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  • richardmitnick 9:13 am on September 14, 2017 Permalink | Reply
    Tags: , , Nanotechnology, Optical information processing, , Plasmonic cavity,   

    From Sandia: “Nanotechnology experts at Sandia create first terahertz-speed polarization optical switch” 


    Sandia Lab

    A Sandia National Laboratories-led team has for the first time used optics rather than electronics to switch a nanometer-thick thin film device from completely dark to completely transparent, or light, at a speed of trillionths of a second.

    The team led by principal investigator Igal Brener published a Nature Photonics paper this spring with collaborators at North Carolina State University. The paper describes work on optical information processing, such as switching or light polarization control using light as the control beam, at terahertz speeds, a rate much faster than what is achievable today by electronic means, and a smaller overall device size than other all-optical switching technologies.

    Electrons spinning around inside devices like those used in telecommunications equipment have a speed limit due to a slow charging rate and poor heat dissipation, so if significantly faster operation is the goal, electrons might have to give way to photons.

    To use photons effectively, the technique requires a device that goes from completely light to completely dark at terahertz speeds. In the past, researchers couldn’t get the necessary contrast change from an optical switch at the speed needed in a small device. Previous attempts were more like dimming a light than turning it off, or required light to travel a long distance.

    The breakthrough shows it’s possible to do high contrast all-optical switching in a very thin device, in which light intensity or polarization is switched optically, said Yuanmu Yang, a former Sandia Labs postdoctoral employee who worked at the Center for Integrated Nanotechnologies, a Department of Energy user facility jointly operated by Sandia and Los Alamos national laboratories. The work was done at CINT.

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    Former Sandia National Laboratories postdoctoral researcher Yuanmu Yang, left, and Sandia researcher Igal Brener set up to do testing in an optical lab. A team led by Brener published a Nature Photonics paper describing work on optical information processing at terahertz speeds, a rate much faster than what is achievable today by electronic means. (Photo by Randy Montoya)

    “Instead of switching a current on and off, the goal would be to switch light on and off at rates much faster than what is achievable today,” Yang said.

    Faster information processing important in communications, physics research

    A very rapid and compact switching platform opens up a new way to investigate fundamental physics problems. “A lot of physical processes actually occur at a very fast speed, at a rate of a few terahertz,” Yang said. “Having this tool lets us study the dynamics of physical processes like molecular rotation and magnetic spin. It’s important for research and for moving knowledge further along.”

    It also could act as a rapid polarization switch — polarization changes the characteristics of light — that could be used in biological imaging or chemical spectroscopy, Brener said. “Sometimes you do measurements that require changing the polarization of light at a very fast rate. Our device can work like that too. It’s either an absolute switch that turns on and off or a polarization switch that just switches the polarization of light.”

    Ultrafast information processing “matters in computing, telecommunications, signal processing, image processing and in chemistry and biology experiments where you want very fast switching,” Brener said. “There are some laser-based imaging techniques that will benefit from having fast switching too.”

    The team’s discovery arose from research funded by the Energy Department’s Basic Energy Sciences, Division of Materials Sciences and Engineering, that, among other things, lets Sandia study light-matter interaction and different concepts in nanophotonics.

    “This is an example where it just grew organically from fundamental research into something that has an amazing performance,” Brener said. “Also, we were lucky that we had a collaboration with North Carolina State University. They had the material and we realized that we could use it for this purpose. It wasn’t driven by an applied project; it was the other way around.”

    The collaboration was funded by Sandia’s Laboratory Directed Research and Development program.

    Technique uses laser beams to carry information, switch device

    The technique uses two laser beams, one carrying the information and the second switching the device on and off.

    The switching beam uses photons to heat up electrons inside semiconductors to temperatures of a few thousand degrees Fahrenheit, which doesn’t cause the sample to get that hot but dramatically changes the material’s optical properties. The material also relaxes at terahertz speeds, in a few hundred femtoseconds or in less than one trillionth of a second. “So we can switch this material on and off at a rate of a few trillion times per second,” Yang said.

    Sandia researchers turn the optical switch on and off by creating something called a plasmonic cavity, which confines light within a few tens of nanometers, and significantly boosts light-matter interaction. By using a special plasmonic material, doped cadmium oxide from North Carolina State, they built a high-quality plasmonic cavity. Heating up electrons in the doped cadmium oxide drastically modifies the opto-electrical properties of the plasmonics cavity, modulating the intensity of the reflected light.

