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  • richardmitnick 12:33 pm on July 15, 2017 Permalink | Reply
    Tags: , , , Iinspiration comes from advances in semiconductor manufacturing, , Nanotechnology, Provide an alternate path for sight and sound to be delivered directly to the brain, Rice team developing flat microscope for the brain, Rice University, Will focus first on vision   

    From Rice: “Rice team developing flat microscope for the brain” 

    Rice U bloc

    Rice University

    July 12, 2017
    Mike Williams

    Rice University engineers have built a lab prototype of a flat microscope they are developing as part of DARPA’s Neural Engineering System Design project. The microscope will sit on the surface of the brain, where it will detect optical signals from neurons in the cortex. The goal is to provide an alternate path for sight and sound to be delivered directly to the brain. (Credit: Rice University)

    Rice University engineers are building a flat microscope, called FlatScope [TM], and developing software that can decode and trigger neurons on the surface of the brain.

    Their goal as part of a new government initiative is to provide an alternate path for sight and sound to be delivered directly to the brain.

    The project is part of a $65 million effort announced this week by the federal Defense Advanced Research Projects Agency (DARPA) to develop a high-resolution neural interface. Among many long-term goals, the Neural Engineering System Design (NESD) program hopes to compensate for a person’s loss of vision or hearing by delivering digital information directly to parts of the brain that can process it.

    Members of Rice’s Electrical and Computer Engineering Department will focus first on vision. They will receive $4 million over four years to develop an optical hardware and software interface. The optical interface will detect signals from modified neurons that generate light when they are active. The project is a collaboration with the Yale University-affiliated John B. Pierce Laboratory led by neuroscientist Vincent Pieribone.

    Current probes that monitor and deliver signals to neurons — for instance, to treat Parkinson’s disease or epilepsy — are extremely limited, according to the Rice team. “State-of-the-art systems have only 16 electrodes, and that creates a real practical limit on how well we can capture and represent information from the brain,” Rice engineer Jacob Robinson said.

    Robinson and Rice colleagues Richard Baraniuk, Ashok Veeraraghavan and Caleb Kemere are charged with developing a thin interface that can monitor and stimulate hundreds of thousands and perhaps millions of neurons in the cortex, the outermost layer of the brain.

    “The inspiration comes from advances in semiconductor manufacturing,” Robinson said. “We’re able to create extremely dense processors with billions of elements on a chip for the phone in your pocket. So why not apply these advances to neural interfaces?”

    Kemere said some teams participating in the multi-institution project are investigating devices with thousands of electrodes to address individual neurons. “We’re taking an all-optical approach where the microscope might be able to visualize a million neurons,” he said.

    That requires neurons to be visible. Pieribone’s Pierce Lab is gathering expertise in bioluminescence — think fireflies and glowing jellyfish — with the goal of programming neurons with proteins that release a photon when triggered. “The idea of manipulating cells to create light when there’s an electrical impulse is not extremely far-fetched in the sense that we are already using fluorescence to measure electrical activity,” Robinson said.

    The scope under development is a cousin to Rice’s FlatCam, developed by Baraniuk and Veeraraghavan to eliminate the need for bulky lenses in cameras. The new project would make FlatCam even flatter, small enough to sit between the skull and cortex without putting additional pressure on the brain, and with enough capacity to sense and deliver signals from perhaps millions of neurons to a computer.

    Alongside the hardware, Rice is modifying FlatCam algorithms to handle data from the brain interface.

    “The microscope we’re building captures three-dimensional images, so we’ll be able to see not only the surface but also to a certain depth below,” Veeraraghavan said. “At the moment we don’t know the limit, but we hope we can see 500 microns deep in tissue.”

    “That should get us to the dense layers of cortex where we think most of the computations are actually happening, where the neurons connect to each other,” Kemere said.

    A team at Columbia University is tackling another major challenge: The ability to wirelessly power and gather data from the interface.

    In its announcement, DARPA described its goals for the implantable package. “Part of the fundamental research challenge will be developing a deep understanding of how the brain processes hearing, speech and vision simultaneously with individual neuron-level precision and at a scale sufficient to represent detailed imagery and sound,” according to the agency. “The selected teams will apply insights into those biological processes to the development of strategies for interpreting neuronal activity quickly and with minimal power and computational resources.”

    “It’s amazing,” Kemere said. “Our team is working on three crazy challenges, and each one of them is pushing the boundaries. It’s really exciting. This particular DARPA project is fun because they didn’t just pick one science-fiction challenge: They decided to let it be DARPA-hard in multiple dimensions.”

    Baraniuk is the Victor E. Cameron Professor of Electrical and Computer Engineering. Robinson, Veeraraghavan and Kemere are assistant professors of electrical and computer engineering.

    See the full article here .

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    Rice U campus

    In his 1912 inaugural address, Rice University president Edgar Odell Lovett set forth an ambitious vision for a great research university in Houston, Texas; one dedicated to excellence across the range of human endeavor. With this bold beginning in mind, and with Rice’s centennial approaching, it is time to ask again what we aspire to in a dynamic and shrinking world in which education and the production of knowledge will play an even greater role. What shall our vision be for Rice as we prepare for its second century, and how ought we to advance over the next decade?

    This was the fundamental question posed in the Call to Conversation, a document released to the Rice community in summer 2005. The Call to Conversation asked us to reexamine many aspects of our enterprise, from our fundamental mission and aspirations to the manner in which we define and achieve excellence. It identified the pressures of a constantly changing and increasingly competitive landscape; it asked us to assess honestly Rice’s comparative strengths and weaknesses; and it called on us to define strategic priorities for the future, an effort that will be a focus of the next phase of this process.

  • richardmitnick 3:12 pm on July 13, 2017 Permalink | Reply
    Tags: , INFO-Integrated Near-Field Optoelectronic, Nanotechnology, , The probe tip also functions as a light source for measuring how a sample responds to illumination, The system uses gallium nitride (GaN) nanowires as the basis of the nanoprobe   

    From NIST: “Sub-microscopic LEDs Shed New Light on Advanced Materials” 


    July 12, 2017
    Media Contact
    Ben Stein
    (301) 975-2763

    Technical Contact
    Kris A. Bertness
    (303) 497-5069

    One of the persistent challenges in 21st century metrology is the need to measure ever-more-detailed properties of ever-smaller things, from microchip features to subcomponents of biological cells. That’s why, four years ago, a team of NIST scientists patented (link is external) the design for a nanoscale probe system that can simultaneously measure the shape, electrical characteristics, and optical response of sample regions a few tens of nanometers (nm, billionths of a meter) wide. 100 nm is about one-thousandth the width of a human hair.

