From Fleet ARC Center of Excellence AU via phys.org: “Growing metallic crystals in liquid metal”

From Fleet ARC Center of Excellence AU

via

From phys.org

Experimental set up. Credit: FLEET.

Imagine an alien world with oceans of liquid metal.

If such a world exists, metallic elements are likely the sources of the dissolved materials and particles in these oceans. Everything would be made of metallic elements, even lifeforms.

It may sound like a concept pulled straight out of a science fiction movie, but some basic elements of this fantastical vision can still be easily realized on our planet.

We are all familiar with growing crystals in water. The most obvious example is the growth of sugar crystals that many of us have done during our time at school. Here, sugar solute in a water solvent can precipitate as crystals out of the solution.

Now, Australian researchers have shown the possibility of an analogous observation with liquid metals as a solvent and published an exciting report in the journal ACS Nano.

It is known that metallic elements can dissolve and form solutes in liquid metal solvents. It is also known that these secondary metals can form clusters of metallic crystals inside the metallic solvent. This is in fact the base of the well-established field of metallurgy. However, in metallurgy the primary interest is in solidifying solvents and solutes together to create solid alloys for a variety of applications.

The researchers at at the University of New South Wales (UNSW), School of Chemical Engineering looked at liquid metals from a different angle.

They used gallium, which is liquid at near room temperature, like mercury, and dissolved different metals into it.

Small crystals of these metallic elements formed inside the liquid metal.

However, as the surface tension of liquid metal is quite high, these metallic crystals remained trapped inside the liquid metals.

High surface tension means that liquid metals are immiscible in other liquids and as such it is not possible for the metallic crystals to naturally free themselves into the surrounding.

The researchers discovered a new method to extract these metallic crystals out of the liquid alloy. By applying a voltage to the surface of a liquid metal droplet, they were able to reduce the surface tension sufficiently to allow the metallic crystals to be pulled out.

“We were able to make very small crystals that were of a metallic and metal oxide nature,” said Dr. Mohannad Mayyas, author of the paper. “We dissolved indium, tin, and zinc into gallium liquid and precipitated them out of the media by applying a voltage in a specific set-up. The method is really advantageous as making such crystals generally requires hazardous precursors and harsh synthesis conditions.”

“Other researchers can continue our work and explore the many possibilities that liquid metal solvents offer,” suggested Prof Kourosh Kalantar-Zadeh, the corresponding author of the paper. “For example, liquid metals are super catalytic. While the formation of crystals in aqueous solutions may take a long time, the creation of the metallic elements inside liquid metal can take place instantly. Additionally, liquid metals offer opportunities for intriguing interfacial chemistry that do not exist for any other systems.”

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FLEET addresses a grand challenge: reducing the energy used in information technology, which now accounts for 8% of the electricity use on Earth, and is doubling every 10 years.

The current, silicon-based technology will stop becoming more efficient in the next decade as Moore’s law comes to an end.

FLEET is the ARC Centre of Excellence in Future Low-Energy Electronics Technologies

From Uni Kiel: “Collective quantum effect: When electrons keep together”

From Uni Kiel

9.11.20

Dr. Tobias Dornheim
Center for Advanced Systems Understanding (CASUS)
Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
+49 3581 375 2351
t.dornheim@hzdr.de

Julia Siekmann
Science Communication Officer, Research area Kiel Nano Surface and Interface Sciences
+49 (0)431/880-4855
jsiekmann@uv.uni-kiel.de

Nonlinear reactions of warm dense matter described for the first time.

Simulation of a disturbance of a warm dense matter system by a laser beam. © Jan Vorberger.

Many celestial objects such as stars or planets contain matter that is exposed to high temperatures and pressure – experts call it warm dense matter (WDM). Although this state of matter on earth only occurs in the earth’s core, research on WDM is fundamental for various future areas such as clean energy, harder materials or a better understanding of solar systems. In a study recently published in Physical Review Letters, a team led by physicist Dr. Tobias Dornheim of the Center for Advanced Systems Understanding (CASUS) at Helmholtz Center Dresden-Rossendorf (HZDR) and alumnus of Kiel University (CAU), now reveals that warm dense matter behaves significantly differently than assumed, which calls into question its previous description.

To study the exotic state of warm dense matter on earth, scientists create it artificially in laboratories. This can be realized by compression through powerful lasers for example at the European XFEL in Schenefeld near Hamburg. “A sample, such as a plastic or aluminum foil, is illuminated with a laser beam, it heats up very strongly and is then compressed by a generated shock wave. The resulting spectra – that means how the sample behaves under these conditions – is recorded on detectors and in a scope of 10-10 m (1 angstrom) we can determine its material properties,” explains Dr. Jan Vorberger from HZDR, adding: “However, important parameters such as temperature or density cannot be measured directly. Therefore, theoretical models are of central importance for the evaluation of the WDM experiments”.

System reacts weaker the more it is perturbed

Tobias Dornheim develops such simulation models for the theoretical description of warm dense matter. From what scientists knew until now, calculations have been based exclusively on the assumption of a “linear reaction”. That means, the more the samples – so called targets – are hit by laser irradiation, thus the more strongly the electrons are excited in these materials, the more strongly they react. In their new publication, however, Dr. Tobias Dornheim of CASUS, Dr. Jan Vorberger of HZDR and Prof. Dr. Michael Bonitz of CAU now show that under strong excitation the reaction is weaker than expected. They conclude that it is crucial to take into account nonlinear effects. The results have far-reaching implications for the interpretation of experiments with warm dense matter. “With this study we have laid the foundation for many new developments in the warm dense matter theory”, Dornheim estimates, “and a lot of research on the nonlinear electronic density response of WDM will be done within the next years.”

Their results are based on extensive computer simulations using the quantum statistical path-integral Monte Carlo method (PIMC). Richard Feynman laid the foundations of the method back in the 1950s. In recent years, Dr. Dornheim has successfully improved the algorithms to make calculations more efficient and faster. Nevertheless, for the mentioned study, supercomputers calculated on more than 10,000 CPU cores for more than 400 days. The calculations were carried out at the high performance clusters Hypnos and Hemera of the HZDR, the Taurus cluster at the Center for Information Services and High Performance Computing (ZIH) of the Technical University of Dresden, computers at the North German Association for High Performance Computing (HLRN) and at the computer center of the CAU.

WDM could play an important role for the energy industry

Research on warm dense matter is not only important for understanding the structure of planets such as Jupiter and Saturn or our solar system and its evolution, but is also applied in materials science, for example in the development of super-hard materials. However, it could play the most important role in the energy industry by contributing to the realization of inertial fusion – an almost inexhaustible and clean energy source with future potential.

See the full article here.

