From University of Oxford: “‘Impossible’ nano-sized protein cages made with the help of gold”

From University of Oxford

15 May 2019

A collaborative effort between the University of Oxford and the Malopolska Centre of Biotechnology, Jagiellonian University in Poland, has produced a super-stable artificial protein ball that apparently defies the rules of geometry and which may have applications in materials science and medicine.

Researchers are interested in making artificial protein cages in the hope that they can design them to have useful properties not found in nature. There are two challenges to achieving this goal. The first is the geometry problem: some proteins may have great potential utility but have the wrong shape to assemble into cages. The second problem is complexity: in nature the many proteins that form a protein cage are held together by a complex network of chemical bonds and these are very difficult to predict and simulate.

In new work, published in Nature, researchers found a way to solve both of these problems.

Professor Heddle, senior author of the research, said: ‘We were able to replace the complex interactions between proteins with a simple ‘staple’ consisting of a single gold atom. This simplifies the design problem and allows us to imbue the cages with new properties such as assembly and disassembly on demand.’

The research has also found a way to get around the geometrical problem: the building block of a protein cage is an 11-sided shape. Theoretically this should not be able to form the faces of a regular convex polyhedron. However the research has found that while this is mathematically true, some so-called ‘impossible shapes’ can assemble into cages which are so close to being regular that the errors are not noticeable.

Central to the study was the ability to characterise different cages, as well the ability to monitor and thereby understand the (dis)assembly dynamically. This work was done in the groups of Professors Justin Benesch and Philipp Kukura at Oxford, using innovative mass measurement approaches with a particular focus on biomolecular structure and assembly.

Justin Benesch, in the Department of Chemistry, said: ‘The ability to interrogate the cages using the advanced mass measurement approaches we have developed here in Oxford, both on the level of their assembly and the constituent building block, was key to not just validating their structure, but also the mechanism by which they are formed.’

The potential implications of the work are far-reaching. The researchers hope that the work can be expanded further to produce cages with new structures and new capabilities with potential applications particularly in drug delivery.

See the full article here.

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

Oxford is a collegiate university, consisting of the central University and colleges. The central University is composed of academic departments and research centres, administrative departments, libraries and museums. The 38 colleges are self-governing and financially independent institutions, which are related to the central University in a federal system. There are also six permanent private halls, which were founded by different Christian denominations and which still retain their Christian character.

The different roles of the colleges and the University have evolved over time.

From Oak Ridge National Laboratory: “New research facility will serve ORNL’s growing mission in computing, materials R&D”

From Oak Ridge National Laboratory

May 7, 2019
Bill H Cabage
cabagewh@ornl.gov
865-574-4399

Pictured in this early conceptual drawing, the Translational Research Capability planned for Oak Ridge National Laboratory will follow the design of research facilities constructed during the laboratory’s modernization campaign.

Energy Secretary Rick Perry, Congressman Chuck Fleischmann and lab officials today broke ground on a multipurpose research facility that will provide state-of-the-art laboratory space for expanding scientific activities at the Department of Energy’s Oak Ridge National Laboratory.

The new Translational Research Capability, or TRC, will be purpose-built for world-leading research in computing and materials science and will serve to advance the science and engineering of quantum information.

“Through today’s groundbreaking, we’re writing a new chapter in research at the Translational Research Capability Facility,” said U.S. Secretary of Energy Rick Perry. “This building will be the home for advances in Quantum Information Science, battery and energy storage, materials science, and many more. It will also be a place for our scientists, researchers, engineers, and innovators to take on big challenges and deliver transformative solutions.”

With an estimated total project cost of $95 million, the TRC, located in the central ORNL campus, will accommodate sensitive equipment, multipurpose labs, heavy equipment and inert environment labs. Approximately 75 percent of the facility will contain large, modularly planned and open laboratory areas with the rest as office and support spaces.

“This research and development space will advance and support the multidisciplinary mission needs of the nation’s advanced computing, materials research, fusion science and physics programs,” ORNL Director Thomas Zacharia said. “The new building represents a renaissance in the way we carry out research allowing more flexible alignment of our research activities to the needs of frontier research.”

The flexible space will support the lab’s growing fundamental materials research to advance future quantum information science and computing systems. The modern facility will provide atomic fabrication and materials characterization capabilities to accelerate the development of novel quantum computing devices. Researchers will also use the facility to pursue advances in quantum modeling and simulation, leveraging a co-design approach to develop algorithms along with prototype quantum systems.

The new laboratories will provide noise isolation, electromagnetic shielding and low vibration environments required for multidisciplinary research in quantum information science as well as materials development and performance testing for fusion energy applications. The co-location of the flexible, modular spaces will enhance collaboration among projects.

At approximately 100,000 square feet, the TRC will be similar in size and appearance to another modern ORNL research facility, the Chemical and Materials Sciences Building, which was completed in 2011 and is located nearby.

The facility’s design and location will also conform to sustainable building practices with an eye toward encouraging collaboration among researchers. The TRC will be centrally located in the ORNL main campus area on a brownfield tract that was formerly occupied by one of the laboratory’s earliest, Manhattan Project-era structures.

ORNL began a modernization campaign shortly after UT-Battelle arrived in 2000 to manage the national laboratory. The new construction has enabled the laboratory to meet growing space and infrastructure requirements for rapidly advancing fields such as scientific computing while vacating legacy spaces with inherent high operating costs, inflexible infrastructure and legacy waste issues.

The construction is supported by the Science Laboratory Infrastructure program of the DOE Office of Science.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

From Brookhaven National Lab: “New Lens System for Brighter, Sharper Diffraction Images”

From Brookhaven National Lab

April 25, 2019

Cara Laasch
laasch@bnl.gov
(631) 344-8458

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

Researchers from Brookhaven Lab designed, implemented, and applied a new and improved focusing system for electron diffraction measurements.

Mikhail Fedurin, Timur Shaftan, Victor Smalyuk, Xi Yang, Junjie Li, Lewis Doom, Lihua Yu, and Yimei Zhu are the Brookhaven team of scientists that realized and demonstrated the new lens system for as ultra-fast electron diffraction imaging.

To design and improve energy storage materials, smart devices, and many more technologies, researchers need to understand their hidden structure and chemistry. Advanced research techniques, such as ultra-fast electron diffraction imaging can reveal that information. Now, a group of researchers from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have developed a new and improved version of electron diffraction at Brookhaven’s Accelerator Test Facility (ATF)—a DOE Office of Science User Facility that offers advanced and unique experimental instrumentation for studying particle acceleration to researchers from all around the world. The researchers published their findings in Scientific Reports, an open-access journal by Nature Research.

Advancing a research technique such as ultra-fast electron diffraction will help future generations of materials scientists to investigate materials and chemical reactions with new precision. Many interesting changes in materials happen extremely quickly and in small spaces, so improved research techniques are necessary to study them for future applications. This new and improved version of electron diffraction offers a stepping stone for improving various electron beam-related research techniques and existing instrumentation.