    Matt Brubaker (left) and Kris Bertness with the chamber in which nanowires are formed. No image credit.

    Now the researchers from NIST’s Physical Measurement Laboratory are closing in on a working prototype. The newest version of the device, which has a probe tip that functions as an ultra-tiny LED “spotlight,” holds great promise for identifying cancer-prone tissue, testing materials for improved solar cells, and providing a new way to put circuits on microchips, among other uses.

    The Integrated Near-Field Optoelectronic (INFO) system has the general configuration of an atomic force microscope (AFM), in which a probe tip on the end of a tiny cantilever beam passes a few nanometers over the surface of a sample, recording exact details of its morphology. But the metal-plated INFO probe also serves as a transmitter that projects microwaves into the sample as well as a receiving antenna that detects the altered microwaves coming back out. The nature of that alteration reveals electrical and chemical properties of the material.

    The system uses gallium nitride (GaN) nanowires as the basis of the nanoprobe. “In addition to being a semiconductor, gallium nitride is mechanically very strong,” says group leader Kris Bertness. “It’s a ceramic, kind of like a high-performance kitchen knife. It’s tough as nails.” As a result, the probe – a few hundred nanometers wide at the point and about 4 micrometers (millionths of a meter) long – doesn’t lose its sharpness, which is critical to performance.

    But GaN has another major advantage: It is the material widely used in light-emitting diodes (LEDs). So, in addition to serving as an AFM and microwave transmitter/receiver, the probe tip also functions as a light source for measuring how a sample responds to illumination.

    This image shows the NIST logo made from glowing nanowire LEDs. While the color of the nanowires in the image looks blue, they are actually emitting in the ultraviolet with a wavelength of approximately 380 nm. The other two images, from a scanning electron microscope, show the overall structure of the nanowires.

    Recently, the team found a way to increase the light output of their probe 100-fold by experimenting with the placement and configuration of “n-type” silicon-doped GaN (which has an excess of free electrons) and “p-type” magnesium-doped GaN, which has a surplus of “holes” – areas where electrons are missing. When an electron and hole combine, they release energy in the form of light, as in LEDs. (See illustration.) Conversely, when light strikes the material in a solar cell, its absorbed energy separates electrons and holes, prompting a current to flow.

    “INFO will allow you to illuminate your sample with near-field resolution (tens of nanometers) and also see if the electrical properties of your sample at that exact same location have changed using the microwave sensing method,” Bertness says. “That’s important, for example, in investigating solar cell materials. With this probe, you can see very locally how that conductivity changes when you illuminate it. Similarly, people are working on photodetectors that are based on polycrystalline materials. They would like to know how the grain boundaries differ in their response to light.”

    Integrated circuit fabricators could use INFO to look for defects and identify the exact location of specific dopant areas in ultra-small features. “The channels are now getting so small, about 15 nm or smaller, that where the dopant atoms actually sit matters,” Bertness says. “Nobody used to have to care about that, but now they might be able to sense those locations because you could optically excite the carriers in and out of the dopant atoms and sense the change with the microwave reflection.

    “Another benefit is that the near-ultraviolet light from the probe tip is very tightly focused, so it can also be used to do much higher resolution lithography than you can do in your standard clean room. In conventional lithography, a beam is directed down at the material surface and directed onto specific exposure areas by using a mask. The INFO probe, however, can use a process called ‘direct write’ that doesn’t require a mask. You could program your probe to move in a specific pattern and coordinate that motion with when the light comes on and off, and you would expose just what you needed.”

    There are numerous potential biological applications. For example, there is some evidence that the mechanical stiffness of collagen – the ubiquitous protein that provides support for all parts of the body – may be related to whether cancer cells are more likely to recur or metastasize. “What medical researchers do now is use AFMs to go in and measure the stiffness of tissue,” Bertness says. “But while they’re doing that, they have no way of knowing when the probe is on collagen or something else. INFO might be able to help. Collagen has very interesting, unique optical properties. So, if scientists could illuminate the sample at the same time they’re doing stiffness measurements, they could determine what kind of tissue the probe is over.”

    Increasing the LED light output from the probe required a prolonged research effort involving the development of several key capabilities. One of the most difficult problems was developing selective-area nanowire growth, which is a process through which nanowire growth can be prescribed at specified locations. Identification and control over the crystal polarity that develops as the GaN wires grow was found to be critical in developing this capability. Another was determining the right geometry and formation conditions for the p-type section of the probe.

    “Initially we tried to fabricate the p-type section as an axial extension of the nanowire probe, however the high-temperature growth conditions required for this type of structure precluded effective p-type doping. In principle, a better p-section could be obtained at lower growth temperatures, however an increased radial growth rate caused nanowires to merge together in our LED test samples,” says project scientist Matt Brubaker. “By synthesizing isolated nanowires via selective area nanowire growth, we could avoid the merging issue and use radial growth to our advantage in synthesizing a core-shell geometry.” After achieving the 100-fold increase in light intensity, “we want to start making these probes and applying them,” Bertness says. “We need to do demonstrations and get some publications out there. That will help us look for potential researchers who could benefit from this technology.”

    See the full article here.

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    NIST Campus, Gaitherberg, MD, USA

    NIST Mission, Vision, Core Competencies, and Core Values

    NIST’s mission

    To promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.
    NIST’s vision

    NIST will be the world’s leader in creating critical measurement solutions and promoting equitable standards. Our efforts stimulate innovation, foster industrial competitiveness, and improve the quality of life.
    NIST’s core competencies

    Measurement science
    Rigorous traceability
    Development and use of standards

    NIST’s core values

    NIST is an organization with strong values, reflected both in our history and our current work. NIST leadership and staff will uphold these values to ensure a high performing environment that is safe and respectful of all.

    Perseverance: We take the long view, planning the future with scientific knowledge and imagination to ensure continued impact and relevance for our stakeholders.
    Integrity: We are ethical, honest, independent, and provide an objective perspective.
    Inclusivity: We work collaboratively to harness the diversity of people and ideas, both inside and outside of NIST, to attain the best solutions to multidisciplinary challenges.
    Excellence: We apply rigor and critical thinking to achieve world-class results and continuous improvement in everything we do.

  • richardmitnick 10:07 am on July 13, 2017 Permalink | Reply
    Tags: , Electron valley states, Nanotechnology, , Quantum dots, ,   

    From UCLA: “Technique for measuring and controlling electron state is a breakthrough in quantum computing” 

    UCLA bloc


    July 06, 2017
    Meghan Steele Horan

    UCLA professor HongWen Jiang (center) and graduate students Blake Freeman and Joshua Schoenfield affixing a quantum dot device to the gold plate of a cooling chamber. Nick Penthorn.