    Traditional plasmonic materials like gold or silver are barely sensitive to the optical control beam. Shining a beam onto them doesn’t change their properties from light to dark or vice versa. The optical control beam, however, alters the doped cadmium oxide cavity very rapidly, controlling its optical properties like an on-off switch.

    The next step is figuring out how to use electrical pulses rather than optical pulses to activate the switch, since an all-optical approach still requires large equipment, Brener said. He estimates the work could take three to five years.

    “For practical purposes, you need to miniaturize and do this electrically,” he said.

    The paper’s authors are Yang, Brener, Salvatore Campione, Willie Luk and Mike Sinclair at Sandia Labs and Jon-Paul Maria, Kyle Kelley and Edward Sachet at North Carolina State.

    See the full article here .

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    Sandia Campus
    Sandia National Laboratory

    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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  • richardmitnick 12:35 pm on September 11, 2017 Permalink | Reply
    Tags: , First On-chip Nanoscale Optical Quantum Memory Developed, Nanotechnology,   

    From Caltech: “First On-chip Nanoscale Optical Quantum Memory Developed” 

    Caltech Logo

    Caltech

    09/11/2017

    Robert Perkins
    (626) 395-1862
    rperkins@caltech.edu

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    Artist’s representation of Faraon’s quantum memory device. Credit: Ella Maru Studio

    Smallest-yet optical quantum memory device is a storage medium for optical quantum networks with the potential to be scaled up for commercial use.

    For the first time, an international team led by engineers at Caltech has developed a computer chip with nanoscale optical quantum memory.

    Quantum memory stores information in a similar fashion to the way traditional computer memory does, but on individual quantum particles—in this case, photons of light. This allows it to take advantage of the peculiar features of quantum mechanics (such as superposition, in which a quantum element can exist in two distinct states simultaneously) to store data more efficiently and securely.

    “Such a device is an essential component for the future development of optical quantum networks that could be used to transmit quantum information,” says Andrei Faraon (BS ’04), assistant professor of applied physics and materials science in the Division of Engineering and Applied Science at Caltech, and the corresponding author of a paper describing the new chip.

    The study appeared online ahead of publication by Science magazine on August 31.

    “This technology not only leads to extreme miniaturization of quantum memory devices, it also enables better control of the interactions between individual photons and atoms,” says Tian Zhong, lead author of the study and a Caltech postdoctoral scholar. Zhong is also an acting assistant professor of molecular engineering at the University of Chicago, where he will set up a laboratory to develop quantum photonic technologies in March 2018.

    The use of individual photons to store and transmit data has long been a goal of engineers and physicists because of their potential to carry information reliably and securely. Because photons lack charge and mass, they can be transmitted across a fiber optic network with minimal interactions with other particles.

    The new quantum memory chip is analogous to a traditional memory chip in a computer. Both store information in a binary code. With traditional memory, information is stored by flipping billions of tiny electronic switches either on or off, representing either a 1 or a 0. That 1 or 0 is known as a bit. By contrast, quantum memory stores information via the quantum properties of individual elementary particles (in this case, a light particle). A fundamental characteristic of those quantum properties—which include polarization and orbital angular momentum—is that they can exist in multiple states at the same time. This means that a quantum bit (known as a qubit) can represent a 1 and a 0 at the same time.

    To store photons, Faraon’s team created memory modules using optical cavities made from crystals doped with rare-earth ions. Each memory module is like a miniature racetrack, measuring just 700 nanometers wide by 15 microns long—on the scale of a red blood cell. Each module was cooled to about 0.5 Kelvin—just above Absolute Zero (0 Kelvin, or -273.15 Celsius)—and then a heavily filtered laser pumped single photons into the modules. Each photon was absorbed efficiently by the rare-earth ions with the help of the cavity.

    The photons were released 75 nanoseconds later, and checked to see whether they had faithfully retained the information recorded on them. Ninety-seven percent of the time, they had, Faraon says.

    Next, the team plans to extend the time that the memory can store information, as well as its efficiency. To create a viable quantum network that sends information over hundreds of kilometers, the memory will need to accurately store data for at least one millisecond. The team also plans to work on ways to integrate the quantum memory into more complex circuits, taking the first steps toward deploying this technology in quantum networks.

