From MIT News: “Physicists record ‘lifetime’ of graphene qubits”

From MIT News

December 31, 2018
Rob Matheson

Researchers from MIT and elsewhere have recorded the “temporal coherence” of a graphene qubit — how long it maintains a special state that lets it represent two logical states simultaneously — marking a critical step forward for practical quantum computing. Stock image

First measurement of its kind could provide stepping stone to practical quantum computing.

Researchers from MIT and elsewhere have recorded, for the first time, the “temporal coherence” of a graphene qubit — meaning how long it can maintain a special state that allows it to represent two logical states simultaneously. The demonstration, which used a new kind of graphene-based qubit, represents a critical step forward for practical quantum computing, the researchers say.

Superconducting quantum bits (simply, qubits) are artificial atoms that use various methods to produce bits of quantum information, the fundamental component of quantum computers. Similar to traditional binary circuits in computers, qubits can maintain one of two states corresponding to the classic binary bits, a 0 or 1. But these qubits can also be a superposition of both states simultaneously, which could allow quantum computers to solve complex problems that are practically impossible for traditional computers.

The amount of time that these qubits stay in this superposition state is referred to as their “coherence time.” The longer the coherence time, the greater the ability for the qubit to compute complex problems.

Recently, researchers have been incorporating graphene-based materials into superconducting quantum computing devices, which promise faster, more efficient computing, among other perks. Until now, however, there’s been no recorded coherence for these advanced qubits, so there’s no knowing if they’re feasible for practical quantum computing.

In a paper published today in Nature Nanotechnology, the researchers demonstrate, for the first time, a coherent qubit made from graphene and exotic materials. These materials enable the qubit to change states through voltage, much like transistors in today’s traditional computer chips — and unlike most other types of superconducting qubits. Moreover, the researchers put a number to that coherence, clocking it at 55 nanoseconds, before the qubit returns to its ground state.

The work combined expertise from co-authors William D. Oliver, a physics professor of the practice and Lincoln Laboratory Fellow whose work focuses on quantum computing systems, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT who researches innovations in graphene.

“Our motivation is to use the unique properties of graphene to improve the performance of superconducting qubits,” says first author Joel I-Jan Wang, a postdoc in Oliver’s group in the Research Laboratory of Electronics (RLE) at MIT. “In this work, we show for the first time that a superconducting qubit made from graphene is temporally quantum coherent, a key requisite for building more sophisticated quantum circuits. Ours is the first device to show a measurable coherence time — a primary metric of a qubit — that’s long enough for humans to control.”

There are 14 other co-authors, including Daniel Rodan-Legrain, a graduate student in Jarillo-Herrero’s group who contributed equally to the work with Wang; MIT researchers from RLE, the Department of Physics, the Department of Electrical Engineering and Computer Science, and Lincoln Laboratory; and researchers from the Laboratory of Irradiated Solids at the École Polytechnique and the Advanced Materials Laboratory of the National Institute for Materials Science.

A pristine graphene sandwich

Superconducting qubits rely on a structure known as a “Josephson junction,” where an insulator (usually an oxide) is sandwiched between two superconducting materials (usually aluminum). In traditional tunable qubit designs, a current loop creates a small magnetic field that causes electrons to hop back and forth between the superconducting materials, causing the qubit to switch states.

But this flowing current consumes a lot of energy and causes other issues. Recently, a few research groups have replaced the insulator with graphene, an atom-thick layer of carbon that’s inexpensive to mass produce and has unique properties that might enable faster, more efficient computation.

To fabricate their qubit, the researchers turned to a class of materials, called van der Waals materials — atomic-thin materials that can be stacked like Legos on top of one another, with little to no resistance or damage. These materials can be stacked in specific ways to create various electronic systems. Despite their near-flawless surface quality, only a few research groups have ever applied van der Waals materials to quantum circuits, and none have previously been shown to exhibit temporal coherence.

For their Josephson junction, the researchers sandwiched a sheet of graphene in between the two layers of a van der Waals insulator called hexagonal boron nitride (hBN). Importantly, graphene takes on the superconductivity of the superconducting materials it touches. The selected van der Waals materials can be made to usher electrons around using voltage, instead of the traditional current-based magnetic field. Therefore, so can the graphene — and so can the entire qubit.

When voltage gets applied to the qubit, electrons bounce back and forth between two superconducting leads connected by graphene, changing the qubit from ground (0) to excited or superposition state (1). The bottom hBN layer serves as a substrate to host the graphene. The top hBN layer encapsulates the graphene, protecting it from any contamination. Because the materials are so pristine, the traveling electrons never interact with defects. This represents the ideal “ballistic transport” for qubits, where a majority of electrons move from one superconducting lead to another without scattering with impurities, making a quick, precise change of states.

How voltage helps

The work can help tackle the qubit “scaling problem,” Wang says. Currently, only about 1,000 qubits can fit on a single chip. Having qubits controlled by voltage will be especially important as millions of qubits start being crammed on a single chip. “Without voltage control, you’ll also need thousands or millions of current loops too, and that takes up a lot of space and leads to energy dissipation,” he says.

Additionally, voltage control means greater efficiency and a more localized, precise targeting of individual qubits on a chip, without “cross talk.” That happens when a little bit of the magnetic field created by the current interferes with a qubit it’s not targeting, causing computation problems.

For now, the researchers’ qubit has a brief lifetime. For reference, conventional superconducting qubits that hold promise for practical application have documented coherence times of a few tens of microseconds, a few hundred times greater than the researchers’ qubit.

But the researchers are already addressing several issues that cause this short lifetime, most of which require structural modifications. They’re also using their new coherence-probing method to further investigate how electrons move ballistically around the qubits, with aims of extending the coherence of qubits in general.

See the full article here .

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From SLAC National Accelerator Lab: “Dancing atoms in perovskite materials provide insight into how solar cells work”

From SLAC National Accelerator Lab

November 6, 2018
Ali Sundermier

When the researchers scattered neutrons off the perovskite material (red beam) they were able to measure the energy the neutrons lost or gained (white and blue lines). Using this information, they were able to see the structure and motion of the atoms and molecules within the material (arrangement of blue and purple spheres). (Greg Stewart/SLAC National Accelerator Laboratory)

A new study is a step forward in understanding why perovskite materials work so well in energy devices and potentially leads the way toward a theorized “hot” technology that would significantly improve the efficiency of today’s solar cells.

A closer look at materials that make up conventional solar cells reveals a nearly rigid arrangement of atoms with little movement. But in hybrid perovskites, a promising class of solar cell materials, the arrangements are more flexible and atoms dance wildly around, an effect that impacts the performance of the solar cells but has been difficult to measure.

In a paper published in the PNAS, an international team of researchers led by the U.S. Department of Energy’s SLAC National Accelerator Laboratory has developed a new understanding of those wild dances and how they affect the functioning of perovskite materials. The results could explain why perovskite solar cells are so efficient and aid the quest to design hot-carrier solar cells, a theorized technology that would almost double the efficiency limits of conventional solar cells by converting more sunlight into usable electrical energy.