    During their research for a new paper on quantum computing, HongWen Jiang, a UCLA professor of physics, and Joshua Schoenfield, a graduate student in his lab, ran into a recurring problem: They were so excited about the progress they were making that when they logged in from home to their UCLA desktop — which allows only one user at a time — the two scientists repeatedly knocked each other off of the remote connection.

    The reason for their enthusiasm: Jiang and his team created a way to measure and control the energy differences of electron valley states in silicon quantum dots, which are a key component of quantum computing research. The technique could bring quantum computing one step closer to reality.

    “It’s so exciting,” said Jiang, a member of the California NanoSystems Institute. “We didn’t want to wait until the next day to find out the outcome.”

    Quantum computing could enable more complex information to be encoded on much smaller computer chips, and it holds promise for faster, more secure problem-solving and communications than today’s computers allow.

    In standard computers, the fundamental components are switches called bits, which use 0s and 1s to indicate that they are off or on. The building blocks of quantum computers, on the other hand, are quantum bits, or qubits.

    The UCLA researchers’ breakthrough was being able to measure and control a specific state of a silicon quantum dot, known as a valley state, an essential property of qubits. The research was published in Nature Communications.

    “An individual qubit can exist in a complex wave-like mixture of the state 0 and the state 1 at the same time,” said Schoenfield, the paper’s first author. “To solve problems, qubits must interfere with each other like ripples in a pond. So controlling every aspect of their wave-like nature is essential.”

    Silicon quantum dots are small, electrically confined regions of silicon, only tens of nanometers across, that can trap electrons. They’re being studied by Jiang’s lab — and by researchers around the world — for their possible use in quantum computing because they enable scientists to manipulate electrons’ spin and charge.

    Besides electrons’ spin and charge, another of their most important properties is their “valley state,” which specifies where an electron will settle in the non-flat energy landscape of silicon’s crystalline structure. The valley state represents a location in the electron’s momentum, as opposed to an actual physical location.

    Scientists have realized only recently that controlling valley states is critical for encoding and analyzing silicon-based qubits, because even the tiniest imperfections in a silicon crystal can alter valley energies in unpredictable ways.

    “Imagine standing on top of a mountain and looking down to your left and right, noticing that the valleys on either side appear to be the same but knowing that one valley was just 1 centimeter deeper than the other,” said Blake Freeman, a UCLA graduate student and co-author of the study. “In quantum physics, even that small of a difference is extremely important for our ability to control electrons’ spin and charge states.”

    At normal temperatures, electrons bounce around, making it difficult for them to rest in the lowest energy point in the valley. So to measure the tiny energy difference between two valley states, the UCLA researchers placed silicon quantum dots inside a cooling chamber at a temperature near absolute zero, which allowed the electrons to settle down. By shooting fast electrical pulses of voltage through them, the scientists were able to move single electrons in and out of the valleys. The tiny difference in energy between the valleys was determined by observing the speed of the electron’s rapid switching between valley states.

    After manipulating the electrons, the researchers ran a nanowire sensor very close to the electrons. Measuring the wire’s resistance allowed them to gauge the distance between an electron and the wire, which in turn enabled them to determine which valley the electron occupied.

    The technique also enabled the scientists, for the first time, to measure the extremely small energy difference between the two valleys — which had been impossible using any other existing method.

    In the future, the researchers hope to use more sophisticated voltage pulses and device designs to achieve full control over multiple interacting valley-based qubits.

    “The dream is to have an array of hundreds or thousands of qubits all working together to solve a difficult problem,” Schoenfield said. “This work is an important step toward realizing that dream.”

    The research was supported by the U.S. Army Research Office.

    See the full article here .

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    UC LA Campus

    For nearly 100 years, UCLA has been a pioneer, persevering through impossibility, turning the futile into the attainable.

    We doubt the critics, reject the status quo and see opportunity in dissatisfaction. Our campus, faculty and students are driven by optimism. It is not naïve; it is essential. And it has fueled every accomplishment, allowing us to redefine what’s possible, time after time.

    This can-do perspective has brought us 12 Nobel Prizes, 12 Rhodes Scholarships, more NCAA titles than any university and more Olympic medals than most nations. Our faculty and alumni helped create the Internet and pioneered reverse osmosis. And more than 100 companies have been created based on technology developed at UCLA.

  • richardmitnick 7:30 pm on July 11, 2017 Permalink | Reply
    Tags: , , Nanotechnology,   

    From Northwestern: “New laser design offers more inexpensive multi-color output” 

    Northwestern U bloc
    Northwestern University

    July 11, 2017
    Kristin Samuelson

    Photo courtesy of John Krzesinski, 2011, Flickr

    From checkout counters at supermarkets to light shows at concerts, lasers are everywhere, and they’re a much more efficient light source than incandescent bulbs. But they’re not cheap to produce.

    A new Northwestern University study has engineered a more cost-effective laser design that outputs multi-color lasing and offers a step forward in chip-based lasers and miniaturization. The findings could allow encrypted, encoded, redundant and faster information flow in optical fibers, as well as multi-color medical imaging of diseased tissue in real time.

    The study was published July 10 in Nature Nanotechnology.

    “In our work, we demonstrated that multi-modal lasing with control over the different colors can be achieved in a single device,” said senior author Teri W. Odom, a Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern. “Compared to traditional lasers, our work is unprecedented for its stable multi-modal nanoscale lasing and our ability to achieve detailed and fine control over the lasing beams.”

    This work offers new insights into the design and mechanism of multi-modal nanoscale lasing based on structural engineering and manipulating the optical band structures of nanoparticle superlattices. Using this technology, the researchers can control the color and intensity of the light by simply varying its cavity architecture.

    See the full article here .

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    Northwestern South Campus
    South Campus

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is recognized nationally and internationally for its educational programs.

  • richardmitnick 6:03 pm on July 3, 2017 Permalink | Reply
    Tags: Delbrück scattering, , Nanophotonics, Nanotechnology, Polarized gamma rays, Quantum vacuum, The Casimir effect, The future Extreme Light Infrastructure in Măgurele Romania, Vacuum studies, Werner Heisenberg's Uncertainty Principle   

    From Inside Science via Don Lincoln at FNAL: “A Study About Nothing” 

    Inside Science

    June 29, 2017
    Yuen Yiu

    Image credits: Abigail Malate

    Scientists find new ways to measure the infinitesimally small fluctuations that exist in a vacuum.

    A vacuum is a space absolutely devoid of matter, at least according to the Merriam-Webster dictionary. But if you talk to a physicist you may get a different answer. According to quantum physics, even vacuums are not completely empty. Constant fluctuations in energy can spontaneously create mass not just out of thin air, but out of absolutely nothing at all.