“We implemented our new focusing system for electron beams and demonstrated that we can improve the resolution significantly when compared to the conventional solenoid technique,” said Xi Yang, author of the study and an accelerator physicist at the National Synchrotron Light Source II (NSLS-II) [see below], a DOE Office of Science User Facility at Brookhaven Lab. “The resolution mainly depends on the properties of light – or in our case – of the electron beam. This is universal for all imaging techniques, including light microscopy and x-ray imaging. However, it is much more challenging to focus the charged electrons to a near-parallel pencil-like beam at the sample than it would be with light, because electrons are negatively charged and therefore repulse one another. This is called the space charge effect. By using our new setup, we were able to overcome the space charge effect and obtain diffraction data that is three times brighter and two times sharper; it’s a major leap in resolution.”

The colorful images are four different electron diffraction measurements at ATF. The left column shows diffraction patterns of the sample using the newly developed quadrupoles, while the right column shows diffraction patterns without the new lens system. In the left column the rings of the pattern are sharper, rounder and turn red, which means that the overall resolution of the measurement is higher.

Every electron diffraction setup uses an electron beam that is focused on the sample so that the electrons bounce off the atoms in the sample and travel further to the detector behind the sample. The electrons create a so-called diffraction pattern, which can be translated into the structural makeup of the materials at the nanoscale. The advantage of using electrons to image this inner structure of materials is that the so called diffraction limit of electrons is very low, which means scientists can resolve smaller details in the structure compared to other diffraction methods.

A diverse team of researchers was needed to improve such a complex research method. The Brookhaven Lab team consisted of electron beam experts from the NSLS-II, electron accelerator experts from ATF, and materials science experts from the condensed matter physics & materials science (CMPMS) department.

“This advance would not have been possible without the combination of all our expertise across Brookhaven Lab. At NSLS-II, we have expertise on how to handle the electron beam. The ATF group brought the expertise and capabilities of the electron gun and laser technologies – both of which were needed to create the electron beam in the first place. And the CMPMS group has the sample expertise and, of course, drives the application needs. This is a unique synergy and, together, we were able to show how the resolution of the technique can be improved drastically,” said Li Hua Yu, NSLS-II senior accelerator physicist and co-author of the study.

To achieve its improved resolution, the team developed a different method of focusing the electron beam. Instead of using a conventional approach that involves solenoid magnets, the researchers used two groups of four quadrupole magnets to tune the electron beam. Compared to solenoid magnets, which act as just one lens to shape the beam, the quadrupole magnets work like a specialized lens system for the electrons, and they gave the scientists far more flexibility to tune and shape the beam according to the needs of their experiment.

“Our lens system can provide a wide range of tunability of the beam. We can optimize the most important parameters such as beam size, or charge density, and beam divergence based on the experimental conditions, and therefore provide the best beam quality for the scientific needs,” said Yang.

The team can even adjust the parameters on-the-fly with online optimization tools and correct any nonuniformities of the beam shape; however, to make this measurement possible, the team needed the excellent electron beam that ATF provides. ATF has an electron gun that generates an extremely bright and ultrashort electron beam, which offers the best conditions for electron diffraction.

“The team used a photocathode gun that generates the electrons through a process called photoemission,” said Mikhail Fedurin, an accelerator physicist at ATF. “We shoot an ultrashort laser pulse into a copper cathode, and when the pulse hits the cathode a cloud of electrons forms over the copper. We pull the electrons away using an electric field and then accelerate them. The amount of electrons in one of these pulses and our capability to accelerate them to specific energies make our system attractive for material science research – particularly for ultrafast electron diffraction.”

The focusing system together with the ATF electron beam is very sensitive, so the researchers can measure the influences of Earth’ magnetic field on the electron beam.

“In general, electrons are always influenced by magnetic fields—this is how we steer them in particle accelerators in the first place; however, the effect of Earth’s magnetic field is not negligible for the low-energy beam we used in this experiment,” said Victor Smalyuk, NSLS-II accelerator physics group leader and co-author of the study. “The beam deviated from the desired trajectory, which created difficulties during the initial starting phase, so we had to correct for this effect.”

Beyond the high brightness of the electron beam and the high precision of the focusing system, the team also needed the right sample to make these measurements. The CMPMS group provided the team with a polycrystalline gold film to fully explore the newly designed lens system and to put it to the test.

“We made the sample by depositing the gold atoms on a several nanometer thick carbon film using a technique called thermal evaporation,” said Junjie Li, a physicist in the CMPMS department. “We evaporated gold particles so that they condense on the carbon film and form tiny, isolated nanoparticles that slowly merge together and form the polycrystalline film.”

This film was essential for the measurements because it has randomly oriented crystals that merge together. Therefore, the inner structure of the sample is not uniform, but consists of many differently oriented areas, which means that the diffraction pattern mainly depends on the electron beam qualities. This gives the scientists the best ground to really test their lens system, to tune the beam, and to see the impact of their tuning directly in the quality of the diffraction measurement.

“We initially set out to improve electron diffraction for scientific studies of materials, but we also found that this technique can help us characterize our electron beam. In fact, diffraction is very sensitive to the electron beam parameters, so we can use the diffraction pattern of a known sample to measure our beam parameters precisely and directly, which is usually not that easy,” said Yang.

The team intends to pursue further improvements, and they already have plans to develop another setup for ultra-fast electron microscopy to directly visualize a biological sample.

“We hope to achieve ultrafast single-shot electron beam imaging at some point and maybe even make molecular movies, which isn’t possible with our current electron beam imaging setup,” said Yang.

This research was supported by Laboratory Directed Research and Development funding and by DOE’s Office of Science through its support of the ATF.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

BNL Center for Functional Nanomaterials

BNL NSLS-II

BNL NSLS II

BNL RHIC Campus

BNL/RHIC Star Detector

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 Brookhaven National Lab: “Building a Printing Press for New Quantum Materials”

From Brookhaven National Lab

April 22, 2019
Ariana Tantillo
atantillo@bnl.gov

Scientists at Brookhaven Lab’s Center for Functional Nanomaterials are developing an automated system to synthesize entirely new materials made from stacked atomically thin two-dimensional sheets and to characterize their exotic quantum properties.

BNL Center for Functional Nanomaterials

Scientists at Brookhaven Lab’s Center for Functional Nanomaterials are building a robotic system to enable the design, synthesis, and testing of quantum materials, which exhibit unique properties. From left to right: Gregory Doerk, Jerzy Sadowski, Kevin Yager, Young Jae Shin, and Aaron Stein.

Checking out a stack of books from the library is as simple as searching the library’s catalog and using unique call numbers to pull each book from their shelf locations. Using a similar principle, scientists at the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory—are teaming with Harvard University and the Massachusetts Institute of Technology (MIT) to create a first-of-its-kind automated system to catalog atomically thin two-dimensional (2-D) materials and stack them into layered structures. Called the Quantum Material Press, or QPress, this system will accelerate the discovery of next-generation materials for the emerging field of quantum information science (QIS).

Structures obtained by stacking single atomic layers (“flakes”) peeled from different parent bulk crystals are of interest because of the exotic electronic, magnetic, and optical properties that emerge at such small (quantum) size scales. However, flake exfoliation is currently a manual process that yields a variety of flake sizes, shapes, orientations, and number of layers. Scientists use optical microscopes at high magnification to manually hunt through thousands of flakes to find the desired ones, and this search can sometimes take days or even a week, and is prone to human error.