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From École Polytechnique Fédérale de Lausanne: “Machine-learning helps sort out massive materials’ databases”

From École Polytechnique Fédérale de Lausanne

11.09.20
Nik Papageorgiou

EPFL
EPFL and MIT scientists have used machine-learning to organize the chemical diversity found in the ever-growing databases for the popular metal-organic framework materials.

Metal-organic frameworks (MOFs) are a class of materials that contain nano-sized pores. These pores give MOFs record-breaking internal surface areas, which can measure up to 7,800 m^2 in a single gram of material. As a result, MOFs are extremely versatile and find multiple uses: separating petrochemicals and gases, mimicking DNA, producing hydrogen, and removing heavy metals, fluoride anions, and even gold from water are just a few examples.

Because of their popularity, material scientists have been rapidly developing, synthesizing, studying, and cataloguing MOFs. Currently, there are over 90,000 MOFs published, and the number grows every day. Though exciting, the sheer number of MOFs is actually creating a problem: “If we now propose to synthesize a new MOF, how can we know if it is truly a new structure and not some minor variation of a structure that has already been synthesized?” asks Professor Berend Smit at EPFL Valais-Wallis, which houses a major chemistry department.

To address the issue, Smit teamed up with Professor Heather J. Kulik at MIT, and used machine learning to develop a “language” for comparing two materials and quantifying the differences between them. The study is published in Nature Communications.

Armed with their new “language”, the researchers set off to explore the chemical diversity in MOF databases. “Before, the focus was on the number of structures,” says Smit. “But now, we discovered that the major databases have all kinds of bias towards particular structures. There is no point in carrying out expensive screening studies on similar structures. One is better off in carefully selecting a set of very diverse structures, which will give much better results with far fewer structures.”

Another interesting application is “scientific archeology”: The researchers used their machine-learning system to identify the MOF structures that, at the time of the study, were published as very different from the ones that are already known.

“So we now have a very simple tool that can tell an experimental group how different their novel MOF is compared to the 90,000 other structures already reported,” says Smit.

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EPFL campus

EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

From SLAC National Accelerator Lab: “A new X-ray detector snaps 1,000 atomic-level pictures per second of nature’s ultrafast processes”

From SLAC National Accelerator Lab

August 20, 2020
Manuel Gnida

The ePix10k detector is ready to advance science at SLAC’s Linac Coherent Light Source X-ray laser [below] and at facilities around the world.

Scientists around the world use synchrotrons and X-ray lasers to study some of nature’s fastest processes. These machines generate very bright and short X-ray flashes that, like giant strobe lights, “freeze” rapid motions and allow researchers to take sharp snapshots and make movies of atoms buzzing around in a sample.

A new generation of X-ray detectors developed at the Department of Energy’s SLAC National Accelerator Laboratory, called ePix10k, can take up to 1,000 of these snapshots per second – almost 10 times more than previous generations – to make more efficient use of light sources that fire thousands of X-ray flashes per second. Compared to previous ePix and other detectors, this X-ray “camera” can also handle more X-ray intensity, is three times more sensitive, and is available with higher resolution – up to 2 megapixels.

Four units of the ePix10k camera, ready to further X-ray science at SLAC’s Linac Coherent Light Source (LCLS) and facilities worldide. The camera can capture up to 1,000 X-ray images per second, almost 10 times more than previous detector generations. (Christopher Kenney/SLAC National Accelerator Laboratory.)

The ePix10k will become the new workhorse for X-ray science at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, and it’s also benefitting other facilities. Teams at the Advanced Photon Source (APS) at DOE’s Argonne National Laboratory and at European XFEL in Germany are already using the technology, and more groups could follow suit in the near future.

“With the ePix10k, we pushed the state of the art and created a new camera with truly unique features,” says SLAC senior scientist Christopher Kenney, who led the camera construction project. “It’s a great development that is now available to facilities around the world.”

Pushing the limits

SLAC’s ePix X-ray cameras are designed to match the specific needs of scientists who use powerful X-ray light sources to study the atomic details of chemistry, biology and materials. They are fast, perform stably over long periods of time and are sensitive to a broad range of X-ray intensities, meaning they can handle extremely bright X-ray beams as well as single photons.

The cameras consist of two major core parts: a light-sensitive sensor and an application-specific integrated circuit, or ASIC, that processes the signals picked up by the sensor and gives the camera its unique properties.

Previous detectors, such as ePix100 used by LCLS scientists for several years, were tailored to maximize performance at the X-ray laser’s firing rate of 120 pulses per second. SLAC’s detector team further developed the technology so that it can now be used to capture up to 1,000 images per second.

“When we started the project, we already knew that our ASICs could handle higher rates, but it wasn’t clear how far we could push the rest of the technology,” says SLAC electrical engineer Maciej Kwiatkowski.

It turns out the path to a detector that can take images at a 10 times higher rate was relatively straightforward: Without the need to change any of the camera’s hardware, the team reached the new specifications by upgrading and tuning only the device’s firmware, which is similar to a program that is embedded in the camera and defines its functionality.

“The real challenge was to adjust the camera’s parameters to operate at the new speed limit without degrading camera performance,” says SLAC physicist Gabriel Blaj, who was in charge of testing the new device. “But in the end, we were able to use the technology we’ve been developing for several years and run it faster.”

Applications around the world

To get the camera ready for its use at LCLS, the team tested it first with an X-ray tube at SLAC. Last year, they also took a prototype to the BioCARS beamline at APS, an experimental station for studies of processes in biology and chemistry.

One of the techniques used at the beamline is time-resolved serial crystallography, in which researchers shoot laser light at a jet of tiny crystals and use APS X-rays to examine how the crystals’ atomic structure responds to the laser stimulus.

“We apply this method to proteins to learn, for instance, how enzymes catalyze important biological reactions,” says BioCARS operations manager Robert Henning from the University of Chicago. “In principle, we could do these experiments with up to 1,000 X-ray pulses per second at APS, but most detectors can’t handle the full intensity associated with that rate.”

The new ePix X-ray camera, capable of taking up to 1,000 images per second, has been tested at the BioCARS experimental station at Argonne National Laboratory’s Advanced Photon Source. This video, recorded with the camera during the tests, shows a changing pattern of X-rays scattered by crystals. (Robert Henning/University of Chicago, Gabriel Blaj/SLAC National Accelerator Laboratory)

The new detector will let scientists use the X-ray source’s full firing power, saving them a lot of time.

“To obtain a complete data set, we typically need to take thousands of X-ray shots,” Henning says. “Being able to use every single one of APS’s pulses will cut down the time it takes to accomplish that.”

The new ePix detector is also already in use at the European XFEL, a powerful new X-ray laser in Germany that will eventually fire up to 27,000 times per second. SLAC has partnered with Rayonix, a company that develops X-ray detectors for research, to commercialize the technology under a DOE Small Business Innovation Research grant.