Piece of the puzzle

Perovskite solar cells, which can be produced at room temperature, offer a less expensive and potentially better performing alternative to conventional solar cell materials like silicon, which have to be manufactured at extremely high temperatures to eliminate defects. But a lack of understanding about what makes perovskite materials so efficient at converting sunlight into electricity has been a major hurdle to producing even higher efficiency perovskite solar cells.

“It’s really only been over the last five or six years that people have developed this intense interest in solar perovskite materials,” says Mike Toney, a distinguished staff scientist at SLAC’s Stanford Synchrotron Radiation Light Source (SSRL) who led the study.

SLAC/SSRL

“As a consequence, a lot of the foundational knowledge about what makes the materials work is missing. In this research, we provided an important piece of this puzzle by showing what sets them apart from more conventional solar cell materials. This provides us with scientific underpinnings that will allow us to start engineering these materials in a rational way.”

Keeping it hot

When sunlight hits a solar cell, some of the energy can be used to kick electrons in the material up to higher energy states. These higher-energy electrons are funneled out of the material, producing electricity.

But before this happens, a majority of the sun’s energy is lost to heat with some fraction also lost during the extraction of usable energy or due to inefficient light collection. In many conventional solar cells, such as those made with silicon, acoustic phonons – a sort of sound wave that propagates through material – are the primary way that this heat is carried through the material. The energy lost by the electron as heat limits the efficiency of the solar cell.

In this study, theorists from the United Kingdom, led by Imperial College Professor Aron Walsh and electronic structure theorists Jonathan Skelton and Jarvist Frost, provided a theoretical framework for interpreting the experimental results. They predicted that acoustic phonons traveling through perovskites would have short lifetimes as a result of the flexible arrangements of dancing atoms and molecules in the material.

Stanford chemists Hema Karunadasa and Ian Smith were able to grow the large, specialized single crystals that were essential for this work. With the help of Peter Gehring, a physicist at the NIST Center for Neutron Research, the team scattered neutrons off these perovskite single crystals in a way that allowed them to retrace the motion of the atoms and molecules within the material. This allowed them to precisely measure the lifetime of the acoustic phonons.

The research team found that in perovskites, acoustic phonons are incredibly short-lived, surviving for only 10 to 20 trillionths of a second. Without these phonons trucking heat through the material, the electrons might stay hot and hold onto their energy as they’re pulled out of the material. Harnessing this effect could potentially lead to hot-carrier solar cells with efficiencies that are nearly twice as high as conventional solar cells.

In addition, this phenomenon could explain how perovskite solar cells work so well despite the material being riddled with defects that would trap electrons and dampen performance in other materials.

“Since phonons in perovskites don’t travel very far, they end up heating the area surrounding the electrons, which might provide the boost the electrons need to escape the traps and continue on their merry way,” Toney says.

Transforming energy production

To follow up on this study, researchers at the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE) Energy Frontier Research Center led by DOE’s National Renewable Energy Laboratory will investigate this phenomenon in more complicated perovskite materials that are shown to be more efficient in energy devices. They would like to figure out how changing the chemical make-up of the material affects acoustic phonon lifetimes.

“We need to fundamentally transform our energy system as quickly as possible,” says Aryeh Gold-Parker, who co-led the study as a PhD student at Stanford University and SLAC. “As we move toward a low-carbon future, a very important piece is having cheap and efficient solar cells. The hope in perovskites is that they’ll lead to commercial solar panels that are more efficient and cheaper than the ones on the market today.”

The research team also included scientists from NIST; the University of Bath and Kings College London, both in the UK; and Yonsei University in Korea.

SSRL is a DOE Office of Science user facility. This work was supported by the DOE’s Office of Science and the Solar Energy Technologies Office; the Engineering and Physical Sciences Research Council; the Royal Society; and the Leverhulme Trust.

See the full article here .

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SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From SLAC National Accelerator Lab: “Scientists make first detailed measurements of key factors related to high-temperature superconductivity”

From SLAC National Accelerator Lab

October 31, 2018
Glennda Chui

A new study reveals how coordinated motions of copper (red) and oxygen (grey) atoms in a high-temperature superconductor boost the superconducting strength of pairs of electrons (white glow), allowing the material to conduct electricity without any loss at much higher temperatures. The discovery opens a new path to engineering higher-temperature superconductors. (Greg Stewart/SLAC National Accelerator Laboratory)

An illustration depicts the repulsive energy (yellow flashes) generated by electrons in one layer of a cuprate material repelling electrons in the next layer. Theorists think this energy could play a critical role in creating the superconducting state, leading electrons to form a distinctive form of “sound wave” that could boost superconducting temperatures. Scientists have now observed and measured those sound waves for the first time. (Greg Stewart/SLAC National Accelerator Laboratory)

In superconducting materials, electrons pair up and condense into a quantum state that carries electrical current with no loss. This usually happens at very low temperatures. Scientists have mounted an all-out effort to develop new types of superconductors that work at close to room temperature, which would save huge amounts of energy and open a new route for designing quantum electronics. To get there, they need to figure out what triggers this high-temperature form of superconductivity and how to make it happen on demand.

Now, in independent studies reported in Science and Nature, scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University report two important advances: They measured collective vibrations of electrons for the first time and showed how collective interactions of the electrons with other factors appear to boost superconductivity.

Carried out with different copper-based materials and with different cutting-edge techniques, the experiments lay out new approaches for investigating how unconventional superconductors operate.

“Basically, what we’re trying to do is understand what makes a good superconductor,” said co-author Thomas Devereaux, a professor at SLAC and Stanford and director of SIMES, the Stanford Institute for Materials and Energy Sciences, whose investigators led both studies.

“What are the ingredients that could give rise to superconductivity at temperatures well above what they are today?” he said. “These and other recent studies indicate that the atomic lattice plays an important role, giving us hope that we are gaining ground in answering that question.”

The high-temperature puzzle

Conventional superconductors were discovered in 1911, and scientists know how they work: Free-floating electrons are attracted to a material’s lattice of atoms, which has a positive charge, in a way that lets them pair up and flow as electric current with 100 percent efficiency. Today, superconducting technology is used in MRI machines, maglev trains and particle accelerators.

But these superconductors work only when chilled to temperatures as cold as outer space. So when scientists discovered in 1986 that a family of copper-based materials known as cuprates can superconduct at much higher, although still quite chilly, temperatures, they were elated.

The operating temperature of cuprates has been inching up ever since – the current record is about 120 degrees Celsius below the freezing point of water – as scientists explore a number of factors that could either boost or interfere with their superconductivity. But there’s still no consensus about how the cuprates function.

