic-structure data, as measured in the experiment.
Credit: Chris Jozwiak/Berkeley Lab

Researchers obtain nanometric magnetite with full properties

When reducing materials at the nanoscale, they typically lose some of their properties. The experiments have been carried out at the CIRCE beamline of the ALBA Synchrotron.

Magnetite is a candidate material for various applications in spintronics, meaning that can be employed in devices where the spin of the electron is used to store or manipulate information. However, when it is necessary to create structures of the material at the nanometric scale, their properties get worse. A study, recently published in the scientific journal Nanoscale, has proved that, with suitable growth, magnetite could be used to create nanostructured magnetic elements without losing their properties.

“Oxides have been proposed to be used for spin waves in triangular structures for computing. And our results suggest that magnetite could be used for this purpose, “says Juan de la Figuera, scientist from the Spanish National Research Council (CSIC).

>Read more on the ALBA website

Image: Beamline involved where nanometric magnetite has been obtained, keeping its full properties.
Credit: ALBA

Marianne Liebi winner of Swedish L’Oréal-Unesco For Women in Science 2018

L’Oréal-Unesco For Women in Science Prize is awarded in Sweden for the third time. The purpose of the prize is to pay attention to and reward young women who have shown great potential in science, while offering positive female role-models. Researchers Marianne Liebi, Chalmers, and Ruth Pöttgen, Lund University, get L’Oréal-Unesco For Women in Science Award, supported by Sweden’s young academy 2018.

Marianne Liebi gets the award “for the constructive use of advanced imaging methods for biomaterials with the aim of understanding the connection between molecular and mechanical properties”. Marianne Liebi uses powerful X-ray technology to study how, for example, the smallest building blocks, collagen fibrils, the bone tissue, look and are organised. The goal is to develop a mimicking, biomimetic material, where nature’s own design principles are imitated and applied to develop artificial bone and cartilage.
“It’s important to show that in research, it does not matter where you come from or who you are – what matters is passion and dedication. At best, this kind of award will not be needed in the future, it would be aimed at all young researchers. It would not matter who you were, says Marianne Liebi.

>Read more on the MAXIV Laboratory website

Photo: Researchers Ruth Pöttgen (left), Lund University, and Marianne Liebi (right), Chalmers, get L’Oréal-Unesco For Women in Science Award 2018, supported by Young Academy Sweden.
Credit: Emma Burendahl

Stressing over new materials

Titanium is a workhorse metal of the modern age. Alloyed with small amounts of aluminum and vanadium, it is used in aircraft, premium sports equipment, race cars, space craft, high-end bicycles, and medical devices because of its light weight, ability to withstand extreme temperatures, and excellent corrosion resistance. But titanium is also expensive. Metallurgists would love to understand exactly what makes it so strong so that they could design other materials with similarly desirable properties out of more common, less expensive elements. Now, researchers utilizing the U.S. Department of Energy’s Advanced Photon Source (APS) have used high-intensity x-rays to show how titanium alloy responds to stress in its (until now) hidden interior. Eventually, the researchers believe they will be able to predict how strong a titanium part such as an aircraft engine will be, just by knowing how the crystals are arranged inside of it. And materials scientists may be able to use such a computational model to swap in atoms from different metals to see how their crystalline structures compare to that of titanium.

>Read more on the Advanced Photon Source website

Figure: (extract) (A) A computational model of crystals inside a block of titanium, (B) includes effects noticed during the experiment to place permanent deformations (the darkened areas,) [not visible here, entire picture here]  while (C) models permanent deformations without incorporating the diversity of load seen in the experiment.

X-ray imaging of gigahertz ferroelectric domain dynamics

A team of researchers has made an important advance in broadening our understanding of light-induced mesoscale dynamics using the U.S. Department of Energy’s Advanced Photon Source (APS) at Argonne National Laboratory. Time-resolved x-ray diffraction microscopy, aided by a newly developed dynamical phase-field method (DPFM), revealed how lattice waves can be excited by light pulses and the resulting local structural changes among mesoscopic domains in ferroelectrics, a widely utilized material for sensors, nanoscale positioners, and information storage devices.

Light interaction with matter offers a new way of controlling material properties by harnessing energy transport and conversion in functional materials without contact on ultrafast time scales. However, the desired dynamical control is complicated by the inhomogeneous response of real materials. The ultrafast dynamics depend not only on the intrinsic properties of the compound but also, strongly, on mesoscale structures such as surfaces, domains, interfaces, and defects that govern the coupling between various degrees of freedom.

>Read more on the Advanced Photon Source website

Figure: Schematic illustration of spatially-resolved pump-probe experiment and domain configuration of a BaTiO3 single crystal sample. The inset shows a unit cell of BaTiO3.

Scientists confirm speculation on the chemistry of a high-performance battery

X-ray experiments at Berkeley Lab reveal what’s at work in an unconventional electrode.