Scalable in size

One important feature of the ePix detector is that individual units can be tiled together into a larger detector, which improves the resolution of the X-ray images it takes. Last year’s tests at APS were done with a single unit containing 130,000 pixels. Henning’s team has now ordered a model that will combine 16 of these units into a 2.2-megapixel detector about a foot across.

A new 16-unit version has also been installed at LCLS, which just came back online after a major upgrade of its undulator magnets. The upgrade, together with the new detector, will allow scientists to study the motions of atoms with higher resolution than before.

A 16-module, 2.2-megapixel ePix10k X-ray camera has been installed at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser. (Tim van Driel/SLAC National Accelerator Laboratory)

“The detector will become the new workhorse for our science,” says LCLS instrument scientist Tim van Driel. “It can handle 100 times more X-ray intensity and is much larger than the previous version, ePix100. It’ll also replace other large-area detectors that we’ve been using for the past 10 years.”

Van Driel studies how molecules scatter and absorb X-rays in solution to learn more about chemical processes, such as bond breaking and formation, on an atomic level. But extracting this information is challenging.

“The signals we’re looking for are subtle changes in X-ray intensity – a thousand times smaller than the background intensity,” he says. “So, we need a very flexible detector that can adjust its sensitivity so that it can handle tens of thousands of photons per second of background signals while detecting very few, even single photons associated with tiny chemical changes. The new device is designed to switch automatically between different sensitivities, so it’s just the right detector for the job.”

Future challenges

Delivering the ePix10k technology with a frame rate of 1,000 images per second is a major milestone, but the next challenge already awaits SLAC’s X-ray detector developers.

The next-generation X-ray laser LCLS-II [depicted below], currently under construction at SLAC, will produce up to a million pulses per second, and no X-ray detector in the world today is able to keep up with that speed.

“Our detector team has a plan,” says SLAC senior engineer Angelo Dragone, who is in charge of detector R&D strategic planning at the lab. “A new generation of detectors, ePixHR, will be able to take 5,000 and 25,000 images per second. It’s already in the prototyping phase, and our ultimate goal is to further push that technology to 100,000 images per second.”

In addition, the team is working on a revolutionary new class of cameras, called SparkPix, which will be able to collect images at the same high rate at which LCLS-II will fire X-ray pulses and to process data in real time.

This work was supported by the DOE Office of Science. LCLS and APS are Office of Science user facilities.

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SLAC National Accelerator Lab

SLAC/LCLS

SLAC/LCLS II projected view

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.

SSRL and LCLS are DOE Office of Science user facilities.

From Princeton University – Discovery Magazine: “Princeton scientists discover a topological magnet that exhibits exotic quantum effects”

From Princeton University – Discovery Magazine

July 22, 2020
Hasan group, Princeton University Department of Physics

An international team led by researchers at Princeton University has uncovered a new class of magnet that exhibits novel quantum effects that extend to room temperature.

The researchers discovered a quantized topological phase in a pristine magnet. Their findings provide insights into a 30-year-old theory of how electrons spontaneously quantize and demonstrate a proof-of-principle method to discover new topological magnets. Quantum magnets are promising platforms for dissipationless current, high storage capacity and future green technologies. The study was published in the journal Nature this week.

The arrows represent the electron spins pointing up from a kagome lattice. The chirality is represented by the counterclockwise circle of fire, which represents the propagating electrons/current on the edge of the magnet. The two cones demonstrate that the bulk of the magnet contains Dirac fermions (linear or conical dispersion of bands) with an energy gap (Chern gap), making it topological.

The discovery’s roots lie in the workings of the quantum Hall effect– a form of topological effect which was the subject of the Nobel Prize in Physics in 1985. This was the first time that a branch of theoretical mathematics, called topology, would start to fundamentally change how we describe and classify matter that makes up the world around us. Ever since, topological phases have been intensely studied in science and engineering. Many new classes of quantum materials with topological electronic structures have been found, including topological insulators and Weyl semimetals. However, while some of the most exciting theoretical ideas require magnetism, most materials explored have been nonmagnetic and show no quantization, leaving many tantalizing possibilities unfulfilled.

“The discovery of a magnetic topological material with quantized behavior is a major step forward that could unlock new horizons in harnessing quantum topology for future fundamental physics and next-generation device research” said M. Zahid Hasan, the Eugene Higgins Professor of Physics at Princeton University, who led the research team.

While experimental discoveries were rapidly being made, theoretical physics excelled at developing ideas leading to new measurements. Important theoretical concepts on 2D topological insulators were put forward in 1988 by F. Duncan Haldane, the Thomas D. Jones Professor of Mathematical Physics and the Sherman Fairchild University Professor of Physics at Princeton, who in 2016 was awarded the Nobel Prize in Physics for theoretical discoveries of topological phase transitions and topological phases of matter. Subsequent theoretical developments showed that topological insulator-hosting magnetism in a special atomic arrangement known as a kagome lattice can host some of the most bizarre quantum effects.

Hasan and his team has been on a decade-long search for a topological magnetic quantum state that may also operate at room temperature since their discovery of the first examples of three dimensional topological insulators. Recently, they found a materials solution to Haldane’s conjecture in a kagome lattice magnet that is capable of operating at room temperature, which also exhibits the much desired quantization. “The kagome lattice can be designed to possess relativistic band crossings and strong electron-electron interactions. Both are essential for novel magnetism. Therefore, we realized that kagome magnets are a promising system in which to search for topological magnet phases as they are like the topological insulators that we studied before,” said Hasan.

For so long, direct material and experimental visualization of this phenomenon has remained elusive. The team found that most of the kagome magnets were too difficult to synthesize, the magnetism was not sufficiently well understood, no decisive experimental signatures of the topology or quantization could be observed, or they operate only at very low temperatures.

“A suitable atomic chemistry and magnetic structure design coupled to first-principles theory is the crucial step to make Duncan Haldane’s speculative prediction realistic in a high-temperature setting,” said Hasan. “There are hundreds of kagome magnets, and we need both intuition, experience, materials-specific calculations, and intense experimental efforts to eventually find the right material for in-depth exploration. And that took us on a decade-long journey.”

Through several years of intense research on several families of topological magnets (Nature; Nature Physics; Physical Review Letters; Nature Communications; and Physical Review Letters ), the team gradually realized that a material made of the elements terbium, magnesium and tin (TbMn6Sn6) has the ideal crystal structure with chemically pristine, quantum mechanical properties and spatially segregated kagome lattice layers. Moreover, it uniquely features a strong out-of-plane magnetization. With this ideal kagome magnet successfully synthesized at the large single crystal level by collaborators from Shuang Jia’s group at Peking University, Hasan’s group began systematic state-of-the-art measurements to check whether the crystals are topological and, more important, feature the desired exotic quantum magnetic state.