“The key question is how can we make all these electrons, which very much behave as individuals and do not want to cooperate with others, condense into a collective state where all the parties participate and give rise to this remarkable collective behavior?” said Zhi-Xun Shen, a SLAC/Stanford professor and SIMES investigator who participated in both studies.

Behind-the-scenes boost

One of the new studies, at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), took a systematic look at how “doping” – adding a chemical that changes the density of electrons in a material – affects the superconductivity and other properties of a cuprate called Bi2212.

SLAC/SSRL

SLAC/SSRL

Collaborating researchers at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan prepared samples of the material with slightly different levels of doping. Then a team led by SIMES researcher Yu He and SSRL staff scientist Makoto Hashimoto examined the samples at SSRL with angle-resolved photoemission spectroscopy, or ARPES. It uses a powerful beam of X-ray light to kick individual electrons out of a sample material so their momentum and energy can be measured. This reveals what the electrons in the material are doing.

In this case, as the level of doping increased, the maximum superconducting temperature of the material peaked and fell off again, He said.

The team focused in on samples with particularly robust superconducting properties. They discovered that three interwoven effects – interactions of electrons with each other, with lattice vibrations and with superconductivity itself – reinforce each other in a positive feedback loop when conditions are right, boosting superconductivity and raising the superconducting temperature of the material.

Small changes in doping produced big changes in superconductivity and in the electrons’ interaction with lattice vibrations, Devereaux said. The next step is to figure out why this particular level of doping is so important.

“One popular theory has been that rather than the atomic lattice being the source of the electron pairing, as in conventional superconductors, the electrons in high-temperature superconductors form some kind of conspiracy by themselves. This is called electronic correlation,” Yu He said. “For instance, if you had a room full of electrons, they would spread out. But if some of them demand more individual space, others will have to squeeze closer to accommodate them.”

In this study, He said, “What we find is that the lattice has a behind-the-scenes role after all, and we may have overlooked an important ingredient for high-temperature superconductivity for the past three decades,” a conclusion that ties into the results of earlier research by the SIMES group Science.

Electron ‘Sound Waves’

The other study, performed at the European Synchrotron Radiation Facility (ESRF) in France, used a technique called resonant inelastic X-ray scattering, or RIXS, to observe the collective behavior of electrons in layered cuprates known as LCCO and NCCO.

ESRF. Grenoble, France

RIXS excites electrons deep inside atoms with X-rays, and then measures the light they give off as they settle back down into their original spots.

In the past, most studies have focused only on the behavior of electrons within a single layer of cuprate material, where electrons are known to be much more mobile than they are between layers, said SIMES staff scientist Wei-Sheng Lee. He led the study with Matthias Hepting, who is now at the Max Planck Institute for Solid State Research in Germany.

But in this case, the team wanted to test an idea raised by theorists – that the energy generated by electrons in one layer repelling electrons in the next one plays a critical role in forming the superconducting state.

When excited by light, this repulsion energy leads electrons to form a distinctive sound wave known as an acoustic plasmon, which theorists predict could account for as much as 20 percent of the increase in superconducting temperature seen in cuprates.

With the latest in RIXS technology, the SIMES team was able to observe and measure those acoustic plasmons.

“Here we see for the first time how acoustic plasmons propagate through the whole lattice,” Lee said. “While this doesn’t settle the question of where the energy needed to form the superconducting state comes from, it does tell us that the layered structure itself affects how the electrons behave in a very profound way.”

This observation sets the stage for future studies that manipulate the sound waves with light, for instance, in a way that enhances superconductivity, Lee said. The results are also relevant for developing future plasmonic technology, he said, with a range of applications from sensors to photonic and electronic devices for communications.

SSRL is a DOE Office of Science user facility, and SIMES is a joint institute of SLAC and Stanford.

In addition to researchers from SLAC, Stanford and AIST, the study carried out at SSRL involved scientists from University of Tokyo; University of California, Berkeley; and Lorentz Institute for Theoretical Physics in the Netherlands.

The study conducted at ESRF also involved researchers from SSRL; Polytechnic University of Milan in Italy; ESRF; Binghamton University in New York; and the University of Maryland.

Both studies were funded by the DOE Office of Science.

See the full article here .

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SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From Brookhaven National Lab: “‘Choosy’ Electronic Correlations Dominate Metallic State of Iron Superconductor”

From Brookhaven National Lab

October 3, 2018
Ariana Tantillo
atantillo@bnl.gov

Finding could lead to a universal explanation of how two radically different types of materials—an insulator and a metal—can perfectly carry electrical current at relatively high temperatures.

Scientists discovered strong electronic correlations in certain orbitals, or energy shells, in the metallic state of the high-temperature superconductor iron selenide (FeSe). A schematic of the arrangement of the Se and Fe atoms is shown on the left; on the right is an image of the Se atoms in the termination layer of an FeSe crystal. Only the electron orbitals from the Fe atoms contribute to the orbital selectivity in the metallic state.

Two families of high-temperature superconductors (HTS)—materials that can conduct electricity without energy loss at unusually high (but still quite cold) temperatures—may be more closely related than scientists originally thought.

Beyond their layered crystal structures and the fact that they become superconducting when “doped” with atoms of other elements and cooled to a critical temperature, copper-based and iron-based HTS seemingly have little in common. After all, one material is normally an insulator (copper-based), and the other is a metal (iron-based). But a multi-institutional team of scientists has now presented new evidence suggesting that these radically different materials secretly share an important feature: strong electronic correlations. Such correlations occur when electrons move together in a highly coordinated way.

“Theory has long predicted that strong electronic correlations can remain hidden in plain sight in a Hund’s metal,” said team member J.C. Seamus Davis, a physicist in the Condensed Matter Physics and Materials Science at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell University. “A Hund’s metal is a unique new type of electronic fluid in which the electrons from different orbitals, or energy shells, maintain very different degrees of correlation as they move through the material. By visualizing the orbital identity and correlation strength for different electrons in the metal iron selenide (FeSe), we discovered that orbital-selective strong correlations are present in this iron-based HTS.”

It is yet to be determined if such correlations are characteristic of iron-based HTS in general. If proven to exist across both families of materials, they would provide the universal key ingredient in the recipe for high-temperature superconductivity. Finding this recipe has been a holy grail of condensed matter physics for decades, as it is key to developing more energy-efficient materials for medicine, electronics, transportation, and other applications.

Experiment meets theory

Since the discovery of iron-based HTS in 2008 (more than 20 years after that of copper-based HTS), scientists have been trying to understand the behavior of these unique materials. Confusion arose immediately because high-temperature superconductivity in copper-based materials emerges from a strongly correlated insulating state, but in iron-based HTS, it always emerges from a metallic state that lacks direct signatures of correlations. This distinction suggested that strong correlations were not essential—or perhaps even relevant—to high-temperature superconductivity. However, advanced theory soon provided another explanation. Because Fe-based materials have multiple active Fe orbitals, intense electronic correlations could exist but remain hidden due to orbital selectivity in the Hund’s metal state, yet still generate high-temperature superconductivity.