Once high-quality 2-D flakes from different crystals have been located and their properties characterized, they can be assembled in the desired order to create the layered structures. Stacking is very time-intensive, often taking longer than a month to assemble a single layered structure. To determine whether the generated structures are optimal for QIS applications—ranging from computing and encryption to sensing and communications—scientists then need to characterize the structures’ properties.

“In talking to our university collaborators at Harvard and MIT who synthesize and study these layered heterostructures, we learned that while bits of automation exist—such as software to locate the flakes and joysticks to manipulate the flakes—there is no fully automated solution,” said CFN Director Charles Black, the administrative lead on the QPress project.

The idea for the QPress was conceived in early 2018 by Professor Amir Yacoby of the Department of Physics at Harvard. The concept was then refined through a collaboration between Yacoby; Black and Kevin Yager, leader of the CFN Electronic Nanomaterials Group; Philip Kim, also of Harvard’s Department of Physics; and Pablo Jarillo-Herrero and Joseph Checkelsky, both of the Department of Physics at MIT.

According to Black, the unique CFN role was clear: “We realized that building a robot that can enable the design, synthesis, and testing of quantum materials is extremely well-matched to the skills and expertise of scientists at the CFN. As a user facility, CFN is meant to be a resource for the scientific community, and QIS is one of our growth areas for which we’re expanding our capabilities, scientific programs, and staff.”

Graphene sparks 2-D materials research

The interest in 2-D materials dates back to 2004, when scientists at the University of Manchester isolated the world’s first 2-D material, graphene—a single layer of carbon atoms. They used a surprisingly basic technique in which they placed a piece of graphite (the core material of pencils) on Scotch tape, repeatedly folding the tape in half and peeling it apart to extract ever-thinner flakes. Then, they rubbed the tape on a flat surface to transfer the flakes. Under an optical microscope, the one-atom-thick flakes can be located by their reflectivity, appearing as very faint spots. Recognized with a Nobel Prize in 2010, the discovery of graphene and its unusual properties—including its remarkable mechanical strength and electrical and thermal conductivity—has prompted scientists to explore other 2-D materials.

Many labs continue to use this laborious approach to make and find 2-D flakes. While the approach has enabled scientists to perform various measurements on graphene, hundreds of other crystals—including magnets, superconductors, and semiconductors—can be exfoliated in the same way as graphite. Moreover, different 2-D flakes can be stacked to build materials that have never existed before. Scientists have very recently discovered that the properties of these stacked structures depend not only on the order of the layers but also on the relative angle between the atoms in the layers. For example, a material can be tuned from a metallic to an insulating state simply by controlling this angle. Given the wide variety of samples that scientists would like to explore and the error-prone and time-consuming nature of manual synthesis methods, automated approaches are greatly needed.

“Ultimately, we would like to develop a robot that delivers a stacked structure based on the 2-D flake sequences and crystal orientations that scientists select through a web interface to the machine,” said Black. “If successful, the QPress would enable scientists to spend their time and energy studying materials, rather than making them.”

A modular approach

In September 2018, further development of the QPress was awarded funding by the DOE, with a two-part approach. One award was for QPress hardware development at Brookhaven, led by Black; Yager; CFN scientists Gregory Doerk, Aaron Stein, and Jerzy Sadowski; and CFN scientific associate Young Jae Shin. The other award was for a coordinated research project led by Yacoby, Kim, Jarillo-Herrero, and Checkelsky. The Harvard and MIT physicists will use the QPress to study exotic forms of superconductivity—the ability of certain materials to conduct electricity without energy loss at very low temperatures—that exist at the interface between a superconductor and magnet. Some scientists believe that such exotic states of matter are key to advancing quantum computing, which is expected to surpass the capabilities of even today’s most powerful supercomputing.

A photo of the prototype exfoliator. The robotic system transfers peeled 2-D flakes from the parent crystal to a substrate. The exfoliator allows scientists to control stamping pressure, pressing time, number of repeated presses, angle of pressing, and lateral force applied during transfer, for improved repeatability.

A fully integrated automated machine consisting of an exfoliator, a cataloger, a library, a stacker, and a characterizer is expected in three years. However, these modules will come online in stages to enable the use of QPress early on.

The team has already made some progress. They built a prototype exfoliator that mimics the action of a human peeling flakes from a graphite crystal. The exfoliator presses a polymer stamp into a bulk parent crystal and transfers the exfoliated flakes by pressing them onto a substrate. In their first set of experiments, the team investigated how changing various parameters—stamping pressure, pressing time, number of repeated presses, angle of pressing, and lateral force applied during transfer—impact the process.

“One of the advantages of using a robot is that, unlike a human, it reproduces the same motions every time, and we can optimize these motions to generate lots of very thin large flakes,” explained Yager. “Thus, the exfoliator will improve both the quality and quantity of 2-D flakes peeled from parent crystals by refining the speed, precision, and repeatability of the process.”

In collaboration with Stony Brook University assistant professor Minh Hoai Nguyen of the Department of Computer Science and PhD student Boyu Wang of the Computer Vision Lab, the scientists are also building a flake cataloger. Through image-analysis software, the cataloger scans a substrate and records the locations of exfoliated flakes and their properties.

“The flakes that scientists are interested in are thin and thus faint, so manual visual inspection is a laborious and error-prone process,” said Nguyen. “We are using state-of-the-art computer vision and deep learning techniques to develop software that can automate this process with higher accuracy.”

A schematic showing the workflow for cataloging flake locations and properties. Image grids of exfoliated samples are automatically analyzed, with each flake tracked individually so that scientists can locate any desired flake on a sample.

“Our collaborators have said that a system capable of mapping their sample of flakes and showing them where the “good” flakes are located—as determined by parameters they define—would be immensely helpful for them,” said Yager. “We now have this capability and would like to put it to use.”

Eventually, the team plans to store a large set of different catalogued flakes on shelves, similar to books in a library. Scientists could then access this materials library to select the flakes they want to use, and the QPress would retrieve them.

According to Black, the biggest challenge will be the construction of the stacker—the module that retrieves samples from the library, “drives” to the locations where the selected flakes reside, and picks the flakes up and places them in a repetitive process to build stacks according to the assembly instructions that scientists program into the machine. Ultimately, the scientists would like the stacker to assemble the layered structures not only faster but also more accurately than manual methods.

The QPress will have five modules when completed: an exfoliator, a cataloger, a materials library, a stacker, and a characterizer/fabricator.

The final module of the robot will be a material characterizer, which will provide real-time feedback throughout the entire synthesis process. For example, the characterizer will identify the crystal structure and orientation of exfoliated flakes and layered structures through low-energy electron diffraction (LEED)—a technique in which a beam of low-energy electrons is directed toward the surface of a sample to produce a diffraction pattern characteristic of the surface geometry.

“There are many steps to delivering a fully automated solution,” said Black. “We intend to implement QPress capabilities as they become available to maximize benefit to the QIS community.”