The Princeton team of researchers used an advanced technique known as scanning tunneling microscopy, which is capable of probing the electronic and spin wavefunctions of a material at the sub-atomic scale with sub-millivolt energy resolution. Under these fine-tuned conditions, the researchers identified the magnetic kagome lattice atoms in the crystal, findings that were further confirmed by state-of-the-art angle-resolved photoemission spectroscopy with momentum resolution.

“The first surprise was that the magnetic kagome lattice in this material is super clean in our scanning tunneling microscopy,” said Songtian Sonia Zhang, a co-author of the study who earned her Ph.D. at Princeton earlier this year. “The experimental visualization of such a defect-free magnetic kagome lattice offers an unprecedented opportunity to explore its intrinsic topological quantum properties.”

The real magical moment was when the researchers turned on a magnetic field. They found that the electronic states of the kagome lattice modulate dramatically, forming quantized energy levels in a way that is consistent with Dirac topology. By gradually raising the magnetic field to 9 Tesla, which is hundreds of thousands of times higher than the earth’s magnetic field, they systematically mapped out the complete quantization of this magnet. “It is extremely rare — there has not been one found yet — to find a topological magnetic system featuring the quantized diagram. It requires a nearly defect-free magnetic material design, fine-tuned theory and cutting-edge spectroscopic measurements” said Nana Shumiya, a graduate student and co-author of the study.

The quantized diagram that the team measured provides precise information revealing that the electronic phase matches a variant of the Haldane model. It confirms that the crystal features a spin-polarized Dirac dispersion with a large Chern gap, as expected by the theory for topological magnets. However, one piece of the puzzle was still missing. “If this is truly a Chern gap, then based on the fundamental topological bulk-boundary principle, we should observe chiral (one-way traffic) states at the edge of the crystal,” Hasan said.

The final piece fell into place when the researchers scanned the boundary or the edge of the magnet. They found a clear signature of an edge state only within the Chern energy gap. Propagating along the side of the crystal without apparent scattering (which reveals its dissipationless character), the state was confirmed to be the chiral topological edge state. Imaging of this state was unprecedented in any previous study of topological magnets.

The researchers further used other tools to check and reconfirm their findings of the Chern gapped Dirac fermions, including electrical transport measurements of anomalous Hall scaling, angle-resolved photoemission spectroscopy of the Dirac dispersion in momentum space, and first-principles calculations of the topological order in the material family. The data provided a complete spectrum of inter-linked evidence all pointing to the realization of a quantum-limit Chern phase in this kagome magnet. “All the pieces fit together into a textbook demonstration of the physics of Chern-gapped magnetic Dirac fermions,” said Tyler A. Cochran, a graduate student and co-first author of the study.

The researchers further used other tools to check and reconfirm their findings of the Chern gapped Dirac fermions, including electrical transport measurements of anomalous Hall scaling, angle-resolved photoemission spectroscopy of the Dirac dispersion in momentum space, and first-principles calculations of the topological order in the material family. The data provided a complete spectrum of inter-linked evidence all pointing to the realization of a quantum-limit Chern phase in this kagome magnet. “All the pieces fit together into a textbook demonstration of the physics of Chern-gapped magnetic Dirac fermions,” said Tyler A. Cochran, a graduate student and co-first author of the study.

Now the theoretical and experimental focus of the group is shifting to the dozens of compounds with similar structures to TbMn6Sn6 that host kagome lattices with a variety of magnetic structures, each with its individual quantum topology. “Our experimental visualization of the quantum limit Chern phase demonstrates a proof-of-principle methodology to discover new topological magnets,” said Jia-Xin Yin, a senior postdoctoral researcher and another co-first author of the study.

“This is like discovering water in an exoplanet – it opens up a new frontier of topological quantum matter research our laboratory at Princeton has been optimized for,” Hasan said.

The study, “Quantum-limit Chern magnetism in TbMn6Sn6,” by Jia-Xin Yin, Wenlong Ma, Tyler A. Cochran, Xitong Xu, Songtian S. Zhang, Hung-Ju Tien, Nana Shumiya, Guangming Cheng, Kun Jiang, Biao Lian, Zhida Song, Guoqing Chang, Ilya Belopolski, Daniel Multer, Maksim Litskevich, Zi-Jia Cheng, Xian P. Yang, Bianca Swidler, Huibin Zhou, Hsin Lin, Titus Neupert, Ziqiang Wang, Nan Yao, Tay-Rong Chang, Shuang Jia and M. Zahid Hasan, was published in the journal Nature on July 22, 2020, volume 583, pages 533–536(2020). DOI: 10.1038/s41586-020-2482-7.

The STM experimental work and the theoretical prediction of topological materials were supported by the Gordon and Betty Moore Foundation under grant GBMF9461/HASAN. The ARPES part of the experiment was supported by the U.S. Department of Energy Basic Energy Sciences under grant DOE/BES DE-FG-02-05ER46200 and DE-FG02-99ER45747. Work at Princeton’s Imaging and Analysis Center is supported by the Princeton Center for Complex Materials, a National Science Foundation (NSF)-MRSEC program, under grant DMR-1420541. Additional support comes from the National Science Foundation Graduate Research Fellowship Program under grant number DGE-1656466. This research used resources of the Advanced Light Source, a DOE Office of Science User Facility under grant DE-AC02-05CH11231.

LBNL ALS

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About Princeton: Overview

Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

From SLAC National Accelerator Lab: Updated to add images- “SLAC’s upgraded X-ray laser facility produces first light”

From SLAC National Accelerator Lab

July 17, 2020

Marking the beginning of the LCLS-II era, the first phase of the major upgrade comes online.

Just over a decade ago in April 2009, the world’s first hard X-ray free-electron laser (XFEL) produced its first light at the US Department of Energy’s SLAC National Accelerator Laboratory. The Linac Coherent Light Source (LCLS) generated X-ray pulses a billion times brighter than anything that had come before. Since then, its performance has enabled fundamental new insights in a number of scientific fields, from creating “molecular movies” of chemistry in action to studying the structure and motion of proteins for new generations of pharmaceuticals and replicating the processes that create “diamond rain” within giant planets in our solar system.

The next major step in this field was set in motion in 2013, launching the LCLS-II upgrade project to increase the X-ray laser’s power by thousands of times, producing a million pulses per second compared to 120 per second today. This upgrade is due to be completed within the next two years.

Today the first phase of the upgrade came into operation, producing an X-ray beam for the first time using one critical element of the newly installed equipment.