In this study, recently described in Nature Materials, the team—including Brian Andersen of Copenhagen University, Peter Hirschfeld of the University of Florida, and Paul Canfield of DOE’s Ames National Laboratory—used a scanning tunneling microscope to image the quasiparticle interference of electrons in FeSe samples synthesized and characterized at Ames National Lab. Quasiparticle interference refers to the wave patterns that result when electrons are scattered due to atomic-scale defects—such as impurity atoms or vacancies—in the crystal lattice.

The spectroscopic imaging scanning tunneling microscope used for this study, in three different views.

Spectroscopic imaging scanning tunneling microcopy can be used to visualize these interference patterns, which are characteristic of the microscopic behavior of electrons. In this technique, a single-atom probe moves back and forth very close to the sample’s surface in extremely tiny steps (as small as two trillionths of a meter) while measuring the amount of electrical current that is flowing between the single atom on the probe tip and the material, under an applied voltage.

Their analysis of the interference patterns in FeSe revealed that the electronic correlations are orbitally selective—they depend on which orbital each electron comes from. By measuring the strength of the electronic correlations (i.e., amplitude of the quasiparticle interference patterns), they determined that some orbitals show very weak correlation, whereas others show very strong correlation.

The next question to investigate is whether the orbital-selective electronic correlations are related to superconductivity. If the correlations act as a “glue” that binds electrons together into the pairs required to carry superconducting current—as is thought to happen in the copper-oxide HTS—a single picture of high-temperature superconductivity may emerge.

Experimental studies were carried out by the former Center for Emergent Superconductivity, a DOE Energy Frontier Research Center at Brookhaven, and the research was supported by DOE’s Office of Science, the Moore Foundation’s Emergent Phenomena in Quantum Physics (EPiQS) Initiative, and a Lundbeckfond Fellowship.

See the full article here .

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One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From ETH Zürich: “Materials of the future”

From ETH Zürich

01.10.2018
Oliver Morsch

In Paolo Ermanni’s laboratory at the ETH in Zürich, the composite materials of the future are developed. By optimizing the core elements of sandwich structures, the researchers create materials that are extremely light, robust and adaptable at once – and thus ideal for aerospace applications.

Lightweight sandwich structures. The cores of these composite materials contain a truss construction of carbon fibre rods. By optimizing the arrangement of the rods, the material can be tailored to specific applications. (Photograph: ETH Zürich / Christoph Karl, CMASLab)

Materials that are light and robust, inherently stable and still easily adjustable, and which can also be produced sustainably and in a resource-friendly way – what may appear as impossible as squaring the circle becomes a reality day after day in Paolo Ermanni’s lab at the ETH in Zürich. “It is our philosophy to develop modern composite materials for adaptive systems and, while doing so, to optimize their structural efficiency – that is, obtaining the same performance with fewer resources or better functionality with the same amount of material”, says Paolo Ermanni, professor for Composite Materials and Adaptive Structures at ETH. At the same time, he and his collaborators investigate appropriate production processes that make the new materials interesting for practical applications.

Truss structures in sandwiches

Ermanni’s PhD student Christoph Karl takes care of the “structural efficiency” aspect. “As they feature a large stiffness and stability whilst also being very light, sandwich structures are often used for lightweight construction”, he explains. Sandwich structures typically consist of two thin and stiff cover layers and a low-density core material. “In our research we develop high-performance sandwich composites made of carbon fibre-reinforced polymers, also known as CRP’s or simply carbon fibre. In this approach, the core consists of a truss structure of carbon fibre rods”, says Karl. The good mechanical properties of carbon fibre mean that such core structures can have a larger stiffness and stability than conventional foam or honeycomb cores.

According to Karl, another significant advantage of the truss cores is the possibility of a load-optimized design: “The mechanical properties of the sandwich composite depend strongly on the core topology – in other words, on the arrangement and orientation of the rods inside the core. With the help of numerical optimizations, we can tailor the orientation of the rods to specific external loads and thus maximize the structural efficiency for a particular application.”

Applications in aerospace engineering

The core of a sandwich material constructed and optimized in this way weighs less than 30 kilograms per cubic metre (a cubic metre of steel, for comparison, weighs in at almost 8000 kilograms). “This makes ours materials particularly interesting for aerospace application, where structural efficiency is of crucial importance,” says Karl. “Moreover, it is possible to integrate additional features, such as vibration damping, directly into the core structure.” In the framework of the EU project ALTAIR led by the French aerospace lab Onera, real-life applications of the new sandwich structures are investigated. Within that project, Ermanni’s research group is involved in the development of load-bearing structures of new deployment systems for small satellites.

Futuristic car components

Flexible and adaptive structures, on the other hand, are the specialty of PhD student Oleg Testoni. Within the Strategic Focus Area “Advanced Manufacturing” of the ETH board, he develops techniques that allow one to adapt sandwich structures flexibly and dynamically. Those techniques could be used, for instance, to build futuristic spoilers or wheelhouses for sports cars that can be deformed while the vehicle is in motion in order to accurately optimize its aerodynamics for a particular velocity or wheel position when cornering.

Oleg Testoni explains his research in the field of adaptive structures. (Video: ETH Zürich / Industry Relations)

Switches in the material

To achieve such a degree of flexibility whilst maintaining the robustness of the material, semi-active elements – so-called mechanical switches – are embedded in the material. “With such switches, the rods inside the core can be temporarily loosened in order to adapt the shape. After that, they are locked in place again so that the material regains its original stiffness”, Testoni explains.

Mechanical switches can be built using “intelligent materials” such as shape memory alloys. A component made of such an alloy can take on two different shapes depending on temperature. Above a certain critical temperature, its shape changes, but when cooled down it goes back to its exact original shape. By fitting many of those mechanical switches inside the rods of a sandwich structure, one can change the shape of the entire material.

3D-printing for carbon fibre cores

Ermanni and his co-workers do not just carry out basic research on new materials, however. The spin-off company 9T Labs, co-founded by Ermanni’s PhD student Martin Eichenhofer, develops a 3D-printing technology that can be used to produce high-quality carbon fibre components such as the rods for sandwich structure cores in a robust and flexible manner. “First and foremost, this is about expanding the range of application of such materials through novel production techniques, which will enable smaller companies to use them as well. This ‹democratizes› lightweight construction technologies, as it were,” says Eichenhofer. The first products for 3D-printing are supposed to hit the market as early as 2019. “This procedure also opens up the possibility of integrating active elements directly into the printing process in the future, thus realizing 4D-printing,” Ermanni adds.

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ETH Zürich is one of the leading international universities for technology and the natural sciences. It is well known for its excellent education, ground-breaking fundamental research and for implementing its results directly into practice.

Founded in 1855, ETH Zürich today has more than 18,500 students from over 110 countries, including 4,000 doctoral students. To researchers, it offers an inspiring working environment, to students, a comprehensive education.