    The study is titled “Nanophotonic rare-earth quantum memory with optically controlled retrieval.” Other Caltech coauthors include postdoctoral researcher John G. Bartholomew; graduate students Jonathan M. Kindem (MS ’17), Jake Rochman, and Ioana Craiciu (MS ’17); and former graduate student Evan Miyazono (MS ’15, PhD ’17). Additional authors are from the University of Verona in Italy; the University of Parma in Italy; the National Institute of Standards and Technology in Colorado; and the Jet Propulsion Laboratory, which is managed for NASA by Caltech. This research was funded by the National Science Foundation, the Air Force Office of Scientific Research, and the Defense Advanced Research Projects Agency.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 8:03 am on September 1, 2017 Permalink | Reply
    Tags: , , Nanocrystals rapidly forming superlattices while they are themselves still growing, Nanotechnology, , Scientists Watch ‘Artificial Atoms’ Assemble into Perfect Lattices with Many Uses, , Superlattices can form superfast   

    From SLAC: “Scientists Watch ‘Artificial Atoms’ Assemble into Perfect Lattices with Many Uses” 


    SLAC Lab

    July 31, 2017
    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282
    Written by Glennda Chui

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    An illustration shows nanocrystals assembling into an ordered ‘superlattice’ – a process that a SLAC/Stanford team was able to observe in real time with X-rays from the Stanford Synchrotron Radiation Lightsource (SSRL). They discovered that this assembly takes just a few seconds when carried out in hot solutions. The results open the door for rapid self-assembly of nanocrystal building blocks into complex structures with applications in optoelectronics, solar cells, catalysis and magnetic materials. (Greg Stewart/SLAC National Accelerator Laboratory)

    A serendipitous discovery lets researchers spy on this self-assembly process for the first time with SLAC’s X-ray synchrotron. What they learn will help them fine-tune precision materials for electronics, catalysis and more.

    Some of the world’s tiniest crystals are known as “artificial atoms” because they can organize themselves into structures that look like molecules, including “superlattices” that are potential building blocks for novel materials.

    Now scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have made the first observation of these nanocrystals rapidly forming superlattices while they are themselves still growing. What they learn will help scientists fine-tune the assembly process and adapt it to make new types of materials for things like magnetic storage, solar cells, optoelectronics and catalysts that speed chemical reactions.

    The key to making it work was the serendipitous discovery that superlattices can form superfast – in seconds rather than the usual hours or days – during the routine synthesis of nanocrystals. The scientists used a powerful beam of X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) to observe the growth of nanocrystals and the rapid formation of superlattices in real time.

    SLAC/SSRL

    A paper describing the research, which was done in collaboration with scientists at the DOE’s Argonne National Laboratory, was published today in Nature.

    “The idea is to see if we can get an independent understanding of how these superlattices grow so we can make them more uniform and control their properties,” said Chris Tassone, a staff scientist at SSRL who led the study with Matteo Cargnello, assistant professor of chemical engineering at Stanford.

    Tiny Crystals with Outsized Properties

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    Stanford Assistant Professor Matteo Cargnello at a lab in the Stanford Chemical Engineering Department where nanocrystals are grown. Cargnello and Chris Tassone, a staff scientist at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), led a team that discovered how superlattices can grow unexpectedly fast – in seconds, rather than hours or days – during routine nanocrystal synthesis. (Dawn Harmer/SLAC National Accelerator Laboratory)

    Scientists have been making nanocrystals in the lab since the 1980s. Because of their tiny size –they’re billionths of a meter wide and contain just 100 to 10,000 atoms apiece — they are governed by the laws of quantum mechanics, and this gives them interesting properties that can be changed by varying their size, shape and composition. For instance, spherical nanocrystals known as quantum dots, which are made of semiconducting materials, glow in colors that depend on their size; they are used in biological imaging and most recently in high-definition TV displays.

    In the early 1990s, researchers started using nanocrystals to build superlattices, which have the ordered structure of regular crystals, but with small particles in place of individual atoms. These, too, are expected to have unusual properties that are more than the sum of their parts.

    But until now, superlattices have been grown slowly at low temperatures, sometimes in a matter of days.

    That changed in February 2016, when Stanford postdoctoral researcher Liheng Wu serendipitously discovered that the process can occur much faster than scientists had thought.