“The LCLS-II project represents the combined effort of five national laboratories from across the US, along with many colleagues from the university community and DOE,” said SLAC Director Chi-Chang Kao. “Today’s success reflects the tremendous value of ongoing partnerships and collaboration that enable us to build unique world-leading tools and capabilities.”

XFELs work in a two-step process. First, they accelerate a powerful electron beam to nearly the speed of light. They then pass this beam through an exquisitely tuned series of magnets within a device known as an undulator, which converts the electron energy into intense bursts of X-rays. The bursts are just millionths of a billionth of a second long – so short that they can capture the birth of a chemical bond and produce images with atomic resolution. The LCLS-II project will transform both elements of the facility – by installing an entirely new accelerator that uses cryogenic superconducting technology to achieve the unprecedented repetition rates, along with undulators that can provide exquisite control of the X-ray beam.

Powerful and precise

Over the past 18 months, the original LCLS undulator system (above) was removed and replaced with two totally new systems that offer dramatic new capabilities (below). (Andy Freeberg/Alberto Gamazo/SLAC National Accelerator Laboratory)

This video shows how a sequence of carefully designed springs works to counteract the magnetic forces in powerful magnetic devices known as hard X-ray undulator segments. The spring force must exactly match the manetic force in these segments to keep them aligned within millionths of an inch. These segments contain more than 500 magnets and are about 13 feet long. A chain of 32 of these undulator segments will be used at SLAC National Accelerator Laboratory’s LCLS-II X-ray laser to produce X-rays from a powerful electron beam. The video also shows an undulator segment undergoing magnet measurements at Berkeley Lab. (Credits: Matthaeus Leitner and Marilyn Sargent/Berkeley Lab)

The new undulators were designed and prototyped by DOE’s Argonne National Laboratory and built by Lawrence Berkeley National Laboratory, and have been installed at SLAC over the past year. Today, the first of these systems demonstrated its performance in readiness for the experimental campaigns ahead. Scientists in the SLAC Accelerator Control Room were able to direct the electron beam from the existing LCLS accelerator through the array of magnets in the new “hard X-ray” undulator. Over the course of just a few hours, they produced the first sign of X-rays, and then precisely tuned the configuration to achieve full X-ray laser performance.

“Reaching the first light is a milestone we all have been looking forward to,” said Henrik von der Lippe, Engineering Division director at Berkeley Lab. “This milestone shows how all the hard work and collaboration has resulted in a scientific facility that will enable new science.”

He added, “Berkeley Lab’s contribution of the hard X-ray undulator design and fabrication used our experience from providing undulators to science facilities and our longstanding strength in mechanical design. It is rewarding to see the fruits from years of dedicated Engineering Division teams delivering devices that meet all expectations.”

Images of one of the 21 segments in the soft X-ray undulator (left) and one of the 32 segments in the hard X-ray undulator (right). Each undulator segment is 3.4 meters long. (SLAC National Accelerator Laboratory)

The scientific impact of the new undulators will be significant. One major advance is that the separation between the magnets can be changed on demand, allowing the wavelength of the emitted X-rays to be tuned to match the needs of experiments. Researchers can use this to pinpoint the behavior of selected atoms in a molecule, which among other things will enhance our ability to track the flow and storage of energy for advanced solar power applications.

The undulator demonstrated today is optimized for the hard X-ray regime, and will be able to double the peak X-ray energy LCLS can generate. This will provide much higher precision insights into how materials respond to extreme stress at the atomic level and into the emergence of novel quantum phenomena.

An overlay of LCLS showing the undulator hall, the Front End Enclosure and experimental hall. (SLAC National Accelerator Laboratory)

Next steps

Beyond the undulators lies the Front End Enclosure, or FEE, which contains an array of optics, diagnostics and tuning devices that prepare the X-rays for specific experiments. These include the world’s flattest, smoothest mirrors that are a meter in length but vary in height by only an atom’s width across their surface. Over the next few weeks, these optics will be tested in preparation for more than 80 experiments to be conducted by researchers from around the world over the next six months.

“Today marks the start of the LCLS-II era for X-ray science,” said LCLS Director Mike Dunne. “Our immediate task will be to use this new undulator to investigate the inner workings of the SARS-CoV-2 virus. Then the next couple of years will see an amazing transformation of our facility. Next up will be the soft X-ray undulator, optimized for studying how energy flows between atoms and molecules, and thus the inner workings of novel energy technologies. Beyond this will be the new superconducting accelerator that will increase our X-ray power by many thousands of times. The future is bright, as we like to say in the X-ray laser world.”

See the full article here .

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SLAC National Accelerator Lab

SLAC/LCLS

SLAC/LCLS II projected view

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.

SSRL and LCLS are DOE Office of Science user facilities.

From MIT News: “A wizard of ultrasharp imaging” Frances Ross

From MIT News

July 12, 2020
David L. Chandler

To oversee its new cutting-edge electron microscopy systems, MIT sought out Frances Ross’ industry-honed expertise.

“I’m hoping that MIT becomes a center for electron microscopy,” professor Frances Ross says. “There is nothing that exists with the capabilities that we are aiming for here.” Photo: Jared Charney

A specially designed transmission electron microscope in MIT Materials Research Laboratory’s newly renovated Electron Microscopy (EM) Shared Facility in Building 13. Photo, Denis Paiste, Materials Research Laboratory.

Though Frances Ross and her sister Caroline Ross both ended up on the faculty of MIT’s Department of Materials Science and Engineering, they got there by quite different pathways. While Caroline followed a more traditional academic route and has spent most of her career at MIT, Frances Ross spent most of her professional life working in the industrial sector, as a microscopy specialist at IBM.

IBM Research Ultra High Vacuum-Transmission Electron Microscope Lab In 360.

It wasn’t until 2018 that she arrived at MIT to oversee the new state-of-the-art electron microscope systems being installed in the new MIT.nano facility.

Frances, who bears a strong family resemblance to her sister, says “it’s confused a few people, if they don’t know there are two of us.”

The sisters grew up in London in a strongly science- and materials-oriented family. Her father, who worked first as a scientist and then as a lawyer, is currently working on his third PhD degree, in classics. Her mother, a gemologist, specializes in precisely matching diamonds, and oversees certification testing for the profession.

After earning her doctorate at Cambridge University in materials science, specializing in electron microscopy, Frances Ross went on to do a postdoc at Bell Labs in New Jersey, and then to the National Center for Electron Microscopy at the University of California at Berkeley. From there she continued her work in electron microscopy at IBM in Yorktown Heights, New York, where she spent 20 years working on development and application of electron microscope technology to studying crystal growth.

