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

Students use AI for sample positioning at BioMAX

The samples at BioMAX beamline are very sensitive biomolecule crystals. It could, for example, be one of the many proteins you have in your body. They only last for a short time in the intense X-ray light before being damaged and needs to be placed exactly right before the researchers switch on the beam. In their masters’ project, Isak Lindhé, and Jonathan Schurmann have used methods of artificial intelligence to train the computer how to do it.

Hundreds of thousands of proteins
You have hundreds of thousands of different proteins in your body. They do everything from transporting oxygen in your blood to letting your cells take up nutrients after you’ve eaten or make your heart beat. And when things go wrong, you get prescribed medication. The pharmaceutical molecules connect to the proteins in your body to change how they work. To develop new pharmaceuticals with few side effects, the researchers, therefore, need to understand what different proteins look like in detail.

A tedious task
To get high-quality data from a sample it needs to be correctly positioned in the X-ray beam. The conventional model for finding the right position is to scan the sample in the beam to optimize the position. At MAX IV, the X-ray light is very intense, which is good because smaller crystals can be used. But at the same time, very often the sample can’t be scanned in the beam since it would be damaged long before the right position is found. The researchers, therefore, have to perform the rather tedious task of positioning it manually.

>Read more on the MAX IV Laboratory website

Nanoparticles form supercrystals under pressure

Investigations at Diamond may lead to easier ways to synthesise nanoparticle supercrystals

Self-assembly and crystallisation of nanoparticles (NPs) is generally a complex process, based on the evaporation or precipitation of NP-building blocks. Obtaining high-quality supercrystals is slow, dependent on forming and maintaining homogenous crystallisation conditions. Recent studies have used applied pressure as a homogeneous method to induce various structural transformations and phase transitions in pre-ordered nanoparticle assemblies. Now, in work recently published in the Journal of Physical Chemistry Letters, a team of German researchers studying solutions of gold nanoparticles coated with poly(ethylene glycol)- (PEG-) based ligands has discovered that supercrystals can be induced to form rapidly within the whole suspension.

>Read more on the Diamond Light Source website

Figure: 2D SAXS patterns of PEG-coated gold nanoparticles (AuNP) with 2 M CsCl added at different pressures. Left: 1 bar; Middle: 4000 bar; Right: After pressure release at 1 bar. The scheme on top illustrates the structural assembly of the coated AuNPs at different pressures: At 1 bar, the particle ensemble is in an amorphous, liquid state. Upon reaching the crystallization pressure, face-centred cubic crystallites are formed by the AuNPs. After pressure release, the AuNPs return to the liquid state. 

Movie directors with extra roles

Data storage devices based on novel materials are expected to make it possible to record information in a smaller space, at higher speed, and with greater energy efficiency than ever before.

Movies shot with the X-ray laser show what happens inside potential new storage media, as well as how the processes by which the material switches between two states can be optimised.
Henrik Lemke comes to work on his bicycle. Private cars are not allowed to drive to the SwissFEL building in the Würenlingen forest, and delivery vans and lorries need a permit. As a beamline scientist, the physicist is responsible for the experiment station named for Switzerland’s Bernina Pass. At the end of 2017, he led the first experiment at the Swiss free-electron X-ray laser, acting in effect as a movie director while SwissFEL was used, like a high-speed camera, to record how a material was selectively converted from a semiconducting to a conducting state – and back again. To this end the PSI team, together with a research group from the University of Rennes in France, studied a powder of nanocrystals made of titanium pentoxide. The sample was illuminated with infrared laser pulses that made the substance change its properties. Then X-ray pulses revealed how the crystal structure was deformed and enlarged – a cascade of dynamic processes that evidently depend on the size of the crystals.

Image: The directors: Henrik Lemke and Gerhard Ingold
Credit: Scanderbeg Sauer Photography

The enigma of Rembrandt’s vivid white

Some of Rembrandt’s masterpieces are at the ESRF for some days, albeit only in minuscule form. The goal: to unveil the secrets of the artist’s white pigment.

Seven medical students surround a dead body while they attentively look at how the doctor is dissecting the deceased. The scene is set in a dark and gloomy environment, where even the faces of the characters show a grey tinge. Strangely, the only light in the scene is that coming from their white collars and the white sheet that partially covers the body. The vivid white creates a perplexing light-reflecting effect. Welcome to painting The anatomy lesson of Dr. Nicolaes Tulp, a piece of art displaying the baffling technique of the impasto, of which Rembrandt, its author, was a master.