    “It’s like a boiling sea of appearing and disappearing particle pairs,” said James Koga, a theoretical physicist from the National Institutes for Quantum and Radiological Science and Technology in Kyoto, Japan. The pairs, made up of one particle and one antiparticle, exist for only moments. Koga is investigating the subtle effects caused by these fluctuations.

    This peculiar nature of vacuum, sometimes referred to as “quantum vacuum,” is not just theoretical speculation. It has real, measurable effects on our physical reality. Although these effects are usually far too small to impact even the most sensitive instruments of today, scientists think the picture will change for the miniaturized technologies of tomorrow.

    “In the macroscopic world, we don’t care about these forces at all. You wouldn’t care about it when you are driving a car for instance. It’s totally negligible,” said Alejandro Manjavacas, a physicist specializing in photonics at the University of New Mexico in Albuquerque. “But in the context of nanotechnology or nanophotonics — at a super small scale, these effects will start playing a role.”

    Although the concept of a fluctuating vacuum was theorized and proven during the first half of the last century, scientists are still grappling with the implications. Two recently published papers explore two separate aspects of the same mystery — what happens when there is nothing at all?

    A glistening ocean

    The energy fluctuation in vacuum can be explained by the uncertainty principle of quantum physics. The principle, first introduced by German physicist Werner Heisenberg, states that at any definite point in space, there must exist temporary changes in energy over time. Sometimes this energy is converted into mass, generating particle-antiparticle pairs.

    Most of the time these newly born pairs recombine and vanish before interacting with anything. Because of this, physicists like to refer to these pairs as “virtual particles,” but this doesn’t mean they aren’t real — they just need something to interact with to make their presence felt.

    For this, Koga and his team envision a way to observe this boiling sea of vacuum the same way we see glistening waves in the ocean — with light. In their latest paper, published in Physical Review Letters, they lay down the theoretical groundwork needed for the experiment. Specifically, they want to study photons that bounce off an atomic nucleus in a distinctive way that wouldn’t happen without the “boiling” vacuum acting as the middleman. This peculiar light phenomenon is known as Delbrück scattering, predicted by German-American physicist Max Delbrück in 1933. The effect was later observed experimentally in 1975 — but just barely.

    “[Scientists] could kind of guess that the Delbrück scattering was there, but it was like if you include this effect in your calculation then it agrees more with the data,” said Koga.

    Koga and his team hope to take Delbrück scattering to another level by characterizing the phenomenon’s effect. It is as if scientists knew about air resistance, but still needed to study it further so that engineers could use the knowledge to build an airplane.

    The task is tricky. To measure Delbrück scattering, one must shine light onto trillions of atomic nuclei, which creates a problem. Photons bounce off nuclei, electrons and even each other in all directions, via all kinds of different interactions. How can one distinguish which photon is scattered from what?

    Koga’s team suggests that we use polarized gamma rays. Just like polarized sunglasses can help you see better by filtering out unwanted solar glares, polarized gamma rays can help scientists sift through the gazillions of photons based on their polarization, in addition to energy and scattered angle. As long as one knows where to look for the specific photons that are the results of Delbrück scattering, one should be able to pick them out from the lineup.

    “The point that we are trying to make in our paper is by using a new polarized source, you can almost see the signal isolated,” said Koga.

    But there is just one problem — such an instrument doesn’t exist. At least not yet.

    Enter the future Extreme Light Infrastructure in Măgurele, Romania. This facility will not only provide the polarized gamma rays Koga proposed, but will make some of the brightest gamma rays in the world. This is important because just like a brighter ambient light can shorten the exposure time for taking a photo, a brighter gamma ray can shorten the run time for Koga’s proposed experiment.

    Credit: ELI-NP Romania

    Kazuo Tanaka, the scientific director of the Nuclear Physics division of the future facility, is pleased with Koga’s team’s proposal.

    “I think their proposal is very crystal clear. They calculated how many days of shooting they need for the experiment, and came up with 76 days,” he said. “I think if they do the experiment we can have a very definitive measurement for Delbrück scattering.”

    While the facility is still under construction, and will not be ready for the experiment at least until 2019, a different group of physicists are studying the same nothingness of vacuum, but with a different set of eyes. Instead of beaming light into the vacuum and looking for a glint, physicist Alejandro Manjavacas and his group at the University of New Mexico want to know if the fluctuations of vacuum can actually exert an invisible force on physical objects — as if they were being moved by Jedis.

    The video shows two plates moving towards each other in a vibrating pool of water, an analogy to the Casimir effect that exist in a fluctuating vacuum. Credit: Denysbondar

    The Casimir effect, named after Dutch physicist Henrik Casimir, describes the force that pushes two objects together due to surrounding waves. The effect exists for two beads on a vibrating string, or two boats in a wavy ocean, as well as two particles in a fluctuating vacuum. Much like Delbrück scattering, the Casimir effect was theorized in 1948 and has already been confirmed, in 1996. So, what is left to be discovered?

    “Most of the work that was done on Casimir effect was for systems that weren’t moving, or if they were moving, they were moving in a uniform motion,” said Manjavacas.

    In a paper published in Physical Review Letters, Manjavacas and his colleagues calculated how the Casimir effect can nudge objects that are already spinning and moving. Through calculations, they discovered that when a tiny sphere spins near a flat surface, it will move as if it is rolling down the surface, despite never making contact with it.

    “If you try to make a nanostructure that involves moving parts that are very close together, it is crucial to know what is going to be the effect from these type of forces. You’ll need to know whether it is going to cause the moving parts to get stuck,” said Manjavacas. “Or we can use these forces to our advantage, such as using them to move objects or to force them to do the things that we want.”

    In their study, the researchers evaluated the effect for spheres with diameters ranging from 50 to 500 nanometers, much less than one hundredth the width of a human hair. As expected, the relationship between the spinning and the lateral movement isn’t straightforward — it depends on the speed that the sphere is spinning, as well as the size of the sphere and the distance between the sphere and the surface. These minute effects may soon be relevant on the frontier of technology, for example when engineers design medical nanobots.

