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  • richardmitnick 7:40 pm on July 13, 2021 Permalink | Reply
    Tags: "Custom-made MIT tool probes materials at the nanoscale", , Atomic force microscopy, , , , , Modern materials research has greatly benefited from advanced experimental tools., , Near-field infrared nanoscope and spectroscope, , Scanning Nearfield Optical Microscope or s-SNOM., Scattering-type scanning nearfield optical microscope   

    From Massachusetts Institute of Technology (US) : “Custom-made MIT tool probes materials at the nanoscale” 

    MIT News

    From Massachusetts Institute of Technology (US)

    July 13, 2021
    Elizabeth A. Thomson

    A scattering-type scanning nearfield optical microscope offers advantages to researchers across many disciplines.

    1
    Assistant Professor Long Ju (center) and colleagues have built a new, customized version of a laboratory tool known as near-field infrared nanoscopy and spectroscopy for MIT users. It and an earlier version, also in Ju’s lab, are the first such tools at the Institute. Here graduate student Matthew Yeung, Professor Ju, and postdoc Zhengguang Lu stand beside the new tool. Credit: Long Ju.

    An MIT physicist has built a new instrument of interest to MIT researchers across a wide range of disciplines because it can quickly and relatively inexpensively determine a variety of important characteristics of a material at the nanoscale. It’s capable of not only determining internal properties of a material, such as how that material’s electrical or optical conductivity changes over exquisitely short distances, but also visualizing individual molecules, like proteins.

    “Modern materials research has greatly benefited from advanced experimental tools,” says Long Ju, an assistant professor in the Department of Physics. Ju is an expert on an emerging instrument that combines nanoscopy — the ability to see things at the nanoscale — with spectroscopy, which probes materials by exploring their interactions with light.

    The tool, known as a near-field infrared nanoscope and spectroscope (it is also known as a scattering-type scanning nearfield optical microscope, or s-SNOM), is available commercially. However, “it’s rather challenging for new users, which limits the applications of the technique,” says Ju.

    So the Ju group built its own version of the tool — the first s-SNOM at MIT — and in May completed a second, more advanced version with additional functions. Now both instruments are available to the MIT community, and the Ju group is on hand to provide assistance to MIT users and to develop new functionalities. Ju encourages MIT colleagues to contact him with potential applications or questions.

    “It’s exciting because it’s a platform that can, in principle, host many different materials systems and extract new information from each,” says Ju, who is also affiliated with MIT’s Materials Research Laboratory. “It’s also a platform for some of the best minds in the world — MIT researchers — to conceive things beyond what can be done on a standard s-SNOM.”

    The new tool is based on atomic force microscopy (AFM), in which an extremely sharp metallic tip with a radius of only 20 nanometers, or billionths of a meter, is scanned across the surface of a material. AFM creates a map of the physical features, or topography, of a surface, of such high resolution that it can identify “mountains” or “valleys” less than a nanometer in height or depth.

    Adding light

    Ju is adding light to the equation. Focusing an infrared laser on the AFM tip turns that tip into an antenna “just like the antenna on a television that’s used to receive signals,” he says. And that, in turn, greatly enhances interactions between the light and the material beneath the tip. The back-scattered light collected from those interactions can be analyzed to reveal much more about the surface than would be possible with a conventional AFM.

    The result: “You can get an image of your sample with three orders of magnitude better spatial resolution than that of conventional infrared measurements,” says Ju. In earlier work reported in Nature, he and colleagues published images of graphene taken with AFM and with the new tool. There are features in common between the two, but the near-field image is riddled with bright lines that are not visible in the AFM image. They are domain walls, or the interfaces between two different sections of a material. Those interfaces are key to understanding a material’s structure and properties.

    Images of similar detail can be captured with transmission electron microscopy (TEM), but TEM has some drawbacks. For example, it must be operated in an ultra-high vacuum, and samples must be extremely thin for suspension on a film or membrane. “The former limits the experimental throughput, while the latter is not compatible with most materials,” says Ju.

    In contrast, the near-field nanoscope “can be operated in air, does not require suspension of the sample, and you can work on most solid substrates,” Ju says.

    Many applications

    Ju notes that the near-field tool can not only provide high-resolution images of heights; the analysis of back-scattered light from the machine’s tip can also give important information about a material’s internal properties. For example, it can tell metals from insulators. It can also distinguish between materials with the same chemical composition but different internal structures (think diamond versus pencil lead).

    In an example he describes as “especially cool,” Ju says that the instrument could even be used to watch a material transition from insulator to superconductor as the temperature is changed. It is also capable of monitoring chemical reactions on the nanoscale.

    Ju also notes that the new tool can be operated in different ways for different purposes. For example, he said, the tip of the tool can either be scanned across a surface while being irradiated with a set wavelength of light, or the tip can be parked over a certain area and probed with light of different wavelengths. Different wavelengths of light interact differently with different materials, giving even more information about a given material’s composition or other characteristics.

    Ju, who came to MIT in 2019, is thoroughly enjoying meeting other MIT researchers who might have applications for his machine. “It’s exciting to work with people from different research areas. You can work together to generate new ideas at the cutting edge.”

    This work is sponsored by MIT’s Materials Research Laboratory.

    See the full article here .


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    MIT Campus

    Massachusetts Institute of Technology (US) is a private land-grant research university in Cambridge, Massachusetts. The institute has an urban campus that extends more than a mile (1.6 km) alongside the Charles River. The institute also encompasses a number of major off-campus facilities such as the MIT Lincoln Laboratory, the Bates Center, and the Haystack Observatory, as well as affiliated laboratories such as the Broad and Whitehead Institutes.

    Founded in 1861 in response to the increasing industrialization of the United States, Massachusetts Institute of Technology (US) adopted a European polytechnic university model and stressed laboratory instruction in applied science and engineering. It has since played a key role in the development of many aspects of modern science, engineering, mathematics, and technology, and is widely known for its innovation and academic strength. It is frequently regarded as one of the most prestigious universities in the world.

    As of December 2020, 97 Nobel laureates, 26 Turing Award winners, and 8 Fields Medalists have been affiliated with MIT as alumni, faculty members, or researchers. In addition, 58 National Medal of Science recipients, 29 National Medals of Technology and Innovation recipients, 50 MacArthur Fellows, 80 Marshall Scholars, 3 Mitchell Scholars, 22 Schwarzman Scholars, 41 astronauts, and 16 Chief Scientists of the U.S. Air Force have been affiliated with Massachusetts Institute of Technology (US) . The university also has a strong entrepreneurial culture and MIT alumni have founded or co-founded many notable companies. Massachusetts Institute of Technology (US) is a member of the Association of American Universities (AAU).