Impasto is thick paint laid on the canvas in an amount that makes it stand from the surface. The relief of impasto increases the perceptibility of the paint by increasing its light-reflecting textural properties. Scientists know that Rembrandt achieved the impasto effect by using materials traditionally available on the 17th century Dutch colour market, namely the lead white pigment (mix of hydrocerussite Pb3(CO3)2.(OH)2 and cerussite PbCO3), chalk (calcite CaCO3) and organic mediums (mainly linseed oil). The precise recipe he used is, however, still unknown.

>Read more on the European Synchrotron website

Image: The anatomy lesson of Dr. Nicolaes Tulp, by Rembrandt.

 

Respiratory virus study points to likely vaccine target

Scientists find a new way to make novel materials by ‘un-squeezing’

Like turning a snowball back into fluffy snow, a new technique turns high-density materials into a lower-density one by applying the chemical equivalent of ‘negative pressure.’

Some materials can morph into multiple crystal structures with very different properties. For instance, squeezing a soft form of carbon produces diamond, a harder and more brilliant form of carbon. The Kurt Vonnegut novel “Cat’s Cradle” featured ice-nine, a fictional form of water with a much higher melting point than regular ice that threatened to irreversibly freeze all the water on Earth.

These materials are called polymorphs, and they’re commonly made by applying pressure, or squeezing. Scientists looking for new materials would also like to do the opposite – apply “negative pressure” to stretch a material’s crystal structure into a new configuration. In the past, this approach seemed to require negative pressures that are difficult if not impossible to achieve in the lab, plus it risked pulling the material apart.

Now researchers at the Department of Energy’s National Renewable Energy Laboratory (NREL) have found a way to create the equivalent of negative pressure by mixing two materials together under just the right conditions to make an alloy with an airier and entirely different crystal structure and unique properties.

>Read more on the SSRL website

Image: SLAC staff scientists Laura Schelhas and Kevin Stone at an experimental station at the Stanford Synchrotron Radiation Lightsource, where they used X-rays to measure the structure of a novel ‘negative pressure’ material created at NREL.
Credit: Matt Beardsley/SLAC National Accelerator Laboratory

Study suggests water may exist in Earth’s lower mantle

Water on Earth runs deep – very deep. The oceans have been measured to a maximum depth of 7 miles, though water is known to exist well below the oceans. Just how deep this hidden water reaches, and how much of it exists, are the subjects of ongoing research.

Now a new study suggests that water may be more common than expected at extreme depths approaching 400 miles and possibly beyond – within Earth’s lower mantle. The study, which appeared March 8 in the journal Science, explored microscopic pockets of a trapped form of crystallized water molecules in a sampling of diamonds from around the world.

Diamond samples from locations in Africa and China were studied through a variety of techniques, including a method using infrared light at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Researchers used Berkeley Lab’s Advanced Light Source (ALS), and Argonne National Laboratory’s Advanced Photon Source, which are research centers known as synchrotron facilities.

>Read more on the Advanced Light Source website

Photo: Oliver Tschauner, professor of research in the Department of Geoscience at the University of Nevada, Las Vegas, holds a diamond sample during a recent round of experiments at Berkeley Lab’s Advanced Light Source.
Credit: Marilyn Chung/Berkeley Lab

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.

Examining the crystallisation during additive biomanufacturing

A research group from the University of Manchester has used wide-angle X-ray diffraction (XRD) in one of the first studies to investigate the evolution of crystallinity and crystal orientation in polycaprolactone (PCL) during 3D printing.

The team has developed a new extrusion-based printing machine, the Plasma-assisted Bioextrusion System (PABS). Extrusion-based techniques are widely used due to their versatility and simplicity, and their ability to print a range of materials in a cell-friendly environment, with high precision. PABS uses a novel approach for biomanufacturing and tissue engineering, combining screw-assisted extrusion, pressure-assisted extrusion and plasma jetting.

>Read more on the Diamond Light Source website

Figure: Conceptual material transition from extrusion-based filament printing to the partial replacement of a knee joint via 3D scaffolding.
Credit: Fengyuan Liu, Wajira Mirihanage, Paulo Bartolo, Medical Engineering Research Centre, the University of Manchester

The microstructure of a parrotfish tooth contributes to its toughness

During a 2012 visit to the Great Barrier Reef off the coast of Australia, ALS staff scientist Matthew Marcus became intrigued with parrotfish. “I was reminded that this is a fish that crunches up coral all day and is responsible for much of the white sand on beaches,” Marcus said. “But how can this fish eat coral and not lose its teeth?” So Marcus teamed up with Pupa Gilbert, a biophysicist at the University of Wisconsin–Madison, and an international team of researchers she assembled, to understand how parrotfish teeth work.