    Virtual Particles and Black Holes
    The sidebar image shows a simulated animation of a black hole moving across a galaxy in the background. Credit: Wikicommons/CC BY-SA 3.0
    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?
    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it

    Beyond its impact on nanotechnologies and particle accelerators here on earth, the fluctuating vacuum extends its effects into space. In 1968, British astrophysicist Stephen Hawking predicted that when a particle-antiparticle pair is created on the edge of a black hole’s event horizon, the pair can be pried apart by gravity — one particle falling into the black hole and the other escaping. The escape of one of the particles then contributes to an infinitesimally small, and so far purely theoretical, radiation known as Hawking radiation.
    Hawking radiation, if proven, will play a crucial role in determining the lifetime of black holes. However, even if the radiation is real, it will still be far too faint for us to detect it. There have been a few analogous models that can successfully reproduce the phenomenon in a laboratory setting, but they use light waves or sound waves instead of gravitational waves of black holes. There is hope that the Large Hadron Collider near Geneva, Switzerland, with a higher energy output, can create a super tiny black hole that lasts but a split second, and offer a more definitive answer on Hawking radiation. But for now, no direct observation for Hawking radiation has been possible, leading to some saying that the “jury is still out.”
    “This is a pity, because if they had, I would have got a Nobel prize,” said Hawking during a 2008 lecture.

    A real virtuality

    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?

    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum.”

    Because unlike the ether theory, the quantum model of vacuum, with all its fluctuations and peculiar features, has since been thoroughly tested and proven.

    “We see pair creation all the time actually, like in particle accelerators,” said Koga. In fact, it happens so often that for certain experiments scientists actually have to consider the phenomenon as “noise” that could obscure the signal they are looking for, according to Koga.

    “We now have experimental evidence of all kinds of particles coming in and out [of the vacuum],” said Toshiki Tajima, a physicist from the University of California, Irvine. “Muons and anti-muons, protons and anti-protons, and even quarks and anti-quarks.”

    In 1665, Robert Hooke and Antoni van Leeuwenhoek discovered microbes when they pointed their microscopes at “nothing.” In 1964, Arno Penzias and Robert Woodrow Wilson discovered the cosmic microwave background when they pointed their telescopes at “nothing.” Vacuum is perhaps the ultimate “nothing,” so if history is any indication, “nothing” is an interesting place, especially if you want to look for something.

    See the full article here .

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    Inside Science is brought to you in part through the generous support of The American Physical Society and The Acoustical Society of America and a coalition of underwriters.

  • richardmitnick 12:22 pm on June 27, 2017 Permalink | Reply
    Tags: 1 billion suns: World’s brightest laser sparks new behavior in light, Diocles Laser, Extreme Light Laboratory, Focusing laser light to a brightness 1 billion times greater than the surface of the sun, , Nanotechnology, , U Nebraska,   

    From U Nebraska – Lincoln: “1 billion suns: World’s brightest laser sparks new behavior in light” 

    University of Nebraska -Lincoln

    Scott Schrage

    A rendering of how changes in an electron’s motion (bottom) alter the scattering of light (top), as measured in a new experiment that scattered more than 500 photons of light from a single electron. Previous experiments had managed to scatter no more than a few photons at a time. Donald Umstadter and Wenchao Yan

    Brighter than a billion suns: A scientist at work in the Extreme Light Laboratory. Diocles Laser.
    University of Nebraska-Lincoln. COSMOS.

    Physicists from the University of Nebraska-Lincoln are seeing an everyday phenomenon in a new light.

    By focusing laser light to a brightness 1 billion times greater than the surface of the sun — the brightest light ever produced on Earth — the physicists have observed changes in a vision-enabling interaction between light and matter.

    Those changes yielded unique X-ray pulses with the potential to generate extremely high-resolution imagery useful for medical, engineering, scientific and security purposes. The team’s findings, detailed June 26 in the journal Nature Photonics, should also help inform future experiments involving high-intensity lasers.

    Donald Umstadter and colleagues at the university’s Extreme Light Laboratory fired their Diocles Laser at helium-suspended electrons to measure how the laser’s photons — considered both particles and waves of light — scattered from a single electron after striking it.

    Under typical conditions, as when light from a bulb or the sun strikes a surface, that scattering phenomenon makes vision possible. But an electron — the negatively charged particle present in matter-forming atoms — normally scatters just one photon of light at a time. And the average electron rarely enjoys even that privilege, Umstadter said, getting struck only once every four months or so.

    Though previous laser-based experiments had scattered a few photons from the same electron, Umstadter’s team managed to scatter nearly 1,000 photons at a time. At the ultra-high intensities produced by the laser, both the photons and electron behaved much differently than usual.

    “When we have this unimaginably bright light, it turns out that the scattering — this fundamental thing that makes everything visible — fundamentally changes in nature,” said Umstadter, the Leland and Dorothy Olson Professor of Physics and Astronomy.

    A photon from standard light will typically scatter at the same angle and energy it featured before striking the electron, regardless of how bright its light might be. Yet Umstadter’s team found that, above a certain threshold, the laser’s brightness altered the angle, shape and wavelength of that scattered light.

    “So it’s as if things appear differently as you turn up the brightness of the light, which is not something you normally would experience,” Umstadter said. “(An object) normally becomes brighter, but otherwise, it looks just like it did with a lower light level. But here, the light is changing (the object’s) appearance. The light’s coming off at different angles, with different colors, depending on how bright it is.”

    That phenomenon stemmed partly from a change in the electron, which abandoned its usual up-and-down motion in favor of a figure-8 flight pattern. As it would under normal conditions, the electron also ejected its own photon, which was jarred loose by the energy of the incoming photons. But the researchers found that the ejected photon absorbed the collective energy of all the scattered photons, granting it the energy and wavelength of an X-ray.

    The unique properties of that X-ray might be applied in multiple ways, Umstadter said. Its extreme but narrow range of energy, combined with its extraordinarily short duration, could help generate three-dimensional images on the nanoscopic scale while reducing the dose necessary to produce them.

    Using a laser focused to the brightest intensity yet recorded, physicists at the Extreme Light Laboratory produced unique X-ray pulses with greater energy than their conventional counterparts. The team demonstrated these X-rays by imaging the circuitry of a USB drive. Extreme Light Laboratory | University of Nebraska-Lincoln.

    Those qualities might qualify it to hunt for tumors or microfractures that elude conventional X-rays, map the molecular landscapes of nanoscopic materials now finding their way into semiconductor technology, or detect increasingly sophisticated threats at security checkpoints. Atomic and molecular physicists could also employ the X-ray as a form of ultrafast camera to capture snapshots of electron motion or chemical reactions.

    As physicists themselves, Umstadter and his colleagues also expressed excitement for the scientific implications of their experiment. By establishing a relationship between the laser’s brightness and the properties of its scattered light, the team confirmed a recently proposed method for measuring a laser’s peak intensity. The study also supported several longstanding hypotheses that technological limitations had kept physicists from directly testing.

    “There were many theories, for many years, that had never been tested in the lab, because we never had a bright-enough light source to actually do the experiment,” Umstadter said. “There were various predictions for what would happen, and we have confirmed some of those predictions.