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

BNL Center for Functional Nanomaterials

BNL NSLS-II

BNL NSLS II

BNL RHIC Campus

BNL/RHIC Star Detector

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 Lawrence Berkeley National Lab: “Electric Skyrmions Charge Ahead for Next-Generation Data Storage”

From Lawrence Berkeley National Lab

April 18, 2019
Theresa Duque
tnduque@lbl.gov
(510) 495-2418

Berkeley Lab-led research team makes a chiral skyrmion crystal with electric properties; puts new spin on future information storage applications.

VIDEO: Simulation of a single polar skyrmion. Red arrows signify that this is a left-handed skyrmion. The other arrows represent the angular distribution of the dipoles. (Credit: Xiaoxing Cheng, Pennsylvania State University; C.T. Nelson, Oak Ridge National Laboratory; and Ramamoorthy Ramesh, Berkeley Lab)

When you toss a ball, what hand do you use? Left-handed people naturally throw with their left hand, and right-handed people with their right. This natural preference for one side versus the other is called handedness, and can be seen almost everywhere – from a glucose molecule whose atomic structure leans left, to a dog who shakes “hands” only with her right.

Handedness can be exhibited in chirality – where two objects, like a pair of gloves, can be mirror images of each other but cannot be superimposed on one another. Now a team of researchers led by Berkeley Lab has observed chirality for the first time in polar skyrmions – quasiparticles akin to tiny magnetic swirls – in a material with reversible electrical properties. The combination of polar skyrmions and these electrical properties could one day lead to applications such as more powerful data storage devices that continue to hold information – even after a device has been powered off. Their findings were reported this week in the journal Nature.

“What we discovered is just mind-boggling,” said Ramamoorthy Ramesh, who holds appointments as a faculty senior scientist in Berkeley Lab’s Materials Sciences Division and as the Purnendu Chatterjee Endowed Chair in Energy Technologies in Materials Science and Engineering and Physics at UC Berkeley. “We hadn’t planned on making skyrmions. So for us to end up making a chiral skyrmion is exciting.”

When the team of researchers – co-led by Ramesh and Lane Martin, a staff scientist in Berkeley Lab’s Materials Sciences Division and a professor in Materials Science and Engineering at UC Berkeley – began this study in 2016, they had set out to find ways to control how heat moves through materials. So they fabricated a special crystal structure called a superlattice from alternating layers of lead titanate (an electrically polar material, whereby one end is positively charged and the opposite end is negatively charged) and strontium titanate (an insulator, or a material that doesn’t conduct electric current).

But once they took STEM (scanning transmission electron microscopy) measurements of the lead titanate/strontium titanate superlattice at the Molecular Foundry, a U.S. DOE Office of Science User Facility at Berkeley Lab that specializes in nanoscale science, they saw something strange that had nothing to do with heat: Bubble-like formations had cropped up all across the device.

Bubbles, bubbles everywhere

So what were these “bubbles,” and how did they get there?

Those bubbles, it turns out, were polar skyrmions – or textures made up of opposite electric charges known as dipoles. Researchers had always assumed that skyrmions would only appear in magnetic materials, where special interactions between magnetic spins of charged electrons stabilize the twisting chiral patterns of skyrmions. So when the Berkeley Lab-led team of researchers discovered skyrmions in an electric material, they were astounded.

Simulation of the cross-section in the middle of the polar-skyrmion bubble. (Credit: Berkeley Lab)

Through the researchers’ collaboration with theorists Javier Junquera of the University of Cantabria in Spain, and Jorge Íñiguez of the Luxembourg Institute of Science and Technology, they discovered that these textures had a unique feature called a “Bloch component” that determined the direction of its spin, which Ramesh compares to the fastening of a belt – where if you’re left-handed, the belt goes from left to right. “And it turned out that this Bloch component – the skyrmion’s equatorial belt, so to speak – is the key to its chirality or handedness,” he said.

While using sophisticated STEM at Berkeley Lab’s Molecular Foundry and at the Cornell Center for Materials Research, where David Muller of Cornell University took atomic snapshots of skyrmions’ chirality at room temperature in real time, the researchers discovered that the forces placed on the polar lead titanate layer by the nonpolar strontium titanate layer generated the polar skyrmion “bubbles” in the lead titanate.

“Materials are like people,” said Ramesh. “When people get stressed, they respond in unpredictable ways. And that’s what materials do too: In this case, by surrounding lead titanate by strontium titanate, lead titanate starts to go crazy – and one way that it goes crazy is to create polar textures like skyrmions.”

Through the researchers’ collaboration with theorists Javier Junquera of the University of Cantabria in Spain, and Jorge Íñiguez of the Luxembourg Institute of Science and Technology, they discovered that these textures had a unique feature called a “Bloch component” that determined the direction of its spin, which Ramesh compares to the fastening of a belt – where if you’re left-handed, the belt goes from left to right. “And it turned out that this Bloch component – the skyrmion’s equatorial belt, so to speak – is the key to its chirality or handedness,” he said.

While using sophisticated STEM at Berkeley Lab’s Molecular Foundry and at the Cornell Center for Materials Research, where David Muller of Cornell University took atomic snapshots of skyrmions’ chirality at room temperature in real time, the researchers discovered that the forces placed on the polar lead titanate layer by the nonpolar strontium titanate layer generated the polar skyrmion “bubbles” in the lead titanate.

Custom-designed scanning transmission electron microscope at Cornell University by David Muller/Cornell University

LBNL THEMIS scannng transmission electronic micsoscope

“Materials are like people,” said Ramesh. “When people get stressed, they respond in unpredictable ways. And that’s what materials do too: In this case, by surrounding lead titanate by strontium titanate, lead titanate starts to go crazy – and one way that it goes crazy is to create polar textures like skyrmions.”

Shining a light on crystal chirality

To confirm their observations, senior staff scientist Elke Arenholz and staff scientist Padraic Shafer at Berkeley Lab’s Advanced Light Source (ALS), along with Margaret McCarter, a physics Ph.D. student from the Ramesh Lab at UC Berkeley, probed the chirality by using a spectroscopic technique known as RSXD-CD (resonant soft X-ray diffraction circular dichroism), one of the highly optimized tools available to the scientific community at the ALS, a U.S. DOE Office of Science User Facility that specializes in lower energy, “soft” X-ray light for studying the properties of materials.

LBNL ALS

Simulations of skyrmion bubbles and elongated skyrmions for the lead titanate/strontium titanate superlattice. (Credit: Berkeley Lab)

Light waves can be “circularly polarized” to also have handedness, so the researchers theorized that if polar skyrmions have handedness, a left-handed skyrmion, for example, should interact more strongly with left-handed, circularly polarized light – an effect known as circular dichroism.

When McCarter and Shafer tested the samples at the ALS, they successfully uncovered another piece to the chiral skyrmion puzzle – they found that incoming circularly polarized X-rays, like a screw whose threads rotate either clockwise or counterclockwise, interact with skyrmions whose dipoles rotate in the same direction, even at room temperature. In other words, they found evidence of circular dichroism – where there is only a strong interaction between X-rays and polar skyrmions with the same handedness.

“The theoretical simulations and microscopy both revealed the presence of a Bloch component, but to confirm the chiral nature of these skyrmions, the last piece of the puzzle was really the circular dichroism measurements,” McCarter said. “It is amazing to observe this effect in materials that typically don’t have handedness. We are excited to explore the implications of this chirality in a ferroelectric and how it can be controlled in a way that could be useful for storing data.”