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    The experimental set-up at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) where scientists used an X-ray beam to observe superlattices forming during the synthesis of nanocrystals for the first time. The vessel where the reactions took place is at bottom center, wrapped in gold heating tape that boosted the temperature inside to more than 230 degrees Celsius. (Liheng Wu/Stanford University)

    ‘Something Weird Is Happening’

    He was trying to make nanocrystals of palladium – a silvery metal that’s used to promote chemical reactions in catalytic converters and many industrial processes – by heating a solution containing palladium atoms to more than 230 degrees Celsius. The goal was to understand how these tiny particles form, so their size and other properties could be more easily adjusted.

    The team added small windows to a reaction chamber about the size of a tangerine so they could shine an SSRL X-ray beam through it and watch what was happening in real time.

    “It’s kind of like cooking,” Cargnello explained. “The reaction chamber is like a pan. We add a solvent, which is like the frying oil; the main ingredients for the nanocrystals, such as palladium; and condiments, which in this case are surfactant compounds that tune the reaction conditions so you can control the size and composition of the particles. Once you add everything to the pan, you heat it up and fry your stuff.”

    Wu and Stanford graduate student Joshua Willis expected to see the characteristic pattern made by X-rays scattering off the tiny particles. They saw a completely different pattern instead.

    “So something weird is happening,” they texted their adviser.

    The something weird was that the palladium nanocrystals were assembling into superlattices.

    A Balance of Forces

    At this point, “The challenge was to understand what brings the particles together and attracts them to each other but not too strongly, so they have room to wiggle around and settle into an ordered position,” said Jian Qin, an assistant professor of chemical engineering at Stanford who performed theoretical calculations to better understand the self-assembly process.

    Once the nanocrystals form, what seems to be happening is that they acquire a sort of hairy coating of surfactant molecules. The nanocrystals glom together, attracted by weak forces between their cores, and then a finely tuned balance of attractive and repulsive forces between the dangling surfactant molecules holds them in just the right configuration for the superlattice to grow.

    To the scientists’ surprise, the individual nanocrystals then kept on growing, along with the superlattices, until all the chemical ingredients in the solution were used up, and this unexpected added growth made the material swell. The researchers said they think this occurs in a wide range of nanocrystal systems, but had never been seen because there was no way to observe it in real time before the team’s experiments at SSRL.

    “Once we understood this system, we realized this process may be more general than we initially thought,” Wu said. “We have demonstrated that it’s not only limited to metals, but it can also be extended to semiconducting materials and very likely to a much larger set of materials.”

    The team has been doing follow-up experiments to find out more about how the superlattices grow and how they can tweak the size, composition and properties of the finished product.

    Ian Salmon McKay, a graduate student in chemical engineering at Stanford, and Benjamin T. Diroll, a postdoctoral researcher at Argonne National Laboratory’s Center for Nanoscale Materials (CNM), also contributed to the work.

    SSRL and CNM are DOE Office of Science User Facilities. The research was funded by the DOE Office of Science and by a Laboratory Directed Research and Development grant from SLAC.

    See the full article here .

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    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 8:33 am on August 28, 2017 Permalink | Reply
    Tags: , , Berkeley Lab’s Molecular Foundry, , Exciton effect, , Moly sulfide, Nanotechnology, New Results Reveal High Tunability of 2-D Material, Photoluminescence excitation (PLE) spectroscopy,   

    From LBNL: “New Results Reveal High Tunability of 2-D Material” 

    Berkeley Logo

    Berkeley Lab

    August 25, 2017
    Glenn Roberts Jr
    geroberts@lbl.gov
    (510) 486-5582

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    From left: Kaiyuan Yao, Nick Borys, and P. James Schuck, seen here at Berkeley Lab’s Molecular Foundry, measured a property in a 2-D material that could help realize new applications. (Credit: Marilyn Chung/Berkeley Lab)

    Two-dimensional materials are a sort of a rookie phenom in the scientific community. They are atomically thin and can exhibit radically different electronic and light-based properties than their thicker, more conventional forms, so researchers are flocking to this fledgling field to find ways to tap these exotic traits.

    Applications for 2-D materials range from microchip components to superthin and flexible solar panels and display screens, among a growing list of possible uses. But because their fundamental structure is inherently tiny, they can be tricky to manufacture and measure, and to match with other materials. So while 2-D materials R&D is on the rise, there are still many unknowns about how to isolate, enhance, and manipulate their most desirable qualities.