When MIT built its new cutting-edge nanotechnology fabrication and analysis facility, MIT.nano, it was clear that state-of-the-art microscope technology would need to be a key feature of the new center. That’s when Ross was hired as a professor, along with Professor Jim LeBeau and Research Scientist Rami Dana, who had an academic and industrial research background, to oversee the creation, development, and application of those microscopes for the Department of Materials Science and Engineering (DMSE) and the wider MIT community.

“Currently, our students have to go to other places to do high-performance microscopy, so they might go to Harvard, or one of the national labs,” says Ross, who is the Ellen Swallow Richards Professor in Materials Science and Engineering. “Very many advances in the instrumentation have come together over the last few years, so that if your equipment is a little older, it’s actually a big disadvantage in electron microcopy. This is an area where MIT had not invested for a little while, and therefore, once they made that decision, the jump is going to be very significant. We’re going to have a state-of-the-art imaging capability.”

There will be two major electron microscope systems for materials science, which are gradually taking shape inside the vibration-isolated basement level of MIT.nano, alongside two others already installed that are specialized for biomedical imaging.

One of these will be an advanced version of a standard electron microscope, she says, that will have a unique combination of features. “There is nothing that exists with the capabilities that we are aiming for here.”

The most important of these, she says, is the quality of the vacuum inside the microscope: “In most of our experiments, we want to start with a surface that’s atomically clean.” For example, “we could start with atomically clean silicon, and then add some germanium. How do the germanium atoms add onto the silicon surface? That’s a very important question for microelectronics. But if the sample is in an environment that’s not well-controlled, then the results you get will depend on how dirty the vacuum is. Contamination may affect the process, and you can’t be sure that what you’re seeing is what happens in real life.” Ross is working with the manufacturers to reach exceptional levels of cleanliness in the vacuum of the electron microscope system being developed now.

But ultra-high-quality vacuum is just one of its attributes. “We combine the good vacuum with capabilities to heat the sample, and flow gases, and record images at high speed,” Ross says. “Perhaps most importantly for a lot of our experiments, we use lower-energy electrons to do the imaging, because for many interesting materials like 2D materials, such as graphene, boron nitride, and related structures, the high-energy electrons that are normally used will damage the sample.”

Putting that all together, she says, “is a unique instrument that will give us real insights into surface reactions, crystal growth processes, materials transformations, catalysis, all kinds of reactions involving nanostructure formation and chemistry on the surfaces of 2D materials.”

Other instruments and capabilities are also being added to MIT’s microscopy portfolio. A new scanning transmission electron microscope is already installed in MIT.nano and is providing high-resolution structural and chemical analysis of samples for several projects at MIT. Another new capability is a special sample holder that allows researchers to make movies of unfolding processes in water or other liquids in the microscope. This allows detailed monitoring, at up to 100 frames per second, of a variety of phenomena, such as solution-phase growth, unfolding chemical reactions, or electrochemical processes such as battery charging and discharging. Making movies of processes taking place in water, she says, “is something of a new field for electron microscopy.”

Ross already has set up an ultra-high vacuum electron microscope in DMSE but without the resolution and low-voltage operation of the new instrument. And finally, an ultra-high vacuum scanning tunneling microscope has just started to produce images and will measure current flow through nanoscale materials.

In their free time, Ross and her husband Brian enjoy sailing, mostly off the coast of Maine, with their two children, Kathryn and Eric. As a hobby she collects samples of beach sand. “I have a thousand different kinds of sand from various places, and a lot of them from Massachusetts,” she says. “Everywhere I go, that’s my souvenir.”

But with her intense focus on developing this new world-class microscopy facility, there’s little time for anything else these days. Her aim is to ensure that it’s the best facility possible.

“I’m hoping that MIT becomes a center for electron microscopy,” she says. “You know, with all the interesting materials science and physics that goes on here, it matches up very well with this unique instrumentation, this high-quality combination of imaging and analysis. These unique characterization capabilities really complement the rest of the science that happens here.”

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.

From The Paul Scherrer Institute via phys.org: “Cherned up to the maximum”

From The Paul Scherrer Institute

via

phys.org

Crystals of PdGa can be grown with two distinctstructural chiralities (left and right column). The two enantiomers have mirrored crystalstructures (second row), as seen in electron-reflection patterns (third row). Schröter et al. nowdemonstrate that the handedness are reflected as well in the structure of the Fermi surfaces(bottom row), which determine the electronic behaviour of the material. Both compoundsdisplay the maximal Chern number, but with opposite sign, +4 and -4, respectively. (Adaptedfrom ref. 1.) Credit: Paul Scherrer Institute/Niels Schröter

In topological materials, electrons can display behavior that is fundamentally differentfrom that in ‘conventional’ matter, and the magnitude of many such ‘exotic’ phenomena is directly proportional to an entity known as the Chern number. New experiments establish for the first time that the theoretically predicted maximum Chern number can be reached—and controlled—in a real material.

When the Royal Swedish Academy of Sciences awarded the Nobel Prize in Physics 2016 to David Thouless, Duncan Haldane and Michael Kosterlitz, they lauded the trio for having”opened the door on an unknown world where matter can assume strange states.” Far from being an oddity, the discoveries of topological phase transitions and topological phases of matter, to which the three theoreticians have contributed so crucially, has grown into one of the most active fields of research in condensed matter physics today. Topological materials hold the promise, for instance, to lead to novel types of electronic components and superconductors, and they harbor deep connections across areas of physics and mathematics.

While new phenomena are discovered routinely, there are fundamental aspects yet to be settled. One of those is just how ‘strong’ topological phenomena can be in a real material. Addressing that question, an international team of researchers led by PSI postdoctoral researcher Niels Schröter provide now an important benchmark. Writing in Science, they report experiments in which they observed that in the topological semimetal palladium gallium (PdGa) one of the most common classifiers of topological phenomena, the Chern number, can reach the maximum value that is allowed in any metallic crystal. That this is possible in a real material has never been shown before. Moreover, the team has established ways to control the sign of the Chern number, which might bring new opportunities for exploring, and exploiting, topological phenomena.

Developed to the maximum

In theoretical works it had been predicted that in topological semimetals the Chern number cannot exceed a magnitude of four. As candidate systems displaying phenomena with such maximal Chern numbers, chiral crystals were proposed. These are materials whose lattice structures have a well-defined handedness, in the sense that they cannot transformed into their mirror image by any combination of rotations and translations. Several candidate structures have been studied. A conclusive experimental observation of a Chern number of plus or minus four, however, remained elusive. The previous efforts have been hindered by two factors in particular. First, a prerequisite for realizing a maximal Chern number is the presence of spin-orbit coupling, and at least in some of the materials studied so far, that coupling is relatively low, making it difficult to resolve the splittings of interest. Second,preparing clean and flat surfaces of relevant crystals has been highly challenging, and as a consequence spectroscopic signatures tended to be washed out.