Scientists have discovered a novel chemical state of the element manganese. This chemical state, first proposed about 90 years ago, enables a high-performance, low-cost sodium-ion battery that could quickly and efficiently store and distribute energy produced by solar panels and wind turbines across the electrical grid.

This direct proof of a previously unconfirmed charge state in a manganese-containing battery component could inspire new avenues of exploration for battery innovations.

X-ray experiments at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) were key in the discovery. The study results were published Feb. 28 in the journal Nature Communications.

Scientists at Berkeley Lab and New York University participated in the study, which was led by researchers at Natron Energy, formerly Alveo Energy, a Santa Clara, California-based battery technology company.

The battery that Natron Energy supplied for the study features an unconventional design for an anode, which is one of its two electrodes. Compared with the relatively mature designs of anodes used in lithium-ion batteries, anodes for sodium-ion batteries remain an active focus of R&D.

>Read more on the Advanced Light Source website

Photo: An array of solar panels and windmills.
Credit: PxHere

Functionalized graphdiyne nanowires

… on-surface synthesis and assessment of band structure, flexibility, and information storage potential

With their extraordinary mechanical and electronic properties carbon-based nanomaterials are central in 21st century research and carry high hopes for future nanotechnology applications. Established sp2-hybridized scaffolds include carbon nanotubes (CNTs), graphene sheets, and graphene nanoribbons. Recently, the interest in carbon allotropes incorporating both sp2and sp-hybridized atoms rose tremendously, especially for the most popular member, the so-called graphdiyne. According to theory, the related nanomaterials possess characteristics desirable for applications such as molecular electronics, energy storage, gas filtering and light harvesting. However, achieving the targeted materials with high quality remained challenging until now.
Here, we employed covalent on-surface synthesis on well-defined metal substrates under ultra-high vacuum (UHV) conditions to the homocoupling reaction of terminal alkyne compounds and fabricated the first functionalized graphdiyne (f-GDY) nanowires. Combining the substrate templating of the Ag(455) vicinal surface with specifically designed CN-functionalized precursors we achieved the controlled polymerization to atom-precise strands with their length reaching 40 nm. The left panel of Figure 1a depicts a scanning tunneling microscopy (STM) image of an area of the silver surface featuring two step edges where an example of such a f-GDY wire is lying at the lower side of the right step edge. The right panel displays a molecular model of the situation highlighting the structure of the nanowire adsorbed in the lower terrace (darker blue) consisting of covalently coupled monomers (red outline) with the CN moieties pointing towards the atoms of the upper terrace (brighter blue).

>Read more on the Elettra Sincrotrone website

Figure: (extract)  Synthesis and characterization of functionalized graphdiyne nanowires. a) STM topograph of a f-GDY polymer covering the left step edge. b) ARPES data: Before annealing a non-dispersing feature originates from the HOMO of the monomer. After annealing a dispersing features (blue) can be identified. c) Schematic representation of the deduced intrinsic band structure of the f-GDY nanowires. d) STM topograph of a strongly bent nanowire. e) Information storage thru conformational cis-trans switching of benzonitrile units. Full image here.

FemtoMAX – an X-ray beamline for structural dynamics at a short-pulse facility

The FemtoMAX beamline facilitates studies of the structural dynamics of materials. Such studies are of fundamental importance for key scientific problems related to programming materials using light, enabling new storage media and new manufacturing techniques, obtaining sustainable energy by mimicking photosynthesis, and gleaning insights into chemical and biological functional dynamics. The FemtoMAX beamline utilizes the MAX IV linear accelerator as an electron source. The photon bursts have a pulse length of 100 fs, which is on the timescale of molecular vibrations, and have wavelengths matching interatomic distances (Å). The uniqueness of the beamline has called for special beamline components. This paper presents the beamline design including ultrasensitive X-ray beam-position monitors based on thin Ce:YAG screens, efficient harmonic separators and novel timing tools.

>Read more on the MAXIV Laboratory website

Image: Jörgen Larsson (right) and Christian Disch (left) looking at the first results from the Time-over-threshhold photon-counting detector, an important tool for background free measurements of SAXS and WAXS experiments with samples dissolved in liquids.

Atomic Flaws Create Surprising, High-Efficiency UV LED Materials

Subtle surface defects increase UV light emission in greener, more cost-effective LED and catalyst materials

Light-emitting diodes (LEDs) traditionally demand atomic perfection to optimize efficiency. On the nanoscale, where structures span just billionths of a meter, defects should be avoided at all costs—until now.

A team of scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University has discovered that subtle imperfections can dramatically increase the efficiency and ultraviolet (UV) light output of certain LED materials.