    “It’s all part of what we call electrodynamics. There are textbooks on classical electrodynamics that all physicists learn. So this, in a sense, was really a textbook experiment.”

    Umstadter authored the study with Sudeep Banerjee and Shouyuan Chen, research associate professors of physics and astronomy; Grigory Golovin and Cheng Liu, senior research associates in physics and astronomy; Wenchao Yan, Ping Zhang, Baozhen Zhao and Jun Zhang, postdoctoral researchers in physics and astronomy; Colton Fruhling and Daniel Haden, doctoral students in physics and astronomy; along with Min Chen and Ji Luo of Shanghai Jiao Tong University.

    The team received support from the Air Force Office for Scientific Research, the National Science Foundation, the U.S. Department of Energy’s Office of Science, the Department of Homeland Security’s Domestic Nuclear Detection Office, and the National Science Foundation of China.

    See the full article here .

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    The University of Nebraska–Lincoln, often referred to as Nebraska, UNL or NU, is a public research university in the city of Lincoln, in the state of Nebraska in the Midwestern United States. It is the state’s oldest university, and the largest in the University of Nebraska system.

    The state legislature chartered the university in 1869 as a land-grant university under the 1862 Morrill Act, two years after Nebraska’s statehood into the United States. Around the turn of the 20th century, the university began to expand significantly, hiring professors from eastern schools to teach in the newly organized professional colleges while also producing groundbreaking research in agricultural sciences. The “Nebraska method” of ecological study developed here during this time pioneered grassland ecology and laid the foundation for research in theoretical ecology for the rest of the 20th century. The university is organized into eight colleges on two campuses in Lincoln with over 100 classroom buildings and research facilities.

    Its athletic program, called the Cornhuskers, is a member of the Big Ten Conference. The Nebraska football team has won 46 conference championships, and since 1970, five national championships. The women’s volleyball team has won four national championships along with eight other appearances in the Final Four. The Husker football team plays its home games at Memorial Stadium, selling out every game since 1962. The stadium’s capacity is about 92,000 people, larger than the population of Nebraska’s third-largest city.

  • richardmitnick 7:36 pm on June 26, 2017 Permalink | Reply
    Tags: , Electromagnetic radiation [light], Hyperbolic metamaterials (HMMs), Molecular beam epitaxy, Nanoresonators, Nanotechnology, , , ,   

    From Notre Dame: “Notre Dame Researchers Open Path to New Generation of Optical Devices” 

    Notre Dame bloc

    Notre Dame University


    College of Engineering

    June 22, 2017
    Nina Welding

    Sub-diffraction Confinement in All-semiconductor Hyperbolic Metamaterial Resonators was co-authored by graduate students Kaijun Feng and Galen Harden and Deborah L. Sivco, engineer-in-residence at MIRTHE+ Photonics Sensing Center, Princeton Univ.

    Cameras, telescopes and microscopes are everyday examples of optical devices that measure and manipulate electromagnetic radiation [light]. Being able to control the light in such devices provides the user with more information through a much better “picture” of what is occurring through the lens. The more information one can glean, the better the next generation of devices can become. Similarly, controlling light on small scales could lead to improved optical sources for applications that span health, homeland security and industry. This is what a team of researchers, led by Anthony Hoffman, assistant professor of electrical engineering and researcher in the University’s Center for Nano Science and Technology (NDnano), has been pursuing. Their findings were recently published in the June 19 issue of ACS Photonics.

    In fact, the team has fabricated and characterized sub-diffraction mid-infrared resonators using all-semiconductor hyperbolic metamaterials (HMMs) that confine light to extremely small volumes — thousands of times smaller than common materials.

    The scanning electron microscope image here shows an array of 0.47 μm wide resonators with a 2.5 μm pitch. No image credit.

    HMMs combine the properties of metals, which are excellent conductors, and dielectrics, which are insulators, to realize artificial optical materials with properties that are very difficult, even impossible, to find naturally. These unusual properties may elucidate the quantum mechanical interactions between light and matter at the nanoscale while giving researchers a powerful tool to control and engineer these light-matter interactions for new optical devices and materials.

    Hoffman’s team engineered these desired properties in the HMMs by growing them via molecular beam epitaxy using III-V semiconductor materials routinely used for high-performance optoelectronic devices, such as lasers and detectors. Layers of Si-doped InGaAs and intrinsic AlInAs were placed on top of one another, with a single layer being 50 nm thick. The total thickness of the HMM was 1μm, about 100 times smaller than the width of a human hair.

    The nanoresonators were produced by Kaijun Feng, graduate student in the Department of Electrical Engineering, using state-of-the-art fabrication equipment in Notre Dame’s Nanofabrication Facility. The devices were then characterized in Hoffman’s laboratory using a variety of spectroscopic techniques.

    “What is particularly exciting about this work,” says Hoffman, “is that we have found a way to squeeze light into small volumes using a mature semiconductor technology. In addition to being able to employ these nanoresonators to generate mid-infrared light, we believe that these new sources could have significant application in the mid-infrared portion of the spectrum, which is used for optical sensing across areas such as medicine, environmental monitoring, industrial process control and defense. We are also excited about the possibility of utilizing these nanoresonators to study interactions between light and matter that previously have not been possible.”

    See the full article here .

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    Notre Dame Campus

    The University of Notre Dame du Lac (or simply Notre Dame /ˌnoʊtərˈdeɪm/ NOH-tər-DAYM) is a Catholic research university located near South Bend, Indiana, in the United States. In French, Notre Dame du Lac means “Our Lady of the Lake” and refers to the university’s patron saint, the Virgin Mary.

    The school was founded by Father Edward Sorin, CSC, who was also its first president. Today, many Holy Cross priests continue to work for the university, including as its president. It was established as an all-male institution on November 26, 1842, on land donated by the Bishop of Vincennes. The university first enrolled women undergraduates in 1972. As of 2013 about 48 percent of the student body was female.[6] Notre Dame’s Catholic character is reflected in its explicit commitment to the Catholic faith, numerous ministries funded by the school, and the architecture around campus. The university is consistently ranked one of the top universities in the United States and as a major global university.

    The university today is organized into five colleges and one professional school, and its graduate program has 15 master’s and 26 doctoral degree programs.[7][8] Over 80% of the university’s 8,000 undergraduates live on campus in one of 29 single-sex residence halls, each of which fields teams for more than a dozen intramural sports, and the university counts approximately 120,000 alumni.[9]

    The university is globally recognized for its Notre Dame School of Architecture, a faculty that teaches (pre-modernist) traditional and classical architecture and urban planning (e.g. following the principles of New Urbanism and New Classical Architecture).[10] It also awards the renowned annual Driehaus Architecture Prize.