Schröter et al. have overcome both of these limitations by working with PdGa crystals. The material displays strong spin-orbit coupling, and well-established methods exist for producing immaculate surfaces. In addition, at the Advanced Resonant Spectroscopies (ADRESS) beamline of the Swiss Light Source at PSI, they had unique capabilities at their disposal for high-resolution ARPES experiments and thus to resolve the predicted tell-tale spectroscopic patterns.

The Swiss Light Source (SLS) at the Paul Scherrer Institut is a third-generation synchrotron light source. In the design of SLS a high priority was given to the items quality (high brightness), flexibility (wide wavelength spectrum) and stability (very stable temperature conditions) for the primary electron beam and the secondary photon beams. The Swiss National Source is open for international research groups as well as Swiss users, and offers unique research opportunites to academic research teams as well as industrial research groups.

In combination with further measurements at the Diamond Light Source (UK) and with dedicated ab initio calculations, these data revealed hard and fast signatures in the electronic structure of PdGa that left no doubt that the maximal Chern number has been realized.

Diamond Light Source, located at the Harwell Science and Innovation Campus in Oxfordshire U.K.

A hand on the Chern number

The team went one step further, beyond the observation of a maximal Chern number. They showed that the chiral nature of the PdGa crystals offers a possibility to control the sign of that number as well. To demonstrate such control, they grew samples that were either left or right-handed (see the figure). When they looked then at the electronic structures of the two enantiomers, they found that the chirality of the crystals is reflected in the chirality of the electronic wave function. Taken together, this means that in chiral semimetals the handedness, which can be determined during crystal growth, can used to control topological phenomena emerging from the behavior of the electrons in the material.This sort of control opens a trove of new experiments. For example, novel effects can be expected to arise at the interface between different enantiomers, one with Chern number +4 and the other one with -4. And there are real prospects for applications, too. Chiral topological semimetals can host fascinating phenomena such as quantized photocurrents. Intriguingly, PdGa is known for its catalytic properties, inviting the question about the role of topological phenomena in such processes.

Finally, the findings now obtained for PdGa emerge from electronic band properties that are shared by many other chiral compounds—meaning that the corner of the “unknown world where matter can assume strange states” into which Schröter and colleagues have now ventured is likely to have a lot more to offer.

See the full article here.

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From UC San Diego: “$18M Boost to Materials Science Research at UC San Diego”

From UC San Diego

Students and faculty will shape the nano- and bio-materials that will make life better, healthier and safer.

The UC San Diego MRSEC center provides sustained research and educational opportunities for both graduate and undergraduate students, with a particular focus on transfer students. Photos by Erik Jepsen/University Communications.

The National Science Foundation has awarded University of California San Diego researchers a six-year $18 million grant to fund a new Materials Research Science and Engineering Center (MRSEC).

These research centers are transformative for the schools that earn them, putting their materials science research efforts into the global spotlight. In addition to research and facilities funding, MRSEC centers provide sustained research opportunities for both graduate and undergraduate students, and resources to focus on diversifying the pool of students studying materials science.

The UC San Diego labs funded by this new MRSEC will focus on two important, emerging approaches to build new materials aimed at improving human lives.

The first research theme is all about developing new ways to control the properties of materials during their synthesis by controlling how they transition, from the smallest atomic building blocks to materials that are large enough to see with the human eye.

Improved materials for batteries and other technologies that help societies increase renewable energy use will emerge from UC San Diego MRSEC center projects.

The second research theme is focused on creating hybrid materials that incorporate living substances—microbes and plant cells—in order to create materials with new properties.

The new materials developed at UC San Diego will be used to improve the speed and accuracy of medical diagnostic tests, enable more effective therapeutics for disease treatment, quickly and efficiently decontaminate chemical or biological hazards, improve batteries, and reduce the cost of key industrial processes.

“This MRSEC grant is a wonderful affirmation of what we’ve known all along—that UC San Diego is a world-class research and education powerhouse in materials science. This grant is going to enable researchers and students from different disciplines to work together and chart the course for important new avenues for innovation in materials science,” said UC San Diego Chancellor Pradeep K. Khosla.

At the heart of the new MRSEC are student programs designed to diversify materials science and a strong partnership with the educational arm of San Diego’s Fleet Science Center.

The team weaves 19 UC San Diego faculty members and their labs from the Division of Physical Sciences, the Jacobs School of Engineering and the Division of Biological Sciences into a large community of computational and materials science researchers.

A true UC San Diego collaboration.

“Our MRSEC capitalizes on three specific strengths at UC San Diego—our leadership in materials science, our leadership in the life sciences and our position as a national resource in high performance computing,” said Michael Sailor, professor of chemistry and biochemistry at UC San Diego and the leader of the center. “We are weaving the life sciences and high performance computing into materials science. That really makes our center unique.”

The MRSEC is the first big win for the UC San Diego Institute for Materials Discovery and Design (IMDD), which focuses on bridging the gap between physical scientists and engineers on the campus to enable cross-disciplinary research.

“Many of tomorrow’s life-changing discoveries will happen at the intersection of engineering, physical sciences and biological sciences. This is why we pursue such interdisciplinarity here at UC San Diego, and this MRSEC is a tangible result of that effort. It is a tribute to the vision of Mike Sailor, Shirley Meng, Andrea Tao and Jon Pokorski to make the connections necessary to build this world-class team across such varied disciplines,” said Albert P. Pisano, dean of the UC San Diego Jacobs School of Engineering.

This world-class research will directly serve UC San Diego graduate and undergraduate students, including transfer students. According to Sailor, one of the unique challenges for transfer students is that they often do not have the time or the training to participate in the rich research enterprise at UC San Diego.

“Our MRSEC summer schools have a specific focus on bringing transfer students into the materials science research community—the intensive workshops are intended to bring them up to speed so that they can seamlessly enter a research lab. Exposure of undergraduates to cutting-edge research is one of the most important activities of the MRSEC, because fluency in research concepts, tools, and techniques is a key element of a well-trained STEM workforce,” said Steven Boggs, dean of the Division of Physical Sciences at UC San Diego.

Research thrust: predictive assembly

The “predictive assembly” research team is working to bring the computational and predictive tools that the pharmaceutical industry has used successfully to design “small molecule” drugs with particular properties and behaviors into the realm of materials science. The team is led by UC San Diego nanoengineering professors Andrea Tao and Tod Pascal.

Learn more about the predictive assembly project.

The living materials research team is using the tools of biotechnology to build new classes of materials that help make people healthier and safer.

Diversifying the materials science education pipeline.