    Foundation and vision

    In 1859, a proposal was submitted to the Massachusetts General Court to use newly filled lands in Back Bay, Boston for a “Conservatory of Art and Science”, but the proposal failed. A charter for the incorporation of the Massachusetts Institute of Technology, proposed by William Barton Rogers, was signed by John Albion Andrew, the governor of Massachusetts, on April 10, 1861.

    Rogers, a professor from the University of Virginia (US), wanted to establish an institution to address rapid scientific and technological advances. He did not wish to found a professional school, but a combination with elements of both professional and liberal education, proposing that:

    “The true and only practicable object of a polytechnic school is, as I conceive, the teaching, not of the minute details and manipulations of the arts, which can be done only in the workshop, but the inculcation of those scientific principles which form the basis and explanation of them, and along with this, a full and methodical review of all their leading processes and operations in connection with physical laws.”

    The Rogers Plan reflected the German research university model, emphasizing an independent faculty engaged in research, as well as instruction oriented around seminars and laboratories.

    Early developments

    Two days after Massachusetts Institute of Technology (US) was chartered, the first battle of the Civil War broke out. After a long delay through the war years, MIT’s first classes were held in the Mercantile Building in Boston in 1865. The new institute was founded as part of the Morrill Land-Grant Colleges Act to fund institutions “to promote the liberal and practical education of the industrial classes” and was a land-grant school. In 1863 under the same act, the Commonwealth of Massachusetts founded the Massachusetts Agricultural College, which developed as the University of Massachusetts Amherst (US)). In 1866, the proceeds from land sales went toward new buildings in the Back Bay.

    Massachusetts Institute of Technology (US) was informally called “Boston Tech”. The institute adopted the European polytechnic university model and emphasized laboratory instruction from an early date. Despite chronic financial problems, the institute saw growth in the last two decades of the 19th century under President Francis Amasa Walker. Programs in electrical, chemical, marine, and sanitary engineering were introduced, new buildings were built, and the size of the student body increased to more than one thousand.

    The curriculum drifted to a vocational emphasis, with less focus on theoretical science. The fledgling school still suffered from chronic financial shortages which diverted the attention of the MIT leadership. During these “Boston Tech” years, Massachusetts Institute of Technology (US) faculty and alumni rebuffed Harvard University (US) president (and former MIT faculty) Charles W. Eliot’s repeated attempts to merge MIT with Harvard College’s Lawrence Scientific School. There would be at least six attempts to absorb MIT into Harvard. In its cramped Back Bay location, MIT could not afford to expand its overcrowded facilities, driving a desperate search for a new campus and funding. Eventually, the MIT Corporation approved a formal agreement to merge with Harvard, over the vehement objections of MIT faculty, students, and alumni. However, a 1917 decision by the Massachusetts Supreme Judicial Court effectively put an end to the merger scheme.

    In 1916, the Massachusetts Institute of Technology (US) administration and the MIT charter crossed the Charles River on the ceremonial barge Bucentaur built for the occasion, to signify MIT’s move to a spacious new campus largely consisting of filled land on a one-mile-long (1.6 km) tract along the Cambridge side of the Charles River. The neoclassical “New Technology” campus was designed by William W. Bosworth and had been funded largely by anonymous donations from a mysterious “Mr. Smith”, starting in 1912. In January 1920, the donor was revealed to be the industrialist George Eastman of Rochester, New York, who had invented methods of film production and processing, and founded Eastman Kodak. Between 1912 and 1920, Eastman donated $20 million ($236.6 million in 2015 dollars) in cash and Kodak stock to MIT.

    Curricular reforms

    In the 1930s, President Karl Taylor Compton and Vice-President (effectively Provost) Vannevar Bush emphasized the importance of pure sciences like physics and chemistry and reduced the vocational practice required in shops and drafting studios. The Compton reforms “renewed confidence in the ability of the Institute to develop leadership in science as well as in engineering”. Unlike Ivy League schools, Massachusetts Institute of Technology (US) catered more to middle-class families, and depended more on tuition than on endowments or grants for its funding. The school was elected to the Association of American Universities (US)in 1934.

    Still, as late as 1949, the Lewis Committee lamented in its report on the state of education at Massachusetts Institute of Technology (US) that “the Institute is widely conceived as basically a vocational school”, a “partly unjustified” perception the committee sought to change. The report comprehensively reviewed the undergraduate curriculum, recommended offering a broader education, and warned against letting engineering and government-sponsored research detract from the sciences and humanities. The School of Humanities, Arts, and Social Sciences and the MIT Sloan School of Management were formed in 1950 to compete with the powerful Schools of Science and Engineering. Previously marginalized faculties in the areas of economics, management, political science, and linguistics emerged into cohesive and assertive departments by attracting respected professors and launching competitive graduate programs. The School of Humanities, Arts, and Social Sciences continued to develop under the successive terms of the more humanistically oriented presidents Howard W. Johnson and Jerome Wiesner between 1966 and 1980.

    Massachusetts Institute of Technology (US)‘s involvement in military science surged during World War II. In 1941, Vannevar Bush was appointed head of the federal Office of Scientific Research and Development and directed funding to only a select group of universities, including MIT. Engineers and scientists from across the country gathered at Massachusetts Institute of Technology (US)’s Radiation Laboratory, established in 1940 to assist the British military in developing microwave radar. The work done there significantly affected both the war and subsequent research in the area. Other defense projects included gyroscope-based and other complex control systems for gunsight, bombsight, and inertial navigation under Charles Stark Draper’s Instrumentation Laboratory; the development of a digital computer for flight simulations under Project Whirlwind; and high-speed and high-altitude photography under Harold Edgerton. By the end of the war, Massachusetts Institute of Technology (US) became the nation’s largest wartime R&D contractor (attracting some criticism of Bush), employing nearly 4000 in the Radiation Laboratory alone and receiving in excess of $100 million ($1.2 billion in 2015 dollars) before 1946. Work on defense projects continued even after then. Post-war government-sponsored research at MIT included SAGE and guidance systems for ballistic missiles and Project Apollo.

    These activities affected Massachusetts Institute of Technology (US) profoundly. A 1949 report noted the lack of “any great slackening in the pace of life at the Institute” to match the return to peacetime, remembering the “academic tranquility of the prewar years”, though acknowledging the significant contributions of military research to the increased emphasis on graduate education and rapid growth of personnel and facilities. The faculty doubled and the graduate student body quintupled during the terms of Karl Taylor Compton, president of Massachusetts Institute of Technology (US) between 1930 and 1948; James Rhyne Killian, president from 1948 to 1957; and Julius Adams Stratton, chancellor from 1952 to 1957, whose institution-building strategies shaped the expanding university. By the 1950s, Massachusetts Institute of Technology (US) no longer simply benefited the industries with which it had worked for three decades, and it had developed closer working relationships with new patrons, philanthropic foundations and the federal government.