Now that the researchers have made a single electric skyrmion and confirmed its chirality, they plan to make an array of dozens of electric skyrmions – each one with a diameter of just 8 nm (for comparison, the Ebola virus is about 50 nm wide) – with the same handedness. “In terms of applications, this is exciting because now we have chirality – switching a skyrmion on or off, or between left-handed and right-handed – on top of still being able to use the charge for storing data,” Ramesh said.

The researchers next plan to study the effects of applying an electric field on the polar skyrmions. “Now that we know that polar/electric skyrmions are chiral, we want to see if we can electrically manipulate them. If I apply an electric field, can I turn each one like a turnstile? Can I move each one, one at a time, like a checker on a checkerboard? If we can somehow move them, write them, and erase them for data storage, then that would be an amazing new technology,” Ramesh said.

Also contributing to the study were researchers from Pennsylvania State University, Cornell University, and Oak Ridge National Laboratory.

The work was supported by the DOE Office of Science with additional funding provided by the Gordon and Betty Moore Foundation’s EPiQS Initiative, the National Science Foundation, the Luxembourg National Research Fund, and the Spanish Ministry of Economy and Competitiveness.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Bringing Science Solutions to the World

In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

A U.S. Department of Energy National Laboratory Operated by the University of California.

From Michigan Technical University: “It’s Hip to be Square (And Lighter Than Air)”

From Michigan Technical University

April 10, 2019

Kelley Christensen
kelleyc@mtu.edu
906-487-3510

(Left) Atomic resolution STEM image along with element maps in false color. Green and red represent Sc and Al atoms, respectively. At the right corner, Al and Sc maps are super imposed. (Right) A cropped part from the super imposed map (ROI-1) show a unit cell of Al-Sc alloy. An arrow shows migration of Sc atom to Al site.

There’s a method to my atomic-resolution imaging.

Aluminum is used in many applications calling for a light-weight metal. Combine aluminum with scandium, a rare-earth metal nearly as low-density as aluminum, but with a smaller diffusion rate (the rate at which molecules move through the metals, which is greatly affected by temperature), and the resulting alloy is able to withstand greater heat and has greater tensile strength. Useful for manufacturing airplanes, bicycles, firearms, and in the future, automobiles.

Does the way scandium bonds to aluminum affect alloy strength? To figure it out, researchers at Michigan Technological University use a variety of methods to understand what’s happening at the atomic level.

Paul Sanders, Patrick Horvath Endowed Associate Professor of materials science and engineering, and materials science and engineering graduate student Yang Yang, are trying to strengthen aluminum by adding scandium to it. Yang prepares the alloy samples by rapid solidification. He rapidly cools a soup of aluminum and scandium metals by dropping a small amount of liquid metal on a rotating wheel, which forces the droplet to become a ribbon as it cools to form the alloy.

In its parent form, aluminum has a face-centered cubic crystal structure, which means the aluminum atoms are located at the corners and at the faces of a cube. Where do the scandium atoms bond with the aluminum crystal structure? Sanders and Yang used atomic resolution energy dispersive X-ray spectroscopy (EDS) mapping to determine the location of scandium atoms in the aluminum matrix.

Scientists call analytical electron microscopes “labs-in-a-machine”; in addition to imaging at atomic resolution, the microscopes provide chemical composition information of the sample. Not only can a person see how the atoms are arranged in a sample, it’s easy to determine which elements are present in it.

How does EDS work? When the high-energy electrons used for imaging in the microscopes collide with the atoms in the sample, X-rays are emitted from the sample. These X-rays carry the signatures of the elements present in the sample. The researchers use detectors to collect these characteristics X-rays.

The aberration-corrected FEI Titan Themis scanning transmission electron microscope (STEM) in Michigan Tech’s Applied Chemical and Morphological Analysis Laboratory, makes an electron beam less than an atom in width.

FEI Titan Themis scanning transmission electron microscope (STEM)

This allows researchers to scan through samples one atom column at a time. Additionally, the lab has a SuperXTM X-ray detector [no image available], which is an array of four detectors to collect four times more X-rays than a conventional detector.

Combining the two techniques, researchers can element map at atomic resolution.

The element map shows that the scandium atoms are moving to the corner positions in a cubic crystal structure while aluminum atoms are occupying the faces of the cube. This is what’s known as a chemically ordered L1^2 structure. Interestingly, in one out of eight cases, researchers have found some scandium atoms in the aluminum sites. This occurs when these alloys are rapidly solidified.

These methods are powerful enough to locate a single arrested scandium atom in an aluminum site.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Michigan Technological University (http://www.mtu.edu) is a leading public research university developing new technologies and preparing students to create the future for a prosperous and sustainable world. Michigan Tech offers more than 130 undergraduate and graduate degree programs in engineering; forest resources; computing; technology; business; economics; natural, physical and environmental sciences; arts; humanities; and social sciences.
The College of Sciences and Arts (CSA) fills one of the most important roles on the Michigan Tech campus. We play a part in the education of every student who comes through our doors. We take pride in offering essential foundational courses in the natural sciences and mathematics, as well as the social sciences and humanities—courses that underpin every major on campus. With twelve departments, 28 majors, 30-or-so specializations, and more than 50 minors, CSA has carefully developed programs to suit many interests and skill sets. From sound design and audio technology to actuarial science, applied cognitive science and human factors to rhetoric and technical communication, the college offers many unique programs.

From Brookhaven National Lab: “Putting a New Spin on Majorana Fermions”

From Brookhaven National Lab

April 1, 2019
Ariana Tantillo
atantillo@bnl.gov
(631) 344-2347

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

Split electrons that emerge at the boundaries between different magnetic states in materials known as spin ladders could act as stable bits of information in next-generation quantum computers.

Theoretical calculations performed by (left to right) Neil Robinson, Robert Konik, Alexei Tsvelik, and Andreas Weichselbaum of Brookhaven Lab’s Condensed Matter Physics and Materials Science Department suggest that Majorana fermions exist in the boundaries of magnetic materials with different magnetic phases. Majorana fermions are particle-like excitations that emerge when single electrons fractionalize into two halves, and their unique properties are of interest for quantum applications.

The combination of different phases of water—solid ice, liquid water, and water vapor—would require some effort to achieve experimentally. For instance, if you wanted to place ice next to vapor, you would have to continuously chill the water to maintain the solid phase while heating it to maintain the gas phase.

For condensed matter physicists, this ability to create different conditions in the same system is desirable because interesting phenomena and properties often emerge at the interfaces between two phases. Of current interest is the conditions under which Majorana fermions might appear near these boundaries.

Majorana fermions are particle-like excitations called quasiparticles that emerge as a result of the fractionalization (splitting) of individual electrons into two halves. In other words, an electron becomes an entangled (linked) pair of two Majorana quasiparticles, with the link persisting regardless of the distance between them. Scientists hope to use Majorana fermions that are physically separated in a material to reliably store information in the form of qubits, the building blocks of quantum computers. The exotic properties of Majoranas—including their high insensitivity to electromagnetic fields and other environmental “noise”—make them ideal candidates for carrying information over long distances without loss.