As part of its core educational mission, the UC San Diego MRSEC team is developing a suite of education programs aimed at growing and diversifying the pipeline for materials scientists in the United States. Summer school workshops, for example, are designed to provide trainees with immersive experience in laboratory procedures, advanced instrumentation and computational methods, explained Stacey Brydges, a professor in the Department of Chemistry & Biochemistry at UC San Diego who oversees the educational elements of the MRSEC.

“We view the summer schools as a transformative mechanism to enhance the training of participants from a broad range of educational levels—from high school to post-graduate,” said Brydges. “We will offer high school and undergraduate students, with particular opportunities for our transfer students, their first introduction to research. The programs will also give incoming graduate students a quick start on their thesis projects.”

Programs will also provide established industrial and international scientists with an update on the “hot topics” by engaging UC San Diego MRSEC researchers.

MRSEC facilities

One of the most important drivers of success in materials research today is the availability of cutting-edge instrumentation. The UC San Diego MRSEC will bring two new, exciting elements to the campus’ research-facilities ecosystem: the Engineered Living Materials Foundry and the MesoMaterials Design Facility.

The predictive assembly research team is weaving computational and predictive tools into the realm of materials science in order to create materials with new, useful properties.

“High-end computation and synthetic biology are both under-represented in the materials science field, and these are areas where we see our MRSEC facilities poised to make a big impact,” said UC San Diego nanoengineering professor Shirley Meng.

She leads the facilities thrust of the MRSEC and is also director of the IMDD. “A major task for our MRSEC is not just to build out the facilities ecosystem but also to train scientists and engineers on how to deploy these tools to enable their research.”

Public outreach

To reach out to the public in new ways, the UC San Diego MRSEC team partnered with San Diego’s Fleet Science Center.

“The goals of many of our community programs and initiatives dovetail nicely with the MRSEC goals,” said Kris Mooney, director of education at the Fleet Science Center.

The MRSEC leverages the Fleet Science Center’s community engagement model, which relies on local community-articulated needs to guide the design and delivery of educational programming.

“When we were setting up the MRSEC, we paid close attention to the diversity of our program at all levels,” said Sailor. “We are particularly focused on diversifying the pipeline for materials science. This is a field that touches the lives of everyone. It’s critical that the people developing the future of materials science reflect society at large.”

See the full article here .

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The University of California, San Diego (also referred to as UC San Diego or UCSD), is a public research university located in the La Jolla area of San Diego, California, in the United States.[12] The university occupies 2,141 acres (866 ha) near the coast of the Pacific Ocean with the main campus resting on approximately 1,152 acres (466 ha).[13] Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is the seventh oldest of the 10 University of California campuses and offers over 200 undergraduate and graduate degree programs, enrolling about 22,700 undergraduate and 6,300 graduate students. UC San Diego is one of America’s Public Ivy universities, which recognizes top public research universities in the United States. UC San Diego was ranked 8th among public universities and 37th among all universities in the United States, and rated the 18th Top World University by U.S. News & World Report ‘s 2015 rankings.

From MIT News: “Exploring interactions of light and matter”

From MIT News

June 30, 2020
David L. Chandler

Juejun Hu pushes the frontiers of optoelectronics for biological imaging, communications, and consumer electronics.

MIT professor Juejun Hu specializes in optical and photonic devices, whose applications include improving high-speed communications, observing the behavior of molecules, and developing innovations in consumer electronics. Image: Denis Paste

Growing up in a small town in Fujian province in southern China, Juejun Hu was exposed to engineering from an early age. His father, trained as a mechanical engineer, spent his career working first in that field, then in electrical engineering, and then civil engineering.

“He gave me early exposure to the field. He brought me books and told me stories of interesting scientists and scientific activities,” Hu recalls. So when it came time to go to college — in China students have to choose their major before enrolling — he picked materials science, figuring that field straddled his interests in science and engineering. He pursued that major at Tsinghua University in Beijing.

He never regretted that decision. “Indeed, it’s the way to go,” he says. “It was a serendipitous choice.” He continued on to a doctorate in materials science at MIT, and then spent four and a half years as an assistant professor at the University of Delaware before joining the MIT faculty. Last year, Hu earned tenure as an associate professor in MIT’s Department of Materials Science and Engineering.

In his work at the Institute, he has focused on optical and photonic devices, whose applications include improving high-speed communications, observing the behavior of molecules, designing better medical imaging systems, and developing innovations in consumer electronics such as display screens and sensors.

“I got fascinated with light,” he says, recalling how he began working in this field. “It has such a direct impact on our lives.”

Hu is now developing devices to transmit information at very high rates, for data centers or high-performance computers. This includes work on devices called optical diodes or optical isolators, which allow light to pass through only in one direction, and systems for coupling light signals into and out of photonic chips.

Lately, Hu has been focusing on applying machine-learning methods to improve the performance of optical systems. For example, he has developed an algorithm that improves the sensitivity of a spectrometer, a device for analyzing the chemical composition of materials based on how they emit or absorb different frequencies of light. The new approach made it possible to shrink a device that ordinarily requires bulky and expensive equipment down to the scale of a computer chip, by improving its ability to overcome random noise and provide a clean signal.

The miniaturized spectrometer makes it possible to analyze the chemical composition of individual molecules with something “small and rugged, to replace devices that are large, delicate, and expensive,” he says.

Much of his work currently involves the use of metamaterials, which don’t occur in nature and are synthesized usually as a series of ultrathin layers, so thin that they interact with wavelengths of light in novel ways. These could lead to components for biomedical imaging, security surveillance, and sensors on consumer electronics, Hu says. Another project he’s been working on involved developing a kind of optical zoom lens based on metamaterials, which uses no moving parts.

Hu is also pursuing ways to make photonic and photovoltaic systems that are flexible and stretchable rather than rigid, and to make them lighter and more compact. This could allow for installations in places that would otherwise not be practical. “I’m always looking for new designs to start a new paradigm in optics, [to produce] something that’s smaller, faster, better, and lower cost,” he says.

Hu says the focus of his research these days is mostly on amorphous materials — whose atoms are randomly arranged as opposed to the orderly lattices of crystal structures — because crystalline materials have been so well-studied and understood. When it comes to amorphous materials, though, “our knowledge is amorphous,” he says. “There are lots of new discoveries in the field.”

Hu’s wife, Di Chen, whom he met when they were both in China, works in the financial industry. They have twin daughters, Selena and Eos, who are 1 year old, and a son Helius, age 3. Whatever free time he has, Hu says, he likes to spend doing things with his kids.

Recalling why he was drawn to MIT, he says, “I like this very strong engineering culture.” He especially likes MIT’s strong system of support for bringing new advances out of the lab and into real-world application. “This is what I find really useful.” When new ideas come out of the lab, “I like to see them find real utility,” he adds.

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.