  • richardmitnick 5:11 pm on June 26, 2017 Permalink | Reply
    Tags: , , Electron beam lithography, Halide perovskites, , Nanotechnology, ,   

    From LBNL: “New Class of ‘Soft’ Semiconductors Could Transform HD Displays” 

    Berkeley Logo

    Berkeley Lab

    June 26, 2017
    Sarah Yang
    (510) 486-4575

    A new type of semiconductor may be coming to a high-definition display near you. Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) have shown that a class of semiconductor called halide perovskites is capable of emitting multiple, bright colors from a single nanowire at resolutions as small as 500 nanometers.

    Single nanowires shown emitting different colors. The top panel shows a cesium lead bromide (CsPbBr3)-cesium lead chloride (CsPbCl3) heterojunction simultaneously emitting green and blue lights, respectively, under UV excitation. The bottom panel shows a cesium lead iodide (CsPbI3)-cesium lead bromide-cesium lead chloride configuration emitting red, green, and blue lights, respectively. (Credit: Letian Dou/Berkeley Lab and Connor G. Bischak/UC Berkeley)

    The findings, published online this week in the early edition of the Proceedings of the National Academy of Sciences, represent a clear challenge to quantum dot displays that rely upon traditional semiconductor nanocrystals to emit light. It could also influence the development of new applications in optoelectronics, photovoltaics, nanoscopic lasers, and ultrasensitive photodetectors, among others.

    The researchers used electron beam lithography to fabricate halide perovskite nanowire heterojunctions, the junction of two different semiconductors. In device applications, heterojunctions determine energy level and bandgap characteristics, and are therefore considered a key building block of modern electronics and photovoltaics.

    The researchers pointed out that the lattice in halide perovskites is held together by ionic instead of covalent bonds. In ionic bonds, atoms of opposite charges are attracted and transfer electrons to each other. Covalent bonds, in contrast, occur when atoms share their electrons with each other.

    “With inorganic halide perovskites, we can easily swap the anions in the ionic bonds while maintaining the single crystalline nature of the materials,” said study principal investigator Peidong Yang, senior faculty scientist at Berkeley Lab’s Materials Sciences Division. “This allows us to easily reconfigure the structure and composition of the material. That’s why halide perovskites are considered soft lattice semiconductors. Covalent bonds, in contrast, are relatively robust and require more energy to change. Our study basically showed that we can pretty much change the composition of any segment of this soft semiconductor.”

    A 2-D plate showing alternating cesium lead chloride (blue) and cesium lead bromide (green) segments. (Credit: Letian Dou/Berkeley Lab and Connor G. Bischak/UC Berkeley)

    In this case, the researchers tested cesium lead halide perovskite, and then they used a common nanofabrication technique combined with anion exchange chemistry to swap out the halide ions to create cesium lead iodide, cesium lead bromide, and cesium lead chloride perovskites.

    Each variation resulted in a different color emitted. Moreover, the researchers showed that multiple heterojunctions could be engineered on a single nanowire. They were able to achieve a pixel size down to 500 nanometers, and they determined that the color of the material was tunable throughout the entire range of visible light.

    The researchers said that the chemical solution-processing technique used to treat this class of soft, ionic-bonded semiconductors is far simpler than methods used to manufacture traditional colloidal semiconductors.

    “For conventional semiconductors, fabricating the junction is quite complicated and expensive,” said study co-lead author Letian Dou, who conducted the work as a postdoctoral fellow in Yang’s lab. “High temperatures and vacuum conditions are usually involved to control the materials’ growth and doping. Precisely controlling the materials composition and property is also challenging because conventional semiconductors are ‘hard’ due to strong covalent bonding.”

    To swap the anions in a soft semiconductor, the material is soaked in a special chemical solution at room temperature.

    “It’s a simple process, and it is very easy to scale up,” said Yang, who is also a professor of chemistry at UC Berkeley. “You don’t need to spend long hours in a clean room, and you don’t need high temperatures.”

    The researchers are continuing to improve the resolution of these soft semiconductors, and are working to integrate them into an electric circuit.

    Other co-lead authors on this paper are Christopher Kley, UC Berkeley postdoctoral fellow, and Minliang Lai, UC Berkeley graduate student. Dou is now an assistant professor of chemical engineering at Purdue University.

    The DOE Office of Science supported this work.

    See the full article here .

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  • richardmitnick 12:55 pm on June 26, 2017 Permalink | Reply
    Tags: 1T’-WTe2, , , ARPES (or angle-resolved photoemission spectroscopy), , Nanotechnology, NERSC-National Energy Research Scientific Computing Center, Scanning tunneling microscopy, ,   

    From LBNL: “2-D Material’s Traits Could Send Electronics R&D Spinning in New Directions” 

    Berkeley Logo

    Berkeley Lab

    June 26, 2017
    Glenn Roberts Jr
    (510) 486-5582

    This animated rendering shows the atomic structure of a 2-D material known as 1T’-WTe2 that was created and studied at Berkeley Lab’s Advanced Light Source. (Credit: Berkeley Lab.)

    An international team of researchers, working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, fabricated an atomically thin material and measured its exotic and durable properties that make it a promising candidate for a budding branch of electronics known as “spintronics.”

    The material – known as 1T’-WTe2 – bridges two flourishing fields of research: that of so-called 2-D materials, which include monolayer materials such as graphene that behave in different ways than their thicker forms; and topological materials, in which electrons can zip around in predictable ways with next to no resistance and regardless of defects that would ordinarily impede their movement.

    At the edges of this material, the spin of electrons – a particle property that functions a bit like a compass needle pointing either north or south – and their momentum are closely tied and predictable.

    A scanning tunneling microscopy image of a 2-D material created and studied at Berkeley Lab’s Advanced Light Source (orange, background). In the upper right corner, the blue dots represent the layout of tungsten atoms and the red dots represent tellurium atoms. (Credit: Berkeley Lab.)

    This latest experimental evidence could elevate the material’s use as a test subject for next-gen applications, such as a new breed of electronic devices that manipulate its spin property to carry and store data more efficiently than present-day devices. These traits are fundamental to spintronics.

    The material is called a topological insulator because its interior surface does not conduct electricity, and its electrical conductivity (the flow of electrons) is restricted to its edges.

    “This material should be very useful for spintronics studies,” said Sung-Kwan Mo, a physicist and staff scientist at Berkeley Lab’s Advanced Light Source (ALS) who co-led the study, published today in Nature Physics.