    In late 1960s and early 1970s, student and faculty activists protested against the Vietnam War and Massachusetts Institute of Technology (US)’s defense research. In this period Massachusetts Institute of Technology (US)’s various departments were researching helicopters, smart bombs and counterinsurgency techniques for the war in Vietnam as well as guidance systems for nuclear missiles. The Union of Concerned Scientists was founded on March 4, 1969 during a meeting of faculty members and students seeking to shift the emphasis on military research toward environmental and social problems. Massachusetts Institute of Technology (US) ultimately divested itself from the Instrumentation Laboratory and moved all classified research off-campus to the MIT (US) Lincoln Laboratory facility in 1973 in response to the protests. The student body, faculty, and administration remained comparatively unpolarized during what was a tumultuous time for many other universities. Johnson was seen to be highly successful in leading his institution to “greater strength and unity” after these times of turmoil. However six Massachusetts Institute of Technology (US) students were sentenced to prison terms at this time and some former student leaders, such as Michael Albert and George Katsiaficas, are still indignant about MIT’s role in military research and its suppression of these protests. (Richard Leacock’s film, November Actions, records some of these tumultuous events.)

    In the 1980s, there was more controversy at Massachusetts Institute of Technology (US) over its involvement in SDI (space weaponry) and CBW (chemical and biological warfare) research. More recently, Massachusetts Institute of Technology (US)’s research for the military has included work on robots, drones and ‘battle suits’.

    Recent history

    Massachusetts Institute of Technology (US) has kept pace with and helped to advance the digital age. In addition to developing the predecessors to modern computing and networking technologies, students, staff, and faculty members at Project MAC, the Artificial Intelligence Laboratory, and the Tech Model Railroad Club wrote some of the earliest interactive computer video games like Spacewar! and created much of modern hacker slang and culture. Several major computer-related organizations have originated at MIT since the 1980s: Richard Stallman’s GNU Project and the subsequent Free Software Foundation were founded in the mid-1980s at the AI Lab; the MIT Media Lab was founded in 1985 by Nicholas Negroponte and Jerome Wiesner to promote research into novel uses of computer technology; the World Wide Web Consortium standards organization was founded at the Laboratory for Computer Science in 1994 by Tim Berners-Lee; the MIT OpenCourseWare project has made course materials for over 2,000 Massachusetts Institute of Technology (US) classes available online free of charge since 2002; and the One Laptop per Child initiative to expand computer education and connectivity to children worldwide was launched in 2005.

    Massachusetts Institute of Technology (US) was named a sea-grant college in 1976 to support its programs in oceanography and marine sciences and was named a space-grant college in 1989 to support its aeronautics and astronautics programs. Despite diminishing government financial support over the past quarter century, MIT launched several successful development campaigns to significantly expand the campus: new dormitories and athletics buildings on west campus; the Tang Center for Management Education; several buildings in the northeast corner of campus supporting research into biology, brain and cognitive sciences, genomics, biotechnology, and cancer research; and a number of new “backlot” buildings on Vassar Street including the Stata Center. Construction on campus in the 2000s included expansions of the Media Lab, the Sloan School’s eastern campus, and graduate residences in the northwest. In 2006, President Hockfield launched the MIT Energy Research Council to investigate the interdisciplinary challenges posed by increasing global energy consumption.

    In 2001, inspired by the open source and open access movements, Massachusetts Institute of Technology (US) launched OpenCourseWare to make the lecture notes, problem sets, syllabi, exams, and lectures from the great majority of its courses available online for no charge, though without any formal accreditation for coursework completed. While the cost of supporting and hosting the project is high, OCW expanded in 2005 to include other universities as a part of the OpenCourseWare Consortium, which currently includes more than 250 academic institutions with content available in at least six languages. In 2011, Massachusetts Institute of Technology (US) announced it would offer formal certification (but not credits or degrees) to online participants completing coursework in its “MITx” program, for a modest fee. The “edX” online platform supporting MITx was initially developed in partnership with Harvard and its analogous “Harvardx” initiative. The courseware platform is open source, and other universities have already joined and added their own course content. In March 2009 the Massachusetts Institute of Technology (US) faculty adopted an open-access policy to make its scholarship publicly accessible online.

    Massachusetts Institute of Technology (US) has its own police force. Three days after the Boston Marathon bombing of April 2013, MIT Police patrol officer Sean Collier was fatally shot by the suspects Dzhokhar and Tamerlan Tsarnaev, setting off a violent manhunt that shut down the campus and much of the Boston metropolitan area for a day. One week later, Collier’s memorial service was attended by more than 10,000 people, in a ceremony hosted by the Massachusetts Institute of Technology (US) community with thousands of police officers from the New England region and Canada. On November 25, 2013, Massachusetts Institute of Technology (US) announced the creation of the Collier Medal, to be awarded annually to “an individual or group that embodies the character and qualities that Officer Collier exhibited as a member of the Massachusetts Institute of Technology (US) community and in all aspects of his life”. The announcement further stated that “Future recipients of the award will include those whose contributions exceed the boundaries of their profession, those who have contributed to building bridges across the community, and those who consistently and selflessly perform acts of kindness”.

    In September 2017, the school announced the creation of an artificial intelligence research lab called the MIT-IBM Watson AI Lab. IBM will spend $240 million over the next decade, and the lab will be staffed by MIT and IBM scientists. In October 2018 MIT announced that it would open a new Schwarzman College of Computing dedicated to the study of artificial intelligence, named after lead donor and The Blackstone Group CEO Stephen Schwarzman. The focus of the new college is to study not just AI, but interdisciplinary AI education, and how AI can be used in fields as diverse as history and biology. The cost of buildings and new faculty for the new college is expected to be $1 billion upon completion.

    The Caltech/MIT Advanced aLIGO (US) was designed and constructed by a team of scientists from California Institute of Technology (US), Massachusetts Institute of Technology (US), and industrial contractors, and funded by the National Science Foundation (US) .

    MIT/Caltech Advanced aLigo .

    It was designed to open the field of gravitational-wave astronomy through the detection of gravitational waves predicted by general relativity. Gravitational waves were detected for the first time by the LIGO detector in 2015. For contributions to the LIGO detector and the observation of gravitational waves, two Caltech physicists, Kip Thorne and Barry Barish, and Massachusetts Institute of Technology (US) physicist Rainer Weiss won the Nobel Prize in physics in 2017. Weiss, who is also an Massachusetts Institute of Technology (US) graduate, designed the laser interferometric technique, which served as the essential blueprint for the LIGO.