However, to date, Majorana fermions have only been realized in materials at extreme conditions, including at frigid temperatures close to absolute zero (−459 degrees Fahrenheit) and under high magnetic fields. And though they are “topologically” protected from local atomic impurities, disorder, and defects that are present in all materials (i.e., their spatial properties remain the same even if the material is bent, twisted, stretched, or otherwise distorted), they do not survive under strong perturbations. In addition, the range of temperatures over which they can operate is very narrow. For these reasons, Majorana fermions are not yet ready for practical technological application.

Now, a team of physicists led by the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and including collaborators from China, Germany, and the Netherlands has proposed a novel theoretical method for producing more robust Majorana fermions. According to their calculations, as described in a paper published on Jan. 15 in Physical Review Letters, these Majoranas emerge at higher temperatures (by many orders of magnitude) and are largely unaffected by disorder and noise. Even though they are not topologically protected, they can persist if the perturbations change slowly from one point to another in space.

“Our numerical and analytical calculations provide evidence that Majorana fermions exist in the boundaries of magnetic materials with different magnetic phases, or directions of electron spins, positioned next to one other,” said co-author Alexei Tsvelik, senior scientist and leader of the Condensed Matter Theory Group in Brookhaven Lab’s Condensed Matter Physics and Materials Science (CMPMS) Department. “We also determined the number of Majorana fermions you should expect to get if you combine certain magnetic phases.”

For their theoretical study, the scientists focused on magnetic materials called spin ladders, which are crystals formed of atoms with a three-dimensional (3-D) structure subdivided into pairs of chains that look like ladders. Though the scientists have been studying the properties of spin ladder systems for many years and expected that they would produce Majorana fermions, they did not know how many. To perform their calculations, they applied the mathematical framework of quantum field theory for describing the fundamental physics of elementary particles, and a numerical method (density-matrix renormalization group) for simulating quantum systems whose electrons behave in a strongly correlated way.

“We were surprised to learn that for certain configurations of magnetic phases we can generate more than one Majorana fermion at each boundary,” said co-author and CMPMS Department Chair Robert Konik.

For Majorana fermions to be practically useful in quantum computing, they need to be generated in large numbers. Computing experts believe that the minimum threshold at which quantum computers will be able to solve problems that classical computers cannot is 100 qubits. The Majorana fermions also have to be moveable in such a way that they can become entangled.

The team plans to follow up their theoretical study with experiments using engineered systems such as quantum dots (nanosized semiconducting particles) or trapped (confined) ions. Compared to the properties of real materials, those of engineered ones can be more easily tuned and manipulated to introduce the different phase boundaries where Majorana fermions may emerge.

“What the next generation of quantum computers will be made of is unclear right now,” said Konik. “We’re trying to find better alternatives to the low-temperature superconductors of the current generation, similar to how silicon replaced germanium in transistors. We’re in such early stages that we need to explore every possibility available.”

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

BNL NSLS-II

BNL NSLS II

BNL RHIC Campus

BNL/RHIC Star Detector

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 MIT News: “Researchers tune material’s color and thermal properties separately”

From MIT News

April 2, 2019
Jennifer Chu

The visual and thermal properties of polyethylene can be tweaked to produce colorful films with a wide range of heat-radiating capabilities. Image: Felice Frankel

Polymers could be designed to reflect or trap heat, regardless of hue.

The color of a material can often tell you something about how it handles heat. Think of wearing a black shirt on a sweltering summer’s day — the darker the pigment, the warmer you’re likely to feel. Likewise, the more transparent a glass window, the more heat it can let through. A material’s responses to visible and infrared radiation are often naturally linked.

Now MIT engineers have made samples of strong, tissue-like polymer material, the color and heat properties of which they can tailor independently of the other. For instance, they have fabricated samples of very thin black film designed to reflect heat and stay cool. They’ve also made films exhibiting a rainbow of other colors, each made to reflect or absorb infrared radiation regardless of the way they respond to visible light.

The researchers can specifically tune the color and heat properties of this new material to fit the requirements for a host of wide-ranging applications, including colorful, heat-reflecting building facades, windows, and roofs; light-absorbing, heat-dissipating covers for solar panels; and lightweight fabric for clothing, outerwear, tents, and backpacks — all designed to either trap or reflect heat, depending on the environments in which they would be used.

“With this material, everything could look more colorful, because then you wouldn’t be concerned with what color does to the thermal balance of, say, a building, or a window, or your clothing,” says Svetlana Boriskina, a research scientist in MIT’s Department of Mechanical Engineering.

Boriskina is author of a study that appears today in the journal Optical Materials Express, outlining the new material-engineering technique. Her MIT co-authors are Luis Marcelo Lozano, Seongdon Hong, Yi Huang, Hadi Zandavi, Yoichiro Tsurimaki, Jiawei Zhou, Yanfei Xu, and Gang Chen, the Carl Richard Soderberg Professor of Power Engineering, along with Yassine Ait El Aoud and Richard Osgood III, both of the Combat Capabilities Development Command Soldier Center, in Natick, Massachusetts.

Polymer conductors

For this work, Boriskina was inspired by the vibrant colors in stained-glass windows, which for centuries have been made by adding particles of metals and other natural pigments to glass.

“However, despite providing excellent visual transparency, glass has many limitations as a material,” Boriskina notes. “It is bulky, inflexible, fragile, does not spread heat well, and is obviously not suitable for wearable applications.”

She says that while it’s relatively simple to tailor the color of glass, the material’s response to heat is difficult to tune. For instance, glass panels reflect room-temperature heat and trap it inside the room. Furthermore, if colored glass is exposed to incoming sunlight from a particular direction, the heat from the sun can create a hotspot, which is difficult to dissipate in glass. If a material like glass can’t conduct or dissipate heat well, that heat could damage the material.

The same can be said for most plastics, which can be engineered in any color but for the most part are thermal absorbers and insulators, concentrating and trapping heat rather than reflecting it away.

For the past several years, Chen’s lab has been looking into ways to manipulate flexible, lightweight polymer materials to conduct, rather than insulate, heat, mostly for applications in electronics. In previous work, the researchers found that by carefully stretching polymers like polyethylene, they could change the material’s internal structure in a way that also changed its heat-conducting properties.

Boriskina thought this technique might be useful not just for fabricating polymer-based electronics, but also in architecture and apparel. She adapted this polymer-fabrication technique, adding a twist of color.

“It’s very hard to develop a new material with all these different properties in it,” she says. “Usually if you tune one property, the other gets destroyed. Here, we started with one property that was discovered in this group, and then we added a new property creatively. All together it works as a multifunctional material.”

Hotspots stretched away

To fabricate the colorful films, the team started with a mixture of polyethylene powder and a chemical solvent, to which they added certain nanoparticles to give the film a desired color. For instance, to make black film, they added particles of silicon; other red, blue, green, and yellow films were made with the addition of various commercial dyes.

The team then attached each nanoparticle-embedded film onto a roll-to-roll apparatus, which they heated up to soften the film, making it more pliable as the researchers carefully stretched the material.