Twenty-one Nobel Laureates have studied, taught or conducted research at ETH Zürich, underlining the excellent reputation of the university.

From Pacific Northwest National Lab: “PNNL’s capabilities in quantum information sciences get boost from DOE grant and new Microsoft partnership”

From Pacific Northwest National Lab

September 28, 2018
Susan Bauer, PNNL,
susan.bauer@pnnl.gov
(509) 372-6083

No image caption or credit

On Monday, September 24, the U.S. Department of Energy announced $218 million in funding for dozens of research awards in the field of Quantum Information Science. Nearly $2 million was awarded to DOE’s Pacific Northwest National Laboratory for a new quantum computing chemistry project.

“This award will be used to create novel computational chemistry tools to help solve fundamental problems in catalysis, actinide chemistry, and materials science,” said principal investigator Karol Kowalski. “By collaborating with the quantum computing experts at Lawrence Berkeley National Laboratory, Oak Ridge National Laboratory, and the University of Michigan, we believe we can help reshape the landscape of computational chemistry.”

Kowalski’s proposal was chosen along with 84 others to further the nation’s research in QIS and lay the foundation for the next generation of computing and information processing as well as an array of other innovative technologies.

While Kowalski’s work will take place over the next three years, computational chemists everywhere will experience a more immediate upgrade to their capabilities in computational chemistry made possible by a new PNNL-Microsoft partnership.

“We are working with Microsoft to combine their quantum computing software stack with our expertise on high-performance computing approaches to quantum chemistry,” said Sriram Krishnamoorthy who leads PNNL’s side of this collaboration.

Microsoft will soon release an update to the Microsoft Quantum Development Kit which will include a new chemical simulation library developed in collaboration with PNNL. The library is used in conjunction with NWChem, an open source, high-performance computational chemistry tool funded by DOE. Together, the chemistry library and NWChem will help enable quantum solutions and allow researchers and developers a higher level of study and discovery.

“Researchers everywhere will be able to tackle chemistry challenges with an accuracy and at a scale we haven’t experienced before,” said Nathan Baker, director of PNNL’s Advanced Computing, Mathematics, and Data Division. Wendy Shaw, the lab’s division director for physical sciences, agrees with Baker. “Development and applications of quantum computing to catalysis problems has the ability to revolutionize our ability to predict robust catalysts that mimic features of naturally occurring, high-performing catalysts, like nitrogenase,” said Shaw about the application of QIS to her team’s work.

PNNL’s aggressive focus on quantum information science is driven by a research interest in the capability and by national priorities. In September, the White House published the National Strategic Overview for Quantum Information Science and hosted a summit on the topic. Through their efforts, researchers hope to unleash quantum’s unprecedented processing power and challenge traditional limits for scaling and performance.

In addition to the new DOE funding, PNNL is also pushing work in quantum conversion through internal investments. Researchers are determining which software architectures allow for efficient use of QIS platforms, designing QIS systems for specific technologies, imagining what scientific problems can best be solved using QIS systems, and identifying materials and properties to build quantum systems. The effort is cross-disciplinary; PNNL scientists from its computing, chemistry, physics, and applied mathematics domains are all collaborating on quantum research and pushing to apply their discoveries. “The idea for this internal investment is that PNNL scientists will take that knowledge to build capabilities impacting catalysis, computational chemistry, materials science, and many other areas,” said Krishnamoorthy.

Krishnamoorthy wants QIS to be among the priorities that researchers think about applying to all of PNNL’s mission areas. With continued investment from the DOE and partnerships with industry leaders like Microsoft, that just might happen.

See the full article here .

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Pacific Northwest National Laboratory (PNNL) is one of the United States Department of Energy National Laboratories, managed by the Department of Energy’s Office of Science. The main campus of the laboratory is in Richland, Washington.

PNNL scientists conduct basic and applied research and development to strengthen U.S. scientific foundations for fundamental research and innovation; prevent and counter acts of terrorism through applied research in information analysis, cyber security, and the nonproliferation of weapons of mass destruction; increase the U.S. energy capacity and reduce dependence on imported oil; and reduce the effects of human activity on the environment. PNNL has been operated by Battelle Memorial Institute since 1965.

From Brookhaven National Lab: “Lining Up the Surprising Behaviors of a Superconductor with One of the World’s Strongest Magnets”

From Brookhaven National Lab

August 8, 2018

atantillo@bnl.gov
Ariana Tantillo
(631) 344-2347

Peter Genzer,
genzer@bnl.gov
(631) 344-3174

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way—a finding that could help direct the search for materials that can perfectly conduct electricity at room temperature.

(Clockwise from back left) Brookhaven Lab physicists Ivan Bozovic, Anthony Bollinger, and Jie Wu, and postdoctoral researcher Xi He used the molecular beam epitaxy system seen above to synthesize perfect single-crystal thin films made of lanthanum, strontium, oxygen, and copper (LSCO). They brought these superconducting films to the National High Magnetic Field Laboratory to see how the electrical resistance of LSCO in its “strange” metallic state changes under extremely strong magnetic fields.

What happens when really powerful magnets—capable of producing magnetic fields nearly two million times stronger than Earth’s—are applied to materials that have a “super” ability to conduct electricity when chilled by liquid nitrogen? A team of scientists set out to answer this question in one such superconductor made of the elements lanthanum, strontium, copper, and oxygen (LSCO). They discovered that the electrical resistance of this copper-oxide compound, or cuprate, changes in an unusual way when very high magnetic fields suppress its superconductivity at low temperatures.

“The most pressing problem in condensed matter physics is understanding the mechanism of superconductivity in cuprates because at ambient pressure they become superconducting at the highest temperature of any currently known material,” said physicist Ivan Bozovic, who leads the Oxide Molecular Beam Epitaxy Group at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and who is a coauthor of the Aug. 3 Science paper reporting the discovery. “This new result—that the electrical resistivity of LSCO scales linearly with magnetic field strength at low temperatures—provides further evidence that high-temperature superconductors do not behave like ordinary metals or superconductors. Once we can come up with a theory to explain their unusual behavior, we will know whether and where to search for superconductors that can carry large amounts of electrical current at higher temperatures, and perhaps even at room temperature.”

Cuprates such as LSCO are normally insulators. Only when they are cooled to some hundred degrees below zero and the concentrations of their chemical composition are modified (a process called doping) to a make them metallic can their mobile electrons pair up to form a “superfluid” that flows without resistance. Scientists hope that understanding how cuprates achieve this amazing feat will enable them to develop room-temperature superconductors, which would make energy generation and delivery significantly more efficient and less expensive.

In 2016, Bozovic’s group reported that LSCO’s superconducting state is nothing like the one explained by the generally accepted theory of classical superconductivity; it depends on the number of electron pairs in a given volume rather than the strength of the electron pairing interaction. In a follow-up experiment published the following year, they obtained another puzzling result: when LSCO is in its non-superconducting (normal, or “metallic”) state, its electrons do not behave as a liquid, as would be expected from the standard understanding of metals.