    The mission of Massachusetts Institute of Technology (US) 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 Massachusetts Institute of Technology (US) community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

     
  • richardmitnick 2:01 pm on June 14, 2021 Permalink | Reply
    Tags: "A Keen Eye Behind the Microscope", , Atomic force microscopy, , , Dongsheng Li’s careful crystal formation work unfolds at the nanoscale with powerful equipment., Her group made many discoveries on particle-mediated growth—especially oriented attachment processes—and solid-state phase transformation., In situ transmission electron microscopy, Li devoted a five-year research grant to using high-powered microscopes to examine the formation of branched nanocrystals less than one-thousandth the width of a human hair., , Women in STEM-Dongsheng Li   

    From DOE’s Pacific Northwest National Laboratory (US) : Women in STEM-Dongsheng Li “A Keen Eye Behind the Microscope” 

    From DOE’s Pacific Northwest National Laboratory (US)

    June 14, 2021
    Allan Brettman

    1
    Dongsheng Li’s careful crystal formation work unfolds at the nanoscale with powerful equipment.

    The experiment was not going well, as experiments often do.

    One researcher’s stomach tied in knots.

    Another researcher, materials scientist Dongsheng Li, reacted calmly.

    Li thought of options and alternate approaches to troubleshoot the experiment, unraveling at Pacific Northwest National Laboratory (PNNL). She thought critically, and headed to another building to try different preparation steps.

    Was the experiment back on track lickety-split? No. But it found its course over time. Li made sure of it. She displayed the skill, experience, perseverance, and mental agility that have characterized her work since arriving in 2013 at PNNL as a staff scientist.

    By May 2015, she received an Early Career Research Program Award from the Department of Energy (US) in the highly competitive program. Li devoted the five-year research grant to using high-powered microscopes to examine the formation of branched nanocrystals less than one-thousandth the width of a human hair. Using in situ transmission electron microscopy and atomic force microscopy, her group made many discoveries on particle-mediated growth—especially oriented attachment processes—and solid-state phase transformation.

    Li’s research has been published in Science [only one link, below] regarding two major breakthroughs stemming from the Early Career Award research. In March 2020, she was appointed as a team leader in PNNL’s Physical Sciences Division.

    Microscopy tools to the rescue

    “She has been able to very effectively use microscopy tools to get atomistic information from material systems that provide insights into the mechanisms that lead to a material’s formation,” said Jim De Yoreo, PNNL chief scientist for materials science, who helped recruit Li to the lab. “Her key strength as a researcher is really knowing her methodology and how to utilize it to answer key questions about the synthesis of a material.”

    Growing up in Jilin Province in northeast China, Li’s gravitation toward science came early. There was little time for sports or music, though today she’s a hiker and swimmer, and occasionally plays piano.

    “I was good at math and chemistry and physics when I was in high school,” Li said. “Because of that, I chose to go for this science direction instead of, I don’t know, politics or music or a totally different direction. Science just kind of made sense to me naturally.”

    Li enrolled at Jilin University [国际教育学院] (CN), a state-supported research university whose chemistry program is among the world’s best, according to U.S. News & World Report’s Best Global Universities. Li earned a bachelor’s degree in applied chemistry and a master’s in inorganic chemistry, supported by “Scholarships for Excellent Students” along the way.

    Destined for research. But where?

    She knew early on in her collegiate career that she’d pursue a PhD. And then? “Something in the scientific field,” she said. “Maybe as a professor, a faculty position. And I knew I wanted to come to the United States, to get my PhD here.”

    She enrolled at Pennsylvania State University (US). As she had moved toward chemistry as an undergrad, the same process of following what made sense naturally led her to materials science at Penn State. “Chemistry and materials science are all connected,” she said.

    While working as a postdoc fellow at the University of California-Riverside (US), Li’s postdoc advisor, Professor David Kasailus, introduced her to De Yoreo at a conference. Li said she wanted to work on De Yoreo’s research team at DOE’s Lawrence Berkeley National Laboratory. When De Yoreo went to work at PNNL, Li followed to continue materials research work.

    “She played an important role at Lawrence Berkeley as well as our early research at PNNL, providing expertise in nanoparticle synthesis and electron microscopy for understanding the science of materials synthesis,” De Yoreo said. “Overall, she takes collaboration seriously. She values working together through timely discussions about the research and following through on the details.”

    2
    Electron microscopy reveals nanocrystals self-assembling into pentagonal polygons. Dongsheng Li led a research team that revealed the secret to why nanoparticles sometimes self-assemble into this five-sided shape, which has special properties and is useful in medical research, electronics, and other applications. (Photo: AAAS)

    Li’s materials science research at LBNL and PNNL has been published in Science regarding two major breakthroughs: Understanding the process of oriented attachment in an iron oxyhydroxide system and describing why and how five-fold twin nanoparticles form [Science].

    In the latter breakthrough, Li and her colleagues used a combination of high-resolution transmission electron microscopy combined with molecular dynamics simulation techniques to probe why the structures form as they do. Nanomaterials with this structure have already been shown to have useful properties, such as light responsiveness. They are deployed in medical research for precisely tagging cancerous tumors for imaging and tracking, and in electronics, where they are valued for their mechanical strength.

    “Natural and synthetic nanoparticles composed of five-fold twinned crystal domains have unique properties,” said Li, who led the research team. “But the formation mechanism of these five-fold twinned nanoparticles has been poorly understood. For the first time, we directly observed five-fold twin formation in real time and determined the mechanism by which they form. Understanding that mechanism is the fundamental knowledge materials scientists need to design new five-fold twinned nanoparticles with optimized properties for desired applications.”

    A new home for powerful equipment

    4
    The Energy Sciences Center is scheduled to open in fall 2021 on PNNL’s main campus in Richland, Wash. (Rendering: Pacific Northwest National Laboratory.)

    “At the center, I will continue to study oriented attachments,” Li said. “What factors control oriented attachments? And how can oriented attachments control crystal structures—not only at a nanoscale but also at the atomic scale?”

    Li said the ESC will eventually be the home of a new transmission electron microscope (TEM), a device that uses a particle beam of electrons to visualize specimens and generate a highly magnified image. TEMs can magnify objects up to 2 million times.

    “It really has some nice capabilities,” Li said, “especially its research laboratories and flexible-use open spaces.”

    De Yoreo also saw how the ESC will help Li as well as other researchers working in basic energy sciences and electron microscopy.

    “It’s designed to have quiet space. That’s essential for high-quality electron microscopy work,” De Yoreo said. “And it will have the ancillary equipment a researcher needs, such as focused ion beams for preparing samples. The atomic force microscopy suite will be in there, which is complementary work that Dongsheng does. Right now, the equipment essential to her work is located in three separate buildings on the PNNL campus. Bringing all of those capabilities together into one high-quality space will advance her research.”

    At the core of bricks, mortar, quiet suites, and advanced equipment, though, is the researcher. PNNL materials scientist Elias Nakouzi knows that, having observed Li in action during a perilous point in that experiment that was not going well.