As they stretched each film, they found, unsurprisingly, that the material became more transparent. They also observed that polyethylene’s microscopic structure changed as it stretched. Where normally the material’s polymer chains resemble a disorganized tangle, similar to cooked spaghetti, when stretched these chains straighten out, forming parallel fibers.

When the researchers placed each sample under a solar simulator — a lamp that mimics the visible and thermal radiation of the sun — they found the more stretched out a film, the more heat it was able to dissipate. The long, parallel polymer chains essentially provided a direct route along which heat could travel. Along these chains, heat, in the form of phonons, could then shoot away from its source, in a “ballistic” fashion, avoiding the formation of hotspots.

The researchers also found that the less they stretched the material, the more insulating it was, trapping heat, and forming hotspots within polymer tangles.

By controlling the degree to which the material is stretched, Boriskina could control polyethylene’s heat-conducting properties, regardless of the material’s color. She also carefully chose the nanoparticles, not just by their visual color, but also by their interactions with invisible radiative heat. She says researchers can potentially use this technique to produce thin, flexible, colorful polymer films, that can conduct or insulate heat, depending on the application.

Going forward, she plans to launch a website that offers algorithms to calculate a material’s color and thermal properties, based on its dimensions and internal structure.

In addition to films, her group is now working on fabricating nanoparticle-embedded polyethylene thread, which can be stitched together to form lightweight apparel, designed to be either insulating, or cooling.

“This is in film factor now, but we’re working it into fibers and fabrics,” Boriskina says. “Polyethylene is produced by the billions of tons and could be recycled, too. I don’t see any significant impediments to large-scale production.”

This research was supported, in part, by the Combat Capabilities Development Command Soldier Center.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

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.

From Lawrence Berkeley National Lab: “Scientists Take a Deep Dive Into the Imperfect World of 2D Materials”

From Lawrence Berkeley National Lab

March 8, 2019

Glenn Roberts Jr.
geroberts@lbl.gov
(510) 486-5582

Berkeley Lab-led team combines several nanoscale techniques to gain new insights on the effects of defects in a well-studied monolayer material.

This animation displays a scan of arrow-shaped flakes of a 2D material. Samples were scanned across their electron energy, momentum, and horizontal and vertical coordinates using an X-ray-based technique known as nanoARPES at Berkeley Lab’s Advanced Light Source. Red represents the highest intensity measured, followed by orange, yellow, green, and blue, and purple (least intense). (Credit: Roland Koch/Berkeley Lab)

Nothing is perfect, or so the saying goes, and that’s not always a bad thing. In a study at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), scientists learned how nanoscale defects can enhance the properties of an ultrathin, so-called 2D material.

They combined a toolbox of techniques to home in on natural, nanoscale defects formed in the manufacture of tiny flakes of a monolayer material known as tungsten disulfide (WS2) and measured their electronic effects in detail not possible before.

“Usually we say that defects are bad for a material,” said Christoph Kastl, a postdoctoral researcher at Berkeley Lab’s Molecular Foundry and the lead author of the study, published in the journal ACS Nano. “Here they provide functionality.”

Tungsten disulfide is a well-studied 2D material that, like other 2D materials of its kind, exhibits special properties because of its atomic thinness. It is particularly well-known for its efficiency in absorbing and emitting light, and it is a semiconductor.

Members of this family of 2D materials could serve as high-efficiency computer transistors and as other electronics components, and they also are prime candidates for use in ultrathin, high-efficiency solar cells and LED lighting, as well as in quantum computers.

These 2D materials could also be incorporated in new forms of memory storage and data transfer, such as spintronics and valleytronics, that would revolutionize electronics by making use of materials in new ways to make smaller and more efficient devices.

The latest result marks the first comprehensive study at the Lab’s Advanced Light Source (ALS) involving a technique called nanoARPES, which researchers enlisted to probe the 2D samples with X-rays.

LBL ALS

The X-rays knocked out electrons in the sample, allowing researchers to measure their direction and energy. This revealed nanoscale defects and how the electrons interact with each other.

The nanoARPES capability is housed in an X-ray beamline, launched in 2016, known as MAESTRO (Microscopic and Electronic Structure Observatory). It is one of dozens of specialized beamlines at the ALS, which produces light in different forms – from infrared to X-rays – for a variety of simultaneous experiments.

“It’s a very big advance to get this electronic structure on small length scales,” said Eli Rotenberg, a senior staff scientist at the ALS who was a driving force in developing MAESTRO and served as one of the study’s leaders. “That matters for real devices.”

The team also enlisted a technique known as XPS (X-ray photoelectron spectroscopy) to study the chemical makeup of a sample at very small scales; a form of AFM (atomic force microscopy) to view structural details approaching the atomic scale; and a combined form of optical spectroscopy (Raman/photoluminescence spectroscopy) to study how light interacts with the electrons at microscope scales.

The various techniques were applied at the Molecular Foundry, where the material was synthesized, and at the ALS.

LBNL Molecular Foundry

The sample used in the study contained microscopic, roughly triangular flakes, each measuring about 1 to 5 microns (millionths of a meter) across. They were grown atop titanium dioxide crystals using a conventional layering process known as chemical vapor deposition, and the defects were largely concentrated around the edges of the flakes, a signature of the growth process. Most of the experiments focused on a single flake of tungsten disulfide.

This image shows an illustration of the atomic structure of a 2D material called tungsten disulfide. Tungsten atoms are shown in blue and sulfur atoms are shown in yellow. The background image, taken by an electron microscope at Berkeley Lab’s Molecular Foundry, shows groupings of flakes of the material (dark gray) grown by a process called chemical vapor deposition on a titanium dioxide layer (light gray). (Credit: Katherine Cochrane/Berkeley Lab)

Adam Schwartzberg, a staff scientist at the Molecular Foundry who served as a co-lead in the study, said, “It took a combination of multiple types of techniques to pin down what’s really going on.”

He added, “Now that we know what defects we have and what effect they have on the properties of the material, we can use this information to reduce or eliminate defects – or if you want the defect, it gives us a way of knowing where the defects are,” and provides fresh insight about how to propagate and amplify the defects in the sample-production process.

While the concentration of edge defects in the WS2 flakes was generally known before the latest study, Schwartzberg said that their effects on materials performance hadn’t previously been studied in such a comprehensive and detailed way.

Researchers learned that a 10 percent deficiency in sulfur atoms was associated with the defective edge regions of the samples compared to other regions, and they identified a slighter, 3 percent sulfur deficiency toward the center of the flakes. Researchers also noted a change in the electronic structure and higher abundance of freely moving electrical charge-carriers associated with the high-defect edge areas.

This sequence of images shows a variety of energy intensities (white and yellow) at the edges of a 2D material known as tungsten disulfide, as measured via different techniques: photoluminescense intensity (far left); contact potential difference map (second from left); exciton emission intensity (third from left) – excitons are pairs consistent of an electrons and their quasiparticle counterpart, called a hole; trion emission intensity (far right) – trions are gropus of three charged quasiparticles consistening of either two electrons and a hole or two holes and an electron). (Credit: Christoph Kastl/Berkeley Lab)

For this study, the defects were due to the sample-growth process. Future nanoARPES studies will focus on samples with defects that are induced through chemical processing or other treatments. Researchers hope to control the amount and kinds of atoms that are affected, and the locations where these defects are concentrated in the flakes.