“The results are surprising and completely counterintuitive,” said Brookhaven Lab scientist Mingzhao Liu, the senior author on the study. “These almost imperceptible flaws, which turned out to be missing oxygen in the surface of zinc oxide nanowires, actually enhance performance. This revelation may inspire new nanomaterial designs far beyond LEDs that would otherwise have been reflexively dismissed.”

>Read more on the NSLS-II website

Image: The research team, front to back and left to right: Danhua Yan, Mingzhao Liu, Klaus Attenkoffer, Jiajie Cen, Dario Stacciola, Wenrui Zhang, Jerzy Sadowski, Eli Stavitski.

 

Liquid crystal molecules form nano rings

Quantised self-assembly enables design of materials with novel properties

At DESY’s X-ray source PETRA III, scientists have investigated an intriguing form of self-assembly in liquid crystals: When the liquid crystals are filled into cylindrical nanopores and heated, their molecules form ordered rings as they cool – a condition that otherwise does not naturally occur in the material. This behavior allows nanomaterials with new optical and electrical properties, as the team led by Patrick Huber from Hamburg University of Technology (TUHH) reports in the journal Physical Review Letters.

The scientists had studied a special form of liquid crystals that are composed of disc-shaped molecules called discotic liquid crystals. In these materials, the disk molecules can form high, electrically conductive pillars by themselves, stacking up like coins. The researchers filled discotic liquid crystals in nanopores in a silicate glass. The cylindrical pores had a diameter of only 17 nanometers (millionths of a millimeter) and a depth of 0.36 millimeters.

There, the liquid crystals were heated to around 100 degrees Celsius and then cooled slowly. The initially disorganised disk molecules formed concentric rings arranged like round curved columns. Starting from the edge of the pore, one ring after the other gradually formed with decreasing temperature until at about 70 degrees Celsius the entire cross section of the pore was filled with concentric rings. Upon reheating, the rings gradually disappeared again.

>Read more on the PETRA III at Desy website

Image: Stepwise self-organisation of the cooling liquid crystals. (Extract, see the entire image here)
Credit: A. Zantop/M. Mazza/K. Sentker/P. Huber, Max-Planck Institut für Dynamik und Selbstorganisation/Technische Universität Hamburg; Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores, Physical Review Letters, 2018; CC BY 4.

 

40-year controversy in solid-state physics resolved

An international team at BESSY II headed by Prof. Oliver Rader has shown that the puzzling properties of samarium hexaboride do not stem from the material being a topological insulator, as it had been proposed to be.

Theoretical and initial experimental work had previously indicated that this material, which becomes a Kondo insulator at very low temperatures, also possessed the properties of a topological insulator. The team has now published a compelling alternative explanation in Nature Communications, however.

Samarium hexaboride is a dark solid with metallic properties at room temperature. It hosts Samarium, an element having several electrons confined to localized f orbitals in which they interact strongly with one another. The lower the temperature, the more apparent these interactions become. SmB6 becomes what is known as a Kondo insulator, named after Jun Kondo who was first able to explain this quantum effect.

In spite of Kondo-Effect: some conductivity remains

About forty years ago, physicists observed that SmB6 still retained remnant conductivity at temperatures below 4 kelvin, the cause of which had remained unclear until today. After the discovery of the topological-insulator class of materials around 12 years ago, hypotheses grew insistent that SmB6 could be a topological insulator as well as being Kondo insulator, which might explain the conductivity anomaly at a very fundamental level, since this causes particular conductive states at the surface. Initial experiments actually pointed toward this.

>Read more on the Bessy II website

Image: Electrons with differing energies are emitted along various crystal axes in the interior of the sample as well as from the surface. These can be measured with the angular-resolved photoemission station (ARPES) at BESSY II. Left image shows the sample temperature at 25 K, right at only 1 K. The energy distribution of the conducting and valence band electrons can be derived from these data. The surface remains conductive at very low temperature (1 K).
Credit: Helmholtz Zentrum Berlin

Questioning the universality of the charge density wave nature…

… in electron-doped cuprates

The first superconductor materials discovered offer no electrical resistance to a current only at extremely low temperatures (less than 30 K or −243.2°C). The discovery of materials that show superconductivity at much higher temperatures (up to 138 K or −135°C) are called high-temperature superconductors (HTSC). For the last 30 years, scientists have researched cuprate materials, which contain copper-oxide planes in their structures, for their high-temperature superconducting abilities. To understand the superconducting behavior in the cuprates, researchers have looked to correlations with the charge density wave (CDW), caused by the ordered quantum field of electrons in the material. It has been assumed that the CDW in a normal (non-superconducting) state is indicative of the electron behavior at the lower temperature superconducting state. A team of scientists from SLAC, Japan, and Michigan compared the traits of superconducting and non-superconducting cuprate materials in the normal state to test if the CDW is correlated to superconductivity.

>Read more on the SSRL website

Picture: explanation in detail to read in the full scientific highlight (SSRL website)