    “When I first joined PNNL as a postdoc, Dongsheng was the first person to show me, by her example, what it means to be a scientist at a national laboratory,” Nakouzi said. “The way she tried different approaches to troubleshoot the experiment caught my attention. We all have experiments that occasionally do not go too well. When that happens to me, I remember how Dongsheng successfully handled the situation.”

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

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

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

     
  • richardmitnick 2:29 pm on February 15, 2021 Permalink | Reply
    Tags: "Kagome graphene promises exciting properties", A graphene compound made of carbon atoms and a few nitrogen atoms that form a regular lattice of hexagons and triangles., , Atomic force microscopy, , Kagome graphene, , , Swiss Nanoscience Institute [Schweizerisches Institut für Nanowissenschaften][CH], The researchers' measurements have delivered promising results that point to unusual electrical or magnetic properties., The so-called Kagome lattice behaves like a semiconductor and could also have unusual electrical properties., This behavior clearly distinguishes the material from conventional graphene., University of Basel [Universität Basel] (CH),   

    From University of Basel [Universität Basel] (CH) and U Bern [Universität Bern] (CH): “Kagome graphene promises exciting properties” 

    u-basel-bloc

    From University of Basel [Universität Basel] (CH)

    and

    From U Bern [Universität Bern] (CH)

    1
    Kagome graphene is characterized by a regular lattice of hexagons and triangles. It behaves as a semiconductor and may also have unusual electrical properties. Credit: R. Pawlak, Department of Physics, University of Basel [Universität Basel] (CH).

    Researchers around the world are searching for new synthetic materials with special properties like superconductivity—that is, the conduction of electric current without resistance. These new substances are an important step in the development of highly energy-efficient electronics. The starting material is often a single-layer honeycomb structure of carbon atoms (graphene).

    Theoretical calculations predict that the compound known as kagome graphene should have completely different properties to graphene. Kagome graphene consists of a regular pattern of hexagons and equilateral triangles that surround one another. The name kagome comes from the old Japanese art of kagome weaving, in which baskets are woven in the same pattern.

    Kagome lattice with new properties

    Researchers from the Department of Physics and the Swiss Nanoscience Institute [Schweizerisches Institut für Nanowissenschaften][CH] at the University of Basel [Universität Basel] (CH), working in collaboration with the University of Bern [Universität Bern](CH), have now produced and studied kagome graphene for the first time, as they report in the journal Angewandte Chemie. The researchers’ measurements have delivered promising results that point to unusual electrical or magnetic properties.

    To produce the kagome graphene, the team applied a precursor to a silver substrate by vapor deposition and then heated it to form an organometallic intermediate on the metal surface. Further heating produced kagome graphene, which is made up exclusively of carbon and nitrogen atoms and features the same regular pattern of hexagons and triangles.


    Kagome Graphene. Physicists of the University of Basel [Universität Basel] (CH) have for the first time produced a graphene compound made of carbon atoms and a few nitrogen atoms that form a regular lattice of hexagons and triangles. This honeycomb-shaped, so-called Kagome lattice behaves like a semiconductor and could also have unusual electrical properties. In the future, it may be used in electronic sensors or quantum computers. Credit: Swiss Nanoscience Institute [Schweizerisches Institut für Nanowissenschaften] [CH].

    Strong interactions between electrons

    “We used scanning tunneling and atomic force microscopes to study the structural and electronic properties of the kagome lattice,” reports Dr. Rémy Pawlak, first author of the study. With microscopes of this kind, researchers can probe the structural and electrical properties of materials using a tiny tip—in this case, the tip was terminated with individual carbon monoxide molecules.

    In doing so, the researchers observed that electrons of a defined energy, which is selected by applying an electrical voltage, are “trapped” between the triangles that appear in the crystal lattice of kagome graphene. This behavior clearly distinguishes the material from conventional graphene, where electrons are distributed across various energy states in the lattice—in other words, they are delocalized.

    “The localization observed in kagome graphene is desirable and precisely what we were looking for,” explains Professor Ernst Meyer, who leads the group in which the projects were carried out. “It causes strong interactions between the electrons—and, in turn, these interactions provide the basis for unusual phenomena, such as conduction without resistance.”

    Further investigations planned

    The analyses also revealed that kagome graphene features semiconducting properties—in other words, its conducting properties can be switched on or off, as with a transistor. In this way, kagome graphene differs significantly from graphene, whose conductivity cannot be switched on and off as easily.

    In subsequent investigations, the team will detach the kagome lattice from its metallic substrate and study its electronic properties further. “The flat band structure identified in the experiments supports the theoretical calculations, which predict that exciting electronic and magnetic phenomena could occur in kagome lattices. In the future, kagome graphene could act as a key building block in sustainable and efficient electronic components,” says Ernst Meyer.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Bern [Universität Bern](CH) is a university in the Swiss capital of Bern and was founded in 1834. It is regulated and financed by the Canton of Bern. It is a comprehensive university offering a broad choice of courses and programs in eight faculties and some 150 institutes. With around 17,512 students, Universität Bern is the third biggest University in Switzerland.

    Universität Bern operates at three levels: university, faculties and institutes. Other organizational units include interfaculty and general university units. The university’s highest governing body is the Senate, which is responsible for issuing statutes, rules and regulations. Directly answerable to the Senate is the University Board of Directors, the governing body for university management and coordination. The Board comprises the Rector, the Vice-Rectors and the Administrative Director. The structures and functions of the University Board of Directors and the other organizational units are regulated by the Universities Act. Universität Bern offers about 39 bachelor and 72 master programs, with enrollments of 7,747 and 4,523, respectively. The university also has 2,776 doctoral students. Around 1,561 bachelor, 1,489 master’s degree students and 570 PhD students graduate each year. For some time now, the university has had more female than male students; at the end of 2016, women accounted for 56% of students.

    u-basel-campus

    Purposes

    The University of Basel [Universität Basel] (CH) fosters the development of critically thinking and tolerant individuals who are capable of taking initiative and taking on responsibility. It is the aim of the University to enable these individuals to deepen their knowledge and field-specific academic training and further education.

    Through research and teaching, the University imparts the insights past down over the ages in addition to producing new knowledge. It is guided by the principle of meaningfulness and purpose rather than feasibility.

    The University is aware of the duties arising from knowledge, fulfilling these duties through critical reflection and the services it provides. It takes its own position concerning problems facing society.

    The University realizes its aims by taking responsibility with respect to future generations, the society that supports them, the international academic community and the culture that is passed down from generation to generation.