“The condensed matter physics community has been divided about this most basic question: do the behaviors of cuprates fall within existing theories for superconductors and metals, or are there profoundly different physical principles involved?” said Bozovic.

Continuing this comprehensive multipart study that began in 2005, Bozovic’s group and collaborators have now found additional evidence to support the latter idea that the existing theories are incomplete. In other words, it is possible that these theories do not encompass every known material. Maybe there are two different types of metals and superconductors, for example.

“This study points to another property of the strange metallic state in the cuprates that is not typical of metals: linear magnetoresistance at very high magnetic fields,” said Bozovic. “At low temperatures where the superconducting state is suppressed, the electrical resistivity of LSCO scales linearly (in a straight line) with the magnetic field; in metals, this relationship is quadratic (forms a parabola).”

This composite image offers a glimpse inside the custom-designed molecular beam epitaxy system that the Brookhaven physicists use to create single-crystal thin films for studying the properties of superconducting cuprates.

In order to study magneto resistance, Bozovic and group members Anthony Bollinger, Xi He, and Jie Wu first had to create flawless single-crystal thin films of LSCO near its optimal doping level. They used a technique called molecular beam epitaxy, in which separate beams containing atoms of the different chemical elements are fired onto a heated single-crystal substrate. When the atoms land on the substrate surface, they condense and slowly grow into ultra-thin layers, building a single atomic layer at a time. The growth of the crystal occurs in highly controlled conditions of ultra-high vacuum to ensure that the samples do not get contaminated.

“Brookhaven Lab’s key contribution to this study is this material synthesis platform,” said Bozovic. “It allows us to tailor the chemical composition of the films for different studies and provides the foundation for us to observe the true properties of superconducting materials, as opposed to properties induced by sample defects or impurities.”

The scientists then patterned the thin films onto strips containing voltage leads so that the amount of electrical current flowing through LSCO under an applied magnetic field could be measured.

They conducted initial magneto resistivity measurements with two 9 Tesla magnets at Brookhaven Lab—for reference, the strength of the magnets used in today’s magnetic resonance imaging (MRI) machines are typically up to 3 Tesla. Then, they brought their best samples (those with the best structural and transport qualities) to the Pulsed Field Facility. Located at DOE’s Los Alamos National Laboratory, this international user facility is part of the National High Magnetic Field Laboratory, which houses some of the strongest magnets in the world. Scientists at the Pulsed Field Facility placed the samples in an 80 Tesla pulsed magnet, powered by quick pulses, or shots, of electrical current. The magnet produces such large magnetic fields that it cannot be energized for more than a very short period of time (microseconds to a fraction of a second) without destroying itself.

“This large magnet, which is the size of a room and draws the electricity of a small city, is the only such installation on this continent,” said Bozovic. “We only get access to it once a year if we are lucky, so we chose our best samples to study.”

In October, the scientists will get access to a stronger (90 Tesla) magnet, which they will use to collect additional magneto resistance data to see if the linear relationship still holds.

An example of a typical device that the scientists use to measure electrical resistivity as a function of temperature and magnetic field. The scientists grew the film via atomic layer-by-layer molecular beam epitaxy, patterned it into a device, and wire bonded it to a chip carrier.

“While I do not expect to see something different, this higher field strength will allow us to expand the range of doping levels at which we can suppress superconductivity,” said Bozovic. “Collecting more data over a broader range of chemical compositions will help theorists formulate the ultimate theory of high-temperature superconductivity in cuprates.”

In the next year, Bozovic and the other physicists will collaborate with theorists to interpret the experimental data.

“It appears that the strongly correlated motion of electrons is behind the linear relationship we observed,” said Bozovic. “There are various ideas of how to explain this behavior, but at this point, I would not single out any of them.”

See the full article here .

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BNL RHIC Campus

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BNL RHIC PHENIX

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From SLAC Lab: “In a first, scientists precisely measure how synthetic diamonds grow”

From SLAC Lab

August 2, 2018
Glennda Chui

A SLAC-Stanford study has precisely measured for the first time how synthetic diamonds grow from diamondoid seeds, like the one at left. (Greg Stewart, SLAC National Accelerator Laboratory)

A SLAC-Stanford study reveals exactly what it takes for diamond to crystallize around a “seed” cluster of atoms. The results apply to industrial processes and to what happens in clouds overhead.

Natural diamond is forged by tremendous pressures and temperatures deep underground. But synthetic diamond can be grown by nucleation, where tiny bits of diamond “seed” the growth of bigger diamond crystals. The same thing happens in clouds, where particles seed the growth of ice crystals that then melt into raindrops.

Scientists have now observed for the first time how diamonds grow from seed at an atomic level, and discovered just how big the seeds need to be to kick the crystal growing process into overdrive.

The results, published this week in Proceedings of the National Academy of Sciences, shed light on how nucleation proceeds not just in diamonds, but in the atmosphere, in silicon crystals used for computer chips and even in proteins that clump together in neurological diseases.

“Nucleation growth is a core tenet of materials science, and there’s a theory and a formula that describes how this happens in every textbook,” says Nicholas Melosh, a professor at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory who led the research. “It’s how we describe going from one material phase to another, for example from liquid water to ice.”

But interestingly, he says, “despite the widespread use of this process everywhere, the theory behind it had never been tested experimentally, because observing how crystal growth starts from atomic-scale seeds is extremely difficult.”

An illustration shows how diamondoids (left), the tiniest possible specks of diamond, were used to seed the growth of nanosized diamond crystals (right). Trillions of diamondoids were attached to the surface of a silicon wafer, which was then tipped on end and exposed to a hot plasma (purple) containing carbon and hydrogen, the two elements needed to form diamond. A new study found that diamond growth really took off when seeds contained at least 26 carbon atoms. (Greg Stewart/SLAC National Accelerator Laboratory)

The smallest possible specks

In fact, scientists have known for a long time that the current theory often overestimates how much energy it takes to kick off the nucleation process, and by quite a bit. They’ve come up with potential ways to reconcile the theory with reality, but until now those ideas have been tested only at a relatively large scale, for instance with protein molecules, rather than at the atomic scale where nucleation begins.

To see how it works at the smallest scale, Melosh and his team turned to diamondoids, the tiniest possible bits of diamond. The smallest ones contain just 10 carbon atoms. These specks are the focus of a DOE-funded program at SLAC and Stanford where naturally occurring diamondoids are isolated from petroleum fluids, sorted by size and shape and studied. Recent experiments suggest they could be used as Lego-like blocks for assembling nanowires or “molecular anvils” for triggering chemical reactions, among other things.