    “We’re excited about the fact that we have found another family of materials where we can both explore the physics of 2-D topological insulators and do experiments that may lead to future applications,” said Zhi-Xun Shen, a professor in Physical Sciences at Stanford University and the Advisor for Science and Technology at SLAC National Accelerator Laboratory who also co-led the research effort.

    “This general class of materials is known to be robust and to hold up well under various experimental conditions, and these qualities should allow the field to develop faster,” he added.

    The material was fabricated and studied at the ALS, an X-ray research facility known as a synchrotron. Shujie Tang, a visiting postdoctoral researcher at Berkeley Lab and Stanford University, and a co-lead author in the study, was instrumental in growing 3-atom-thick crystalline samples of the material in a highly purified, vacuum-sealed compartment at the ALS, using a process known as molecular beam epitaxy.

    The high-purity samples were then studied at the ALS using a technique known as ARPES (or angle-resolved photoemission spectroscopy), which provides a powerful probe of materials’ electron properties.

    Beamline 10.0.1 at Berkeley Lab’s Advanced Light Source enables researchers to both create and study atomically thin materials. (Credit: Roy Kaltschmidt/Berkeley Lab.)

    “After we refined the growth recipe, we measured it with ARPES. We immediately recognized the characteristic electronic structure of a 2-D topological insulator,” Tang said, based on theory and predictions. “We were the first ones to perform this type of measurement on this material.”

    But because the conducting part of this material, at its outermost edge, measured only a few nanometers thin – thousands of times thinner than the X-ray beam’s focus – it was difficult to positively identify all of the material’s electronic properties.

    So collaborators at UC Berkeley performed additional measurements at the atomic scale using a technique known as STM, or scanning tunneling microscopy. “STM measured its edge state directly, so that was a really key contribution,” Tang said.

    The research effort, which began in 2015, involved more than two dozen researchers in a variety of disciplines. The research team also benefited from computational work at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC).

    NERSC Cray Cori II supercomputer

    LBL NERSC Cray XC30 Edison supercomputer

    Two-dimensional materials have unique electronic properties that are considered key to adapting them for spintronics applications, and there is a very active worldwide R&D effort focused on tailoring these materials for specific uses by selectively stacking different types.

    “Researchers are trying to sandwich them on top of each other to tweak the material as they wish – like Lego blocks,” Mo said. “Now that we have experimental proof of this material’s properties, we want to stack it up with other materials to see how these properties change.”

    A typical problem in creating such designer materials from atomically thin layers is that materials typically have nanoscale defects that can be difficult to eliminate and that can affect their performance. But because 1T’-WTe2 is a topological insulator, its electronic properties are by nature resilient.

    “At the nanoscale it may not be a perfect crystal,” Mo said, “but the beauty of topological materials is that even when you have less than perfect crystals, the edge states survive. The imperfections don’t break the key properties.”

    Going forward, researchers aim to develop larger samples of the material and to discover how to selectively tune and accentuate specific properties. Besides its topological properties, its “sister materials,” which have similar properties and were also studied by the research team, are known to be light-sensitive and have useful properties for solar cells and for optoelectronics, which control light for use in electronic devices.

    The ALS and NERSC are DOE Office of Science User Facilities. Researchers from Stanford University, the Chinese Academy of Sciences, Shanghai Tech University, POSTECH in Korea, and Pusan National University in Korea also participated in this study. This work was supported by the Department of Energy’s Office of Science, the National Science Foundation, the National Science Foundation of China, the National Research Foundation (NRF) of Korea, and the Basic Science Research Program in Korea.

    See the full article here .

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  • richardmitnick 10:24 am on June 23, 2017 Permalink | Reply
    Tags: , , , , Bragg Projection Ptychography, Crystal lattice of nanoscale materials, Hard X-ray Nanoprobe (HXN) beamline at NSLS-II, Nanotechnology, Stephan Hruszkewycz,   

    From BNL- “National Synchrotron Light Source II User Profile: Stephan Hruszkewycz” 

    Brookhaven Lab

    June 19, 2017
    Laura Mgrdichian

    Stephan Hruszkewycz. No image credit.

    Stephan Hruskewycz is an assistant physicist in the Materials Science Division at the U.S. Department of Energy’s (DOE) Argonne National Laboratory.

    While he regularly conducts research at Argonne’s own synchrotron user facility, the Advanced Photon Source (APS), his work on the nanoscale structure and behavior of materials has led him to book beamtime at the DOE’s newest synchrotron, the National Synchrotron Light Source II (NSLS-II). Both NSLS-II and APS are DOE Office of Science User Facilities.





    What are you studying at NSLS-II?

    The focus of our NSLS-II experiments has been to image defects and imperfections in the crystal lattice of nanoscale materials using a new imaging technique known as Bragg Projection Ptychography. Specifically, we have been studying stacking faults in nanowires made of III-V semiconductors, a class of semiconductor that results from the combination of elements from column III on the periodic table (mainly aluminum, gallium, and indium) and column V (nitrogen, phosphorous, arsenic, and antimony). These materials have properties that make them excellent for certain applications; for example, solar cells made of III-V cells are very efficient.

    During our next run, we will be imaging strain fields in complex oxide thin-film nanostructures. These classes of materials have potential uses for energy conversion in solar and fuel cell applications, and their nanoscale structure plays a large role in performance. By studying these structures in detail, we may be able to figure out how to make these materials perform better.

    Why is NSLS-II is particularly suited to your work?

    The Hard X-ray Nanoprobe (HXN) beamline at NSLS-II delivers a coherent hard x-ray beam focused to a few tens of nanometers and the ability to rotate the sample and detector to enable Bragg diffraction with a nanofocused beam. We are capitalizing on the coherence and stability of the focused beam to convert a series of Bragg diffraction patterns measured from different overlapping positions of the sample into an image of the lattice structure inside a specific region of the crystal. The result provides an image with a resolution down to just a few nanometers, as well as picometer-level sensitivity to lattice distortions.

    Tell us about your background and how you arrived at this field of research.

    I have been interested for some time in developing new methods to exploit coherent hard x-rays to reveal of the structure and dynamics of materials. Recently, I have focused on applying these methods to materials with inhomogeneous internal lattice structures that dictate their overall properties, such as nanostructured oxide thin films and semiconductors. To me, this is an exciting area of research, one where cutting-edge materials science questions can be answered with new x-ray imaging methods at state-of-the-art synchrotron sources that deliver highly coherent beams.

    Who else is involved in this work?

    So far, I have been joined at NSLS-II by Megan Hill, a graduate student in Northwestern University’s Materials Science and Engineering Department; Martin Holt, a staff scientist in Argonne’s Center for Nanoscale Materials; and Brian Stephenson, a senior physicist in Argonne’s Materials Science Division.

    See the full article here .

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

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