     
  • richardmitnick 2:15 pm on January 27, 2021 Permalink | Reply
    Tags: "Studies Provide Answers About Promising 2D Materials", , Atomic force microscopy, , Doping - adding impurities such as boron or phosphorus to silicon for example - is essential to developing semiconductors., , In the first study Cha used molybdenum disulfide (MoS2)., Instead because 2D materials are pretty much all surface researchers can sprinkle small molecules known as organic electron donors (OED) onto the surfaces and activate the 2D materials., , , , , Two-dimensional layered materials hold great promise for a number of applications.,   

    From Yale School of Engineering and Applied Science: “Studies Provide Answers About Promising 2D Materials” 

    Yale University

    From Yale School of Engineering and Applied Science

    01/26/2021

    Two-dimensional, layered materials hold great promise for a number of applications, such as alternative platforms for the next-generation of logic and memory devices and flexible energy storage devices. There’s still much, however, that remains unknown about them.

    1
    This visualisation shows layers of graphene used for membranes. Credit: University of Manchester.

    Two studies from the lab of Judy Cha, the Carol and Douglas Melamed Associate Professor of Mechanical Engineering & Materials Science and a member of Yale West Campus Energy Sciences Institute, answer some crucial questions about these materials. Both studies were funded with grants from the Army Research Office (ARO), an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, and have been published in Advanced Electronic Materials.

    In one paper [Advanced Electronic Materials], Cha and her team of researchers, in collaboration with Yale chemistry professors Nilay Hazari and Hailiang Wang, experimentally measured the precise doping effects of small molecules on 2D materials – a first step toward tailoring molecules for modulating the electrical properties of 2D materials. In the process of doing so, they also achieved a very high doping concentration.

    Doping – adding impurities such as boron or phosphorus to silicon, for example – is essential to developing semiconductors. It allows for the tuning of the carrier densities – the number of electrons and other charge-carriers – to produce a functional device. Conventional doping methods, however, tend to be too energy-intensive and potentially damaging to work well for 2D materials.

    Instead, because 2D materials are pretty much all surface, researchers can sprinkle small molecules known as organic electron donors (OED) onto the surfaces, and activate the 2D materials – that is, create surface functionalization. Thanks to organic chemistry, the method is remarkably effective. It also greatly widens the choice for the material being used. For this study, Cha used molybdenum disulfide (MoS2).

    However, to further optimize these materials, researchers need a greater level of precision. They need to know how many electrons each molecule of the OED donates to the 2D material, and how many molecules are needed altogether.

    “By doing so, we can go forward and design properly, knowing how to tweak the molecules and then increase the carrier densities,” Cha said.

    To make this calibration, Cha and her team used atomic force microscopy at the Imaging Core at Yale’s West Campus. For their material, they achieved a doping efficiency of about one electron per molecule, which allowed them to demonstrate the highest doping level ever achieved in MoS2. This was possible only by the precise measurements that were conducted.

    “Now that we know the doping power, we are no longer in the dark space of not knowing where we are,” she said. “Before, we could dope but couldn’t know how effective that doping is. Now we have some target electron densities that we want to achieve and we feel like we know how to get there.”

    In a second paper [Advanced Electronic Materials], Cha’s team looked at the effects of mechanical strain on the ordering of lithium in lithium-ion batteries.

    Current commercial lithium ion batteries use graphite as the anode. When lithium is inserted into the gaps between graphene layers that make up graphite, the gaps need to expand to make room for the lithium atoms.

    “So we asked ‘What if you stopped this expansion?’” Cha said. “We found that local straining affects the ordering of the lithium ion. The lithium ions effectively get slowed down.”

    When there’s a strain energy, lithium is not able to move as freely as before, and more energy is required to force the lithium into its preferred configuration.

    By calculating the exact effects of the strain energy, Cha’s research team was able to precisely demonstrate how much the lithium atoms slow down.

    The study has broader implications, particularly if the field moves away from lithium batteries in favor of those made from other more readily available materials, such as sodium or magnesium, which can also be used for rechargeable batteries.

    “Sodium and magnesium are much larger, so the gap needs to expand much more compared to lithium, so the effects of strain will be much more dramatic,” she said. The experiments in the study provide a similar understanding of the effects that mechanical strain could have on these other materials.

    ARO researchers said Cha’s studies will be very helpful in advancing their own work.

    “The results obtained in these two studies related to novel two dimensional materials are of great importance to develop future advanced Army applications in sensing and energy storage,” said Dr. Pani Varanasi, branch chief, ARO.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Yale School of Engineering and Applied Science Daniel L Malone Engineering Center.

    The Yale School of Engineering & Applied Science is the engineering school of Yale University. When the first professor of civil engineering was hired in 1852, a Yale School of Engineering was established within the Yale Scientific School, and in 1932 the engineering faculty organized as a separate, constituent school of the university. The school currently offers undergraduate and graduate classes and degrees in electrical engineering, chemical engineering, computer science, applied physics, environmental engineering, biomedical engineering, and mechanical engineering and materials science.

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

     
  • richardmitnick 9:23 am on November 21, 2019 Permalink | Reply
    Tags: , Atomic force microscopy, , , , Oxygen like sulfur and selenium is part of the oxygen or “chalcogen” family of elements., ,   

    From Lawrence Berkeley National Lab: “The Beauty of Imperfections: Linking Atomic Defects to 2D Materials’ Electronic Properties” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    November 20, 2019
    Theresa Duque
    tnduque@lbl.gov
    (510) 495-2418

    Scientists at Berkeley Lab reveal oxygen’s hidden talent for filling in atomic gaps in TMDs; and the surprising role of electron spin in conductivity.

    1
    Scanning tunneling microscopy image of an oxygen substituting sulfur (left), and a sulfur vacancy (right) in tungsten disulfide. In comparison, a strand of human DNA is 2.5 nanometers (nm) in diameter, and a strand of human hair is about 100,000 nm wide. (Credit: Berkeley Lab)

    Like any material, atomically thin, 2D semiconductors known as TMDs or transition metal dichalcogenides are not perfect, but their imperfections can actually be a good thing.

    Understanding how defects are structured at the atomic scale, how they are created, and how they interact with electrons are the first steps to designing new advanced materials. However, no one has been able to link useful properties like optical absorption and emission, conductivity, or catalytic function to specific defects in TMDs.

    Now, two studies led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have revealed surprising details on how some atomic defects emerge in TMDs, and how those defects shape the 2D material’s electronic properties. Their findings could provide a more versatile yet targeted platform for designing 2D materials for quantum information science and smaller, more powerful next-generation light-based electronics (optoelectronics).

    A quantum tip for 2D materials

    In the world of materials science, many researchers assumed that the most abundant defects in TMDs were the result of missing atoms or “vacancies” of sulfur in tungsten disulfide (WS2), or selenium vacancies in molybdenum diselenide (MoSe2).

    But as reported in Nature Communications, the researchers found that the defects previously observed with other methods were actually created by oxygen atoms replacing sulfur or selenium atoms, said D. Frank Ogletree, a staff scientist at Berkeley Lab’s Molecular Foundry and a co-author of the two studies.