The latest round of experiments was led by Stanford postdoctoral researcher Matthew Gebbie. He’s interested in the chemistry of interfaces – places where one phase of matter encounters another, for instance the boundary between air and water. It turns out that interfaces are incredibly important in growing diamonds with a process called CVD, or chemical vapor deposition, that’s widely used to make synthetic diamond for industry and jewelry.

“What I’m excited about is understanding how size and shape and molecular structure influence the properties of materials that are important for emerging technologies,” Gebbie says. “That includes nanoscale diamonds for use in sensors and in quantum computing. We need to make them reliably and with consistently high quality.”

Diamond or pencil lead?

To grow diamond in the lab with CVD, tiny bits of crushed diamond are seeded onto a surface and exposed to a plasma – a cloud of gas heated to such high temperatures that electrons are stripped away from their atoms. The plasma contains hydrogen and carbon, the two elements needed to form a diamond.

This plasma can either dissolve the seeds or make them grow, Gebbie says, and the competition between the two determines whether bigger crystals form. Since there are many ways to pack carbon atoms into a solid, it all has to be done under just the right conditions; otherwise you can end up with graphite, commonly known as pencil lead, instead of the sparkly stuff you were after.

Diamondoid seeds give scientists a much finer level of control over this process. Although they’re too small to see directly, even with the most powerful microscopes, they can be precisely sorted according to the number of carbon atoms they contain and then chemically attached to the surface of a silicon wafer so they’re pinned in place while being exposed to plasma. The crystals that grow around the seeds eventually get big enough to count under a microscope, and that’s what the researchers did.

The magic number is 26

Although diamondoids had been used to seed the growth of diamonds before, these were the first experiments to test the effects of using seeds of various sizes. The team discovered that crystal growth really took off with seeds that contain at least 26 carbon atoms.

Even more important, Gebbie says, they were able to directly measure the energy barrier that diamondoid particles have to overcome in order to grow into crystals.

“It was thought that this barrier must be like a gigantic mountain that the carbon atoms should not be able to cross – and, in fact, for decades there’s been an open question of why we could even make diamonds in the first place,” he says. “What we found was more like a mild hill.”

Gebbie adds, “This is really fundamental research, but at the end of the day, what we’re really excited about and driving for is a predictable and reliable way to make diamond nanomaterials. Now that we’ve developed the underlying scientific knowledge needed to do that, we’ll be looking for ways to put these diamond nanomaterials to practical use.”

This research took place at SIMES, the Stanford Institute for Materials and Energy Sciences, with major funding from the DOE Office of Science. In addition to SLAC and Stanford, researchers contributing to this study came from the Institute of Physics of the Czech Academy of Sciences, University Hasselt in Belgium and the Institute of Organic Chemistry at Justus-Liebig University in Germany.

See the full article here .

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SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From SLAC Lab: “X-Ray Experiment Confirms Theoretical Model for Making New Materials”

From SLAC Lab

July 2, 2018
Glennda Chui

In an experiment at SLAC, scientists loaded ingredients for making a material into a thin glass tube and used X-rays (top left) to observe the phases it went through as it was forming (shown in bubbles). The experiment verified theoretical predictions made by scientists at Berkeley Lab with the help of supercomputers (right). (Greg Stewart/SLAC National Accelerator Laboratory)

By observing changes in materials as they’re being synthesized, scientists hope to learn how they form and come up with recipes for making the materials they need for next-gen energy technologies.

Over the last decade, scientists have used supercomputers and advanced simulation software to predict hundreds of new materials with exciting properties for next-generation energy technologies.

Now they need to figure out how to make them.

To predict the best recipe for making a material, they first need a better understanding of how it forms, including all the intermediate phases it goes through along the way – some of which may be useful in their own right.

Now experiments at the Department of Energy’s SLAC National Accelerator Laboratory have confirmed the predictive power of a new computational approach to materials synthesis. Researchers say that this approach, developed at the DOE’s Lawrence Berkeley National Laboratory, could streamline the creation of novel materials for solar cells, batteries and other sustainable technologies.

“In the last 10 years, computational scientists have gotten really good at predicting the properties of new materials, but not so good at telling experimentalists like me how to make them,” said Michael Toney, a distinguished staff scientist at SLAC. “The theoretical framework developed at Berkeley Lab can help guide us in thinking about ways to synthesize and test these promising materials.”

This team described their findings June 29 in Nature Communications.

Metastable Materials

“Most theoretical approaches are great for predicting the endpoints of a reaction – what chemicals you start with, and what material you get at the end,” said study co-author Laura Schelhas, an associate staff scientist with SLAC’s Applied Energy Program. “But other interesting materials that form along the reaction pathway are often overlooked.”

These intermediate materials are said to exist in a state of metastability.

“Materials always want to be in their lowest-energy phase or ground state,” Schelhas explained. “Materials in a metastable state are higher in energy and will eventually transition to the more stable ground state. A diamond, for example, is a metastable state of carbon that will revert to its ground state, graphite, over millions of years.”

During synthesis, materials can crystallize into a series of metastable phases – some lasting only a few minutes, others persisting for hours. Some of these phases have properties that are potentially useful for technological applications. Others may block the formation of a material you want to make. Scientists want to isolate the useful phases and avoid creating the undesirable ones.

Co-authors Wenhao Sun and Gerbrand Ceder at Berkeley Lab and Daniil Kitchaev of the Massachusetts Institute of Technology recently developed a theoretical model to predict which metastable phases a material will form during synthesis.

“The key insight is to consider influences other than temperature and pressure that can affect a material’s formation,” Sun said. “For example, at a very small scale, surface energy is important, and impurities that materials take up from the surrounding environment can stabilize some types of crystalline structures. We developed a theory to quantify how these factors govern the formation of metastable phases, and then worked with SLAC to design an experiment to test it.”

The experiment, conducted at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), focused on manganese oxide, a compound whose formation can involve a variety of metastable crystalline structures. Some of these metastable structures are useful for battery applications or catalysis.

SLAC/SSRL

Schematic representation of remnant metastability in a crystallization pathway. a Free-energy of three phases (supersaturated solution (gray), M (green), S (blue)) as a function of the surface-area-to-volume ratio, 1/R (R is a particle radius). The gray line corresponds to the free-energy of a supersaturated solution, green is a metastable phase M that is size-stabilized by a low surface energy (given by the slope), and blue is the bulk equilibrium phase S, with high surface energy. b Phase diagram in the 1/R axis created from the projection of lowest free-energy phases. c A multistage crystallization pathway (red arrow in a ) proceeds downhill in energy, but phase transformations are limited by nucleation. Crystal growth of M prior to the induction of S means M can grow into a size-regime where phase M is metastable. S will then nucleate, and quickly grow by consuming M via dissolution-reprecipitation. The characteristic length scale of size-driven phase transitions lies in the 2 nm–50 nm range. Nature Communications

“Although manganese oxide has been widely studied, we still don’t have a good understanding of how to make specific metastable phases of the material,” Toney said. “Figuring out why certain recipes favor certain metastable structures will help us predict recipes for synthesizing not just this material, but others as well.”