Because conventional microscopes can overlook the unique orientation of crystals in tooth enamel, the team used the technique called polarization-dependent imaging contrast (PIC) mapping that Gilbert invented, which uses the photoemission electron microscopy (PEEM) Beamline 11.0.1 at the ALS. The PIC maps allowed them to visualize the orientation of individual crystals of fluorapatite, the main mineral component of parrotfish teeth.

Separate experiments used tomography (Beamline 8.3.2) and microdiffraction (Beamline 12.3.2) to further analyze the crystal orientations and strains in the teeth.

>Read more on the ALS website

Image: (extract) PIC maps acquired at the tips of four different parrotfish teeth show that they consist of 100-nm-wide, microns-long crystals, bundled into “fibers” interwoven like warp and weft fibers in fabric. These fibers gradually decrease in average diameter from 5 μm at the back of a tooth to 2 μm at the tip. Intriguingly, this decrease in size is spatially correlated with an increase in hardness and stiffness. The orientation angle of the crystals is color-coded (chart at bottom).

 

Scientists observe nanowires as they grow

X-ray experiments reveal exact details of self-catalysed growth for the first time

At DESY’s X-ray source PETRA III, scientists have followed the growth of tiny wires of gallium arsenide live. Their observations reveal exact details of the growth process responsible for the evolving shape and crystal structure of the crystalline nanowires. The findings also provide new approaches to tailoring nanowires with desired properties for specific applications. The scientists, headed by Philipp Schroth of the University of Siegen and the Karlsruhe Institute of Technology (KIT), present their findings in the journal Nano Letters. The semiconductor gallium arsenide (GaAs) is widely used, for instance in infrared remote controls, the high-frequency components of mobile phones and for converting electrical signals into light for fibre optical transmission, as well as in solar panels for deployment in spacecraft.

To fabricate the wires, the scientists employed a procedure known as the self-catalysed Vapour-Liquid-Solid (VLS) method, in which tiny droplets of liquid gallium are first deposited on a silicon crystal at a temperature of around 600 degrees Celsius. Beams of gallium atoms and arsenic molecules are then directed at the wafer, where they are adsorpted and dissolve in the gallium droplets. After some time, the crystalline nanowires begin to form below the droplets, whereby the droplets are gradually pushed upwards. In this process, the gallium droplets act as catalysts for the longitudinal growth of the wires. “Although this process is already quite well established, it has not been possible until now to specifically control the crystal structure of the nanowires produced by it. To achieve this, we first need to understand the details of how the wires grow,” emphasises co-author Ludwig Feigl from KIT.

>Read more on the FLASH and PETRA III at DESY website

Image: A single nanowire, crowned by a gallium droplet, as seen with the scanning electron microscope (SEM) of the DESY NanoLab.
Credit: DESY, Thomas Keller

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.

 

ID23-EH2: Gearing up for serial crystallography

ID23-EH2 is up and running, catering to small samples and serial crystallography experiments. Its small beam and unique diffractometer are the trademarks of this new MX beamline.

“This is amazing”, says David Drew, a user from Stockholm University, on the new ID23-EH2. “There is a perfect beam line to be screening LCP crystals. After 5 years working on this… it is amazing to be able to speed up finding the best spot to collect”, he adds. Drew and his team are on ID23-EH2. They are the first users since ID23-EH2 opened for business this month and have just started the experiment. He works with his team in transport proteins, which carry nutrients across membrane proteins and are important drug targets. 

>Read more on the ESRF website

Picture: Max Nanao with the users from the University of Stockholm (Sweden).

 

2017 ANSTO, Australian Synchrotron Stephen Wilkins Medal awarded

Leonie van ‘t Hag has been awarded the Australian Synchrotron S. Wilkins Medal for her PhD thesis

The award recognises her research to improve the method to crystallise proteins and peptides in order to study their structure, using a technique called crystallography. “Leonie’s insights into crystallisation processes could significantly help the development of treatments for a variety of illnesses,” said Australian Synchrotron Director, Professor Andrew Peele.

Most solid material in the world is made of crystalline structures. Crystals are made up of rows and rows of atoms or molecules stacked up like boxes in a warehouse, in different arrangements.

The science of determining these atomic or molecular structures from crystalline materials is called crystallography.