    Oxygen, like sulfur and selenium, is part of the oxygen or “chalcogen” family of elements. And since chalcogens share similar properties, there isn’t much change in conductivity when an oxygen atom takes the place of a sulfur or selenium atom in a TMD crystal structure, he said.

    2
    Atomic force microscopy image of sulfur vacancy in tungsten disulfide. (Credit: Berkeley Lab)

    “In other words, it’s like exchanging one kind of apple for another,” explained co-lead author Bruno Schuler, a postdoctoral researcher at Berkeley Lab’s Molecular Foundry. “So when an oxygen atom fills in for a missing sulfur or selenium atom, it effectively restores the TMD’s electronic properties.”

    Co-lead author with Schuler is Sara Barja, who was a postdoctoral researcher in Berkeley Lab’s Materials Sciences Division at the time of the Nature Communications study.

    Key to their finding was the use of the Molecular Foundry’s atomic force microscope (AFM), with a single carbon monoxide (CO) molecule acting as an ultrasharp “tip” or probe, and scanning tunneling microscope (STM). They also benefited from state-of-the-art calculations carried out by scientists from Berkeley Lab’s Center for Computational Study of Excited State Phenomena in Energy Materials (C2SEPEM).

    When used with AFM, the CO-tip images the surface atoms at a very high resolution that’s not possible with conventional techniques, and precisely pinpoints the defect’s atomic site; STM provides the defect’s unique electronic fingerprint.

    The combined insights from both of these methods, combined with detailed calculations performed at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), ultimately helped us understand what these defects are and why they behave the way they do,” said author Alexander Weber-Bargioni, who led the studies. Weber-Bargioni is the facility director for Imaging and Manipulation of Nanostructures at Berkeley Lab’s Molecular Foundry.

    NERSC at LBNL

    NERSC Cray Cori II supercomputer, named after Gerty Cori, the first American woman to win a Nobel Prize in science

    NERSC Hopper Cray XE6 supercomputer, named after Grace Hopper, One of the first programmers of the Harvard Mark I computer

    NERSC Cray XC30 Edison supercomputer

    NERSC GPFS for Life Sciences


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF computer cluster in 2003.

    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    Future:

    Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supeercomputer

    NERSC is a DOE Office of Science User Facility.

    The unexpected power of an orbiting electron’s spin.

    In the researchers’ second study, published in Physical Review Letters, they demonstrated how to deliberately create chalcogen vacancies by heating a sample of WS2 in vacuum up to 600 degrees Celsius (1,112 degrees Fahrenheit), resulting in a thermal energy that causes the atoms to vibrate. “The vibrations kick out one of the sulfur atoms, creating an atomic hole in the material’s crystalline structure,” explained lead author Schuler.

    The scientists also discovered that “spin-orbit interaction” – which relates to the properties of electrons orbiting around an atom’s nucleus and in their own inherent directional spin – plays a significant role in the electronic structure of chalcogen vacancies.

    “In many cases the electron orbital and spin are autonomous and do not care about each other,” he said. “But in some cases, as we discovered in our study, they interact and form hybrid states of electronic structure.”

    Schuler noted that the impact of spin-orbit interaction on the electronic structure of defect sites in TMDs wasn’t clearly understood before this study.

    “It wasn’t even on anyone’s radar. We’re the first to prove it not only by quantitatively determining the magnitude of spin-orbit coupling but also by directly imaging the defect’s electronic orbitals,” he said.

    Now that the researchers have successfully demonstrated how to create chalcogen vacancies in TMDs, Schuler said that they plan to explore the engineering of atomic defects in other types of 2D materials, such as the creation of distinct spin-polarized states, which would be useful for realizing atomic quantum light emitters and other such devices.

    Co-corresponding author Jeff Neaton, a senior faculty scientist in Berkeley Lab’s Materials Sciences Division and professor of physics at UC Berkeley, said that Berkeley Lab offers a unique venue for carrying out multidisciplinary studies.

    “By combining novel experiments at the Molecular Foundry with leading-edge theory, and computing defects’ properties at NERSC with computational methods developed at C2SEPEM, we are steps closer to understanding how common defects can be used to tune optoelectronic properties in 2D materials,” he said.

    Participants in the Nature Communications study involved researchers from Berkeley Lab; UC Berkeley; the University of the Basque Country UPV/EHU-CSIC, Basque Foundation for Science, and Donostia International Physics Center, Spain; Ecole Polytechnique Fédérale de Lausanne, Switzerland; the Korea Institute of Science and Technology; Pusan National University, Korea; and the Weizmann Institute of Science, Israel.

    Participants in the Physical Review Letters study involved researchers from Berkeley Lab; UC Berkeley; Weizmann Institute of Science, Israel; Technical University of Munich; University of the Basque Country UPV/EHU-CSIC, Basque Foundation for Science, and Donostia International Physics Center, Spain.

    Postdoctoral researchers Christoph Kastl and Christopher Chen of the Molecular Foundry grew the tungsten disulfide samples for the Nature Communications and Physical Review Letters studies; and Hyejin Ryu, a doctoral researcher at the Advanced Light Source (ALS), grew samples of molybdenum diselenide for the Nature Communications study.

    LBNL ALS

    The work for both studies was supported by the U.S. Department of Energy’s Office of Science, including the Computational Materials Sciences Center for Computational Study of Excited State Phenomena in Energy Materials (C2SEPEM); research at the Molecular Foundry, a DOE Office of Science user facility that specializes in nanoscale science; and resources at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC). Resources at the Advanced Light Source (ALS) were used for the Nature Communications study.

    The U.S. National Science Foundation provided additional funding for the Nature Communications study, and the DOE Early Career Research Program provided additional funding for the Physical Review Letters study.

    NERSC and the ALS are also DOE Office of Science user facilities.

    See the full article here .

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    Please help promote STEM in your local schools.

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    LBNL campus

    LBNL Molecular Foundry

    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.

    University of California Seal

     
  • richardmitnick 1:49 pm on July 10, 2019 Permalink | Reply
    Tags: , , Atomic force microscopy, Computational materials science, Coupled cluster theory, , Kelvin probe force microscopy, , , ,   

    From Argonne Leadership Computing Facility: “Predicting material properties with quantum Monte Carlo” 

    Argonne Lab
    News from Argonne National Laboratory

    From Argonne Leadership Computing Facility

    July 9, 2019
    Nils Heinonen

    1
    For one of their efforts, the team used diffusion Monte Carlo to compute how doping affects the energetics of nickel oxide. Their simulations revealed the spin density difference between bulks of potassium-doped nickel oxide and pure nickel oxide, showing the effects of substituting a potassium atom (center atom) for a nickel atom on the spin density of the bulk. Credit: Anouar Benali, Olle Heinonen, Joseph A. Insley, and Hyeondeok Shin, Argonne National Laboratory.