Theory vs. Experiment

Sun and Schelhas designed an experiment to carefully manipulate a single ingredient in a recipe for making manganese oxide and track its effect on the formation of metastable crystals.

SLAC scientists led by postdoctoral researcher Bor-Rong Chen used powerful X-ray beams at SSRL to observe the chemical reaction as it happened.

“It’s pretty simple,” Schelhas said. “We load up manganese salts and other reaction materials into a small glass capillary, seal it and heat it. Then we shoot X-rays through the capillary while the reaction is occurring and watch the signal that reflects off the crystals. That signal allows us to determine the atomic structure of each metastable phase as it forms.”

At first, the metastable phases identified by X-ray diffraction didn’t seem to match the theoretical predictions, Chen said.

“We worked with the theorists at Berkeley Lab to retool the model,” she said, “and arrived at some explanations for why certain metastable phases might be skipped in a reaction, or why they might persist longer than we anticipated.”

To continue developing their understanding of synthesis, the researchers plan to conduct experiments on more complicated materials.

“This work marks only the initial steps in a much longer journey towards a predictive theory of materials synthesis,” Sun said. “Our goal is to build a powerful toolkit to design recipes for making exactly the materials we want.”

The team also found that they could stop the reaction at the point where a metastable material has formed, which will make it possible to test those materials for desirable properties in future studies, Schelhas said.

“We’re starting to push science into a new space in terms of understanding how you go about synthesis,” she added. “Predictive models have the potential to profoundly alter the way that materials design is done. That could greatly speed up the adoption of more advanced materials in areas like photovoltaics, batteries, thermoelectrics and a whole host of other sustainable technologies.”

Other co-authors of the study are from the Colorado School of Mines and the DOE’s National Renewable Energy Laboratory.

SSRL is a DOE Office of Science user facility. Funding for this work came from the Center for Next Generation of Materials Design, an Energy Frontier Research Center led by DOE’s National Renewable Energy Laboratory and funded by the DOE Office of Science.

See the full article here .

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SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From MIT: “How to bend and stretch a diamond”

MIT News

April 19, 2018
David L. Chandler

(Stellar-Serbia/iStock) via Science Alert

This scanning electron microscope image shows ultrafine diamond needles (cone shapes rising from bottom) being pushed on by a diamond tip (dark shape at top). These images reveal that the diamond needles can bend as much as 9 percent and still return to their original shape. Courtesy of the researchers.

The brittle material can turn flexible when made into ultrafine needles, researchers find.

Diamond is well-known as the strongest of all natural materials, and with that strength comes another tightly linked property: brittleness. But now, an international team of researchers from MIT, Hong Kong, Singapore, and Korea has found that when grown in extremely tiny, needle-like shapes, diamond can bend and stretch, much like rubber, and snap back to its original shape.

The surprising finding is being reported this week in the journal Science, in a paper by senior author Ming Dao, a principal research scientist in MIT’s Department of Materials Science and Engineering; MIT postdoc Daniel Bernoulli; senior author Subra Suresh, former MIT dean of engineering and now president of Singapore’s Nanyang Technological University; graduate students Amit Banerjee and Hongti Zhang at City University of Hong Kong; and seven others from CUHK and institutions in Ulsan, South Korea.

Experiment (left) and simulation (right) of a diamond nanoneedle being bent by the side surface of a diamond tip, showing ultralarge and reversible elastic deformation. No image credit.

The results, the researchers say, could open the door to a variety of diamond-based devices for applications such as sensing, data storage, actuation, biocompatible in vivo imaging, optoelectronics, and drug delivery. For example, diamond has been explored as a possible biocompatible carrier for delivering drugs into cancer cells.

The team showed that the narrow diamond needles, similar in shape to the rubber tips on the end of some toothbrushes but just a few hundred nanometers (billionths of a meter) across, could flex and stretch by as much as 9 percent without breaking, then return to their original configuration, Dao says.

Ordinary diamond in bulk form, Bernoulli says, has a limit of well below 1 percent stretch. “It was very surprising to see the amount of elastic deformation the nanoscale diamond could sustain,” he says.

“We developed a unique nanomechanical approach to precisely control and quantify the ultralarge elastic strain distributed in the nanodiamond samples,” says Yang Lu, senior co-author and associate professor of mechanical and biomedical engineering at CUHK. Putting crystalline materials such as diamond under ultralarge elastic strains, as happens when these pieces flex, can change their mechanical properties as well as thermal, optical, magnetic, electrical, electronic, and chemical reaction properties in significant ways, and could be used to design materials for specific applications through “elastic strain engineering,” the team says.

The team measured the bending of the diamond needles, which were grown through a chemical vapor deposition process and then etched to their final shape, by observing them in a scanning electron microscope while pressing down on the needles with a standard nanoindenter diamond tip (essentially the corner of a cube). Following the experimental tests using this system, the team did many detailed simulations to interpret the results and was able to determine precisely how much stress and strain the diamond needles could accommodate without breaking.

The researchers also developed a computer model of the nonlinear elastic deformation for the actual geometry of the diamond needle, and found that the maximum tensile strain of the nanoscale diamond was as high as 9 percent. The computer model also predicted that the corresponding maximum local stress was close to the known ideal tensile strength of diamond — i.e. the theoretical limit achievable by defect-free diamond.

When the entire diamond needle was made of one crystal, failure occurred at a tensile strain as high as 9 percent. Until this critical level was reached, the deformation could be completely reversed if the probe was retracted from the needle and the specimen was unloaded. If the tiny needle was made of many grains of diamond, the team showed that they could still achieve unusually large strains. However, the maximum strain achieved by the polycrystalline diamond needle was less than one-half that of the single crystalline diamond needle.

Yonggang Huang, a professor of civil and environmental engineering and mechanical engineering at Northwestern University, who was not involved in this research, agrees with the researchers’ assessment of the potential impact of this work. “The surprise finding of ultralarge elastic deformation in a hard and brittle material — diamond — opens up unprecedented possibilities for tuning its optical, optomechanical, magnetic, phononic, and catalytic properties through elastic strain engineering,” he says.

Huang adds “When elastic strains exceed 1 percent, significant material property changes are expected through quantum mechanical calculations. With controlled elastic strains between 0 to 9 percent in diamond, we expect to see some surprising property changes.”

The team also included Muk-Fung Yuen, Jiabin Liu, Jian Lu, Wenjun Zhang, and Yang Lu at the City University of Hong Kong; and Jichen Dong and Feng Ding at the Institute for Basic Science, in South Korea. The work was funded by the Research Grants Council of the Hong Kong Special Administrative Region, Singapore-MIT Alliance for Rresearch and Technology (SMART), Nanyang Technological University Singapore, and the National Natural Science Foundation of China.

See the full article here .

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The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.