Such tiny tweaks could be important for processes like catalysis, which is used to enhance and accelerate many important industrial chemical production processes, and to explore quantum processes that rely on the production of individual particles that serve as information carriers in electronics.

Because research of WS2 and related 2D materials is still in its infancy, there are many unknowns about the roles specific types of defects play in these materials, and Rotenberg noted that there is a world of possibilities for so-called “defect engineering” in these materials.

In addition, MAESTRO’s nanoARPES has the ability to study the electronic structures of stacks of different types of 2D material layers. This can help researchers understand how their properties depend on their physical arrangement, and to explore working devices that incorporate 2D materials.

“The unprecedented small scale of the measurements – currently approaching 50 nanometers – makes nanoARPES a great discovery tool that will be particularly useful to understand new materials as they are invented,” Rotenberg said.

MAESTRO is one of the priority beamlines to be upgraded as part of the Lab’s ALS Upgrade (ALS-U) project, a major undertaking that will produce even brighter, more focused beams of light for experiments. “The ALS-U project will further improve the performance of the nanoARPES technique,” Rotenberg said, “making its measurements 10 to 30 times more efficient and significantly improving our ability to reach even shorter length scales.”

NanoARPES could play an important role in the development of new solar technologies, because it allows researchers to see how nanoscale variations in chemical makeup, number of defects, and other structural features affect the electrons that ultimately govern their performance. These same issues are important for many other complex materials, such as superconductors, magnets, and thermoelectrics – which convert temperature to current and vice versa – so nanoARPES will also be very useful for these as well.

The Molecular Foundry and ALS are both DOE Office of Science User Facilities.

Researchers from the Berkeley Lab Chemical Sciences Division, Aarhus University in Denmark, and Montana State University also participated in this study. The work was supported by the U.S. Department of Energy’s Office of Basic Energy Sciences, the DOE Early Career Grant program, Berkeley Lab’s Laboratory Directed Research and Development program, the Villum Foundation, and the German Academic Exchange Service.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Bringing Science Solutions to the World

In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

A U.S. Department of Energy National Laboratory Operated by the University of California.

From Lawrence Berkeley National Lab: “When Semiconductors Stick Together, Materials Go Quantum”

From Lawrence Berkeley National Lab

March 7, 2019
Theresa Duque
tnduque@lbl.gov
(510) 495-2418

A new study led by Berkeley Lab reveals how aligned layers of atomically thin semiconductors can yield an exotic new quantum material.

A method developed by a Berkeley Lab-led research team may one day turn ordinary semiconducting materials into quantum electronic devices. (Credit: iStock.com/NiPlot)

A team of researchers led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a simple method that could turn ordinary semiconducting materials into quantum machines – superthin devices marked by extraordinary electronic behavior. Such an advancement could help to revolutionize a number of industries aiming for energy-efficient electronic systems – and provide a platform for exotic new physics.

The study describing the method, which stacks together 2D layers of tungsten disulfide and tungsten diselenide to create an intricately patterned material, or superlattice, was published online recently in the journal Nature.

“This is an amazing discovery because we didn’t think of these semiconducting materials as strongly interacting,” said Feng Wang, a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and professor of physics at UC Berkeley. “Now this work has brought these seemingly ordinary semiconductors into the quantum materials space.”

The twist angle formed between atomically thin layers of tungsten disulfide and tungsten diselenide acts as a “tuning knob,” transforming these semiconductors into an exotic quantum material. (Credit: Berkeley Lab) (Credit: Berkeley Lab)

Two-dimensional (2D) materials, which are just one atom thick, are like nanosized building blocks that can be stacked arbitrarily to form tiny devices. When the lattices of two 2D materials are similar and well-aligned, a repeating pattern called a moiré superlattice can form.

For the past decade, researchers have been studying ways to combine different 2D materials, often starting with graphene – a material known for its ability to efficiently conduct heat and electricity. Out of this body of work, other researchers had discovered that moiré superlattices formed with graphene exhibit exotic physics such as superconductivity when the layers are aligned at just the right angle.

The new study, led by Wang, used 2D samples of semiconducting materials – tungsten disulfide and tungsten diselenide – to show that the twist angle between layers provides a “tuning knob” to turn a 2D semiconducting system into an exotic quantum material with highly interacting electrons.

Entering a new realm of physics

Co-lead authors Chenhao Jin, a postdoctoral scholar, and Emma Regan, a graduate student researcher, both of whom work under Wang in the Ultrafast Nano-Optics Group at UC Berkeley, fabricated the tungsten disulfide and tungsten diselenide samples using a polymer-based technique to pick up and transfer flakes of the materials, each measuring just tens of microns in diameter, into a stack.

They had fabricated similar samples of the materials for a previous study [Science], but with the two layers stacked at no particular angle. When they measured the optical absorption of a new tungsten disulfide and tungsten diselenide sample for the current study, they were taken completely by surprise.

The absorption of visible light in a tungsten disulfide/tungsten diselenide device is largest when the light has the same energy as the system’s exciton, a quasiparticle that consists of an electron bound to a hole that is common in 2D semiconductors. (In physics, a hole is a currently vacant state that an electron could occupy.)

The large potential energy of three distinct exciton states in a 2D tungsten disulfide/tungsten diselenide device could introduce exotic quantum phenomena into semiconducting materials. (Credit: Berkeley Lab)

For light in the energy range that the researchers were considering, they expected to see one peak in the signal that corresponded to the energy of an exciton.

Instead, they found that the original peak that they expected to see had split into three different peaks representing three distinct exciton states.

What could have increased the number of exciton states in the tungsten disulfide/tungsten diselenide device from one to three? Was it the addition of a moiré superlattice?

To find out, their collaborators Aiming Yan and Alex Zettl used a transmission electron microscope (TEM) at Berkeley Lab’s Molecular Foundry, a nanoscale science research facility, to take atomic-resolution images of the tungsten disulfide/tungsten diselenide device to check how the materials’ lattices were aligned.

The TEM images confirmed what they had suspected all along: the materials had indeed formed a moiré superlattice. “We saw beautiful, repeating patterns over the entire sample,” said Regan. “After comparing this experimental observation with a theoretical model, we found that the moiré pattern introduces a large potential energy periodically over the device and could therefore introduce exotic quantum phenomena.”

The researchers next plan to measure how this new quantum system could be applied to optoelectronics, which relates to the use of light in electronics; valleytronics, a field that could extend the limits of Moore’s law by miniaturizing electronic components; and superconductivity, which would allow electrons to flow in devices with virtually no resistance.

Also contributing to the study were researchers from Arizona State University and the National Institute for Materials Science in Japan.

The work was supported by the DOE Office of Science. Additional funding was provided by the National Science Foundation, the Department of Defense, and the Elemental Strategy Initiative conducted by MEXT, Japan, and JSPS KAKENHI. The Molecular Foundry is a DOE Office of Science user facility.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Bringing Science Solutions to the World

In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

A U.S. Department of Energy National Laboratory Operated by the University of California.