    Recent advances in quantum Monte Carlo (QMC) methods have the potential to revolutionize computational materials science, a discipline traditionally driven by density functional theory (DFT). While DFT—an approach that uses quantum-mechanical modeling to examine the electronic structure of complex systems—provides convenience to its practitioners and has unquestionably yielded a great many successes throughout the decades since its formulation, it is not without shortcomings, which have placed a ceiling on the possibilities of materials discovery. QMC is poised to break this ceiling.

    The key challenge is to solve the quantum many-body problem accurately and reliably enough for a given material. QMC solves these problems via stochastic sampling—that is, by using random numbers to sample all possible solutions. The use of stochastic methods allows the full many-body problem to be treated while circumventing large approximations. Compared to traditional methods, they offer extraordinary potential accuracy, strong suitability for high-performance computing, and—with few known sources of systematic error—transparency. For example, QMC satisfies a mathematical principle that allows it to set a bound for a given system’s ground state energy (the lowest-energy, most stable state).

    QMC’s accurate treatment of quantum mechanics is very computationally demanding, necessitating the use of leadership-class computational resources and thus limiting its application. Access to the computing systems at the Argonne Leadership Computing Facility (ALCF) and the Oak Ridge Leadership Computing Facility (OLCF)—U.S. Department of Energy (DOE) Office of Science User Facilities—has enabled a team of researchers led by Paul Kent of Oak Ridge National Laboratory (ORNL) to meet the steep demands posed by QMC. Supported by DOE’s Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program, the team’s goal is to simulate promising materials that elude DFT’s investigative and predictive powers.

    To conduct their work, the researchers employ QMCPACK, an open-source QMC code developed by the team. It is written specifically for high-performance computers and runs on all the DOE machines. It has been run at the ALCF since 2011.

    Functional materials

    The team’s efforts are focused on studies of materials combining transition metal elements with oxygen. Many of these transition metal oxides are functional materials that have striking and useful properties. Small perturbations in the make-up or structure of these materials can cause them to switch from metallic to insulating, and greatly change their magnetic properties and ability to host and transport other atoms. Such attributes make the materials useful for technological applications while posing fundamental scientific questions about how these properties arise.

    The computational challenge has been to simulate the materials with sufficient accuracy: the materials’ properties are sensitive to small changes due to complex quantum mechanical interactions, which make them very difficult to model.

    The computational performance and large memory of the ALCF’s Theta system have been particularly helpful to the team. Theta’s storage capacity has enabled studies of material changes caused by small perturbations such as additional elements or vacancies. Over three years the team developed a new technique to more efficiently store the quantum mechanical wavefunctions used by QMC, greatly increasing the range of materials that could be run on Theta.

    ANL ALCF Theta Cray XC40 supercomputer

    Experimental Validation

    Kent noted that experimental validation is a key component of the INCITE project. “The team is leveraging facilities located at Argonne and Oak Ridge National Laboratories to grow high-quality thin films of transition-metal oxides,” he said, including vanadium oxide (VO2) and variants of nickel oxide (NiO) that have been modified with other compounds.

    For VO2, the team combined atomic force microscopy, Kelvin probe force microscopy, and time-of-flight secondary ion mass spectroscopy on VO2 grown at ORNL’s Center for Nanophase Materials Science (CNMS) to demonstrate how oxygen vacancies suppress the transition from metallic to insulating VO2. A combination of QMC, dynamical mean field theory, and DFT modeling was deployed to identify the mechanism by which this phenomenon occurs: oxygen vacancies leave positively charged holes that are localized around the vacancy site and end up distorting the structure of certain vanadium orbitals.

    For NiO, the challenge was to understand how a small quantity of dopant atoms, in this case potassium, modifies the structure and optical properties. Molecular beam epitaxy at Argonne’s Materials Science Division was used to create high quality films that were then probed via techniques such as x-ray scattering and x-ray absorption spectroscopy at Argonne’s Advanced Photon Source (APS) [below] for direct comparison with computational results. These experimental results were subsequently compared against computational models employing QMC and DFT. The APS and CNMS are DOE Office of Science User Facilities.

    So far the team has been able to compute, understand, and experimentally validate how the band gap of materials containing a single transition metal element varies with composition. Band gaps determine a material’s usefulness as a semiconductor—a substance that can alternately conduct or cease the flow of electricity (which is important for building electronic sensors or devices). The next steps of the study will be to tackle more complex materials, with additional elements and more subtle magnetic properties. While more challenging, these materials could lead to greater discoveries.

    New chemistry applications

    Many of the features that make QMC attractive for materials also make it attractive for chemistry applications. An outside colleague—quantum chemist Kieron Burke of the University of California, Irvine—provided the impetus for a paper published in Journal of Chemical Theory and Computation. Burke approached the team’s collaborators with a problem he had encountered while trying to formulate a new method for DFT. Moving forward with his attempt required benchmarks against which to test his method’s accuracy. As QMC was the only means by which sufficiently precise benchmarks could be obtained, the team produced a series of calculations for him.

    The reputed gold standard for many-body system numerical techniques in quantum chemistry is known as coupled cluster theory. While it is extremely accurate for many molecules, some are so strongly correlated quantum-mechanically that they can be thought of as existing in a superposition of quantum states. The conventional coupled cluster method cannot handle something so complicated. Co-principal investigator Anouar Benali, a computational scientist at the ALCF and Argonne’s Computational Sciences Division, spent some three years collaborating on efforts to expand QMC’s capability so as to include both low-cost and highly efficient support for these states that will in future also be needed for materials problems. Performing analysis on the system for which Burke needed benchmarks required this superposition support; he verified the results of his newly developed DFT approach against the calculations generated with Benali’s QMC expansion. They were in close agreement with each other, but not with the results conventional coupled cluster had generated—which, for one particular compound, contained significant errors.

    “This collaboration and its results have therefore identified a potential new area of research for the team and QMC,” Kent said. “That is, tackling challenging quantum chemical problems.”

    The research was supported by DOE’s Office of Science. ALCF and OLCF computing time and resources were allocated through the INCITE program.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    About ALCF
    The Argonne Leadership Computing Facility’s (ALCF) mission is to accelerate major scientific discoveries and engineering breakthroughs for humanity by designing and providing world-leading computing facilities in partnership with the computational science community.

    We help researchers solve some of the world’s largest and most complex problems with our unique combination of supercomputing resources and expertise.

    ALCF projects cover many scientific disciplines, ranging from chemistry and biology to physics and materials science. Examples include modeling and simulation efforts to:

    Discover new materials for batteries
    Predict the impacts of global climate change
    Unravel the origins of the universe
    Develop renewable energy technologies

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

    Argonne Lab Campus


     
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