    Now, a science team at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has precisely measured some previously obscured properties of moly sulfide, a 2-D semiconducting material also known as molybdenum disulfide or MoS2. The team also revealed a powerful tuning mechanism and an interrelationship between its electronic and optical, or light-related, properties.

    To best incorporate such monolayer materials into electronic devices, engineers want to know the “band gap,” which is the minimum energy level it takes to jolt electrons away from the atoms they are coupled to, so that they flow freely through the material as electric current flows through a copper wire. Supplying sufficient energy to the electrons by absorbing light, for example, converts the material into an electrically conducting state.

    As reported in the Aug. 25 issue of Physical Review Letters, researchers measured the band gap for a monolayer of moly sulfide, which has proved difficult to accurately predict theoretically, and found it to be about 30 percent higher than expected based on previous experiments. They also quantified how the band gap changes with electron density – a phenomenon known as “band gap renormalization.”

    “The most critical significance of this work was in finding the band gap,” said Kaiyuan Yao, a graduate student researcher at Berkeley Lab and the University of California, Berkeley, who served as the lead author of the research paper.

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    This diagram shows a triangular sample of monolayer moly sulfide (dark blue) on silicon-based layers (light blue and green) during an experimental technique known as photoluminescence excitation spectroscopy. (Credit: Berkeley Lab)

    “That provides very important guidance to all of the optoelectronic device engineers. They need to know what the band gap is” in orderly to properly connect the 2-D material with other materials and components in a device, Yao said.

    Obtaining the direct band gap measurement is challenged by the so-called “exciton effect” in 2-D materials that is produced by a strong pairing between electrons and electron “holes” ­– vacant positions around an atom where an electron can exist. The strength of this effect can mask measurements of the band gap.

    Nicholas Borys, a project scientist at Berkeley Lab’s Molecular Foundry who also participated in the study, said the study also resolves how to tune optical and electronic properties in a 2-D material.

    “The real power of our technique, and an important milestone for the physics community, is to discern between these optical and electronic properties,” Borys said.

    The team used several tools at the Molecular Foundry, a facility that is open to the scientific community and specializes in the creation and exploration of nanoscale materials.

    The Molecular Foundry technique that researchers adapted for use in studying monolayer moly sulfide, known as photoluminescence excitation (PLE) spectroscopy, promises to bring new applications for the material within reach, such as ultrasensitive biosensors and tinier transistors, and also shows promise for similarly pinpointing and manipulating properties in other 2-D materials, researchers said.

    The research team measured both the exciton and band gap signals, and then detangled these separate signals. Scientists observed how light was absorbed by electrons in the moly sulfide sample as they adjusted the density of electrons crammed into the sample by changing the electrical voltage on a layer of charged silicon that sat below the moly sulfide monolayer.

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    This image shows a slight “bump” (red arrow) in charted experimental data that reveals the band gap measurement in a 2-D material known as moly sulfide. (Credit: Berkeley Lab)

    Researchers noticed a slight “bump” in their measurements that they realized was a direct measurement of the band gap, and through a slew of other experiments used their discovery to study how the band gap was readily tunable by simply adjusting the density of electrons in the material.

    “The large degree of tunability really opens people’s eyes,” said P. James Schuck, who was director of the Imaging and Manipulation of Nanostructures facility at the Molecular Foundry during this study.

    “And because we could see both the band gap’s edge and the excitons simultaneously, we could understand each independently and also understand the relationship between them,” said Schuck, who is now at Columbia University. “It turns out all of these properties are dependent on one another.”

    4
    Kaiyuan Yao works with equipment at Berkeley Lab’s Molecular Foundry that was used to help measure a property in a 2-D material. (Credit: Marilyn Chung/Berkeley Lab)

    Moly sulfide, Schuck also noted, is “extremely sensitive to its local environment,” which makes it a prime candidate for use in a range of sensors. Because it is highly sensitive to both optical and electronic effects, it could translate incoming light into electronic signals and vice versa.

    Schuck said the team hopes to use a suite of techniques at the Molecular Foundry to create other types of monolayer materials and samples of stacked 2-D layers, and to obtain definitive band gap measurements for these, too. “It turns out no one yet knows the band gaps for some of these other materials,” he said.

    The team also has expertise in the use of a nanoscale probe to map the electronic behavior across a given sample.

    Borys added, “We certainly hope this work seeds further studies on other 2-D semiconductor systems.”

    The Molecular Foundry is a DOE Office of Science User Facility that provides free access to state-of-the-art equipment and multidisciplinary expertise in nanoscale science to visiting scientists.

    Researchers from the Kavli Energy NanoSciences Institute at UC Berkeley and Berkeley Lab, and from Arizona State University also participated in this study, which was supported by the National Science Foundation.

    See the full article here .

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  • richardmitnick 11:39 am on August 25, 2017 Permalink | Reply
    Tags: Dr Singh Ahluwalia, , , , Nanotechnology, Next-gen nanoscopes can take super-res images of the atomic world, Photonic circuits could offer researchers a cost-effective way to delve deeper into the nano world,   

    From Horizon: “Next-gen nanoscopes can take super-res images of the atomic world – Dr Singh Ahluwalia” 

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    Horizon

    23 August 2017
    Lou Del Bello

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    Compact photonic chips will be able to be used with any standard optical microscope. Image credit – Geir Antonsen

    With some nanoscopes costing €1 million it’s not cheap examining the world at an atomic level, but according to Dr Balpreet Singh Ahluwalia, from the Arctic University of Norway, photonic circuits could offer researchers a cost-effective way to delve deeper into the nano world.

    Nanoscopy is still a relatively young research field, but the technology you developed is already revolutionising it. Can you tell us a bit more about your invention?

    ‘For the past 150 years people believed that microscopes cannot see images below 200 nanometres. They thought that was an established fact – all the new knowledge in the field has been acquired.

    ‘In 2007, when I started working on my idea, nanoscopy was still in its infancy so the timing was right to try new things. Today, I successfully introduced a cheap and more effective alternative to the conventional nanoscopes currently available, which can cost between €500 000 and €1 million.’

    How exactly does your alternative nanoscope work?

    ‘Currently, advanced microscopes are complex and costly. They are used to shape and deliver the specialised laser illumination patterns required to achieve high-resolution images.

    ‘In this type of microscope, the sample is placed on top of a simple glass slide or cover slip. I proposed an inverse solution, where the sample is placed on top of a complex photonic chip and images are acquired using a standard optical microscope. The photonic chip is used both to hold the sample, like a glass cover slide, and to deliver the required illumination pattern to achieve the super-resolution images.

    ‘This alleviates the need for sophisticated laser illumination and consequently any standard optical microscope can be used with our photonic chip. Integrated photonic chips can also be used to generate any exotic set of illumination patterns, which is very difficult to achieve with conventional solutions.

    ‘Our long-term goal is to retrofit the highest possible number of standard optical microscopes with the novel photonic chip and convert them into high-resolution optical nanoscopes.’

    Your chip is smaller and more manageable than any other nanoscope, but how is it also cheaper?

    ‘These photonic chips can be mass produced by semi-conductor foundries (factories) and are similar to silicon chips that are inside our mobile phones. Therefore, their cost is significantly lower, within the tens of euros.

    ‘We hope that this advantage will increase the penetration of optical nanoscopy to the developing world. In research environments where resources are limited, most labs are equipped with low-quality optical microscopes because the upfront costs of nanoscopes are prohibitive.’

    You said that your photonic chip is not only a cheaper alternative to laser nanoscopes, but also more effective. What applications could it lead to?

    ‘Besides being more compact, stable and affordable, our chip-based nanoscope also captures images over extremely large fields of view. It can acquire super-resolved images from a field of view 100 times larger than what can be presently achieved using commercial optical nanoscopy systems.

    ‘This could prove a game-changer in fields such as pathology, where you have to analyse samples with a surface of several square millimetres. An average optical microscope will scan an area of 50 microns at a time, so it would take days to scan an entire pathology sample (such as tissue, blood or urine).

    ‘Our local research team, in collaboration with the medical department, is currently working on the liver, trying to understand how filtration within the cells works. Until now, this could not be done because the specialised cells have small holes, or nanoholes, which are around 50-200 nanometres wide. You can’t see that with a normal microscope.’

    Your research was part of an EU-funded project called NANOSCOPY – do you have a business plan to scale-up your innovation?

    ‘I was lucky to have the right financial support from the EU’s European Research Council (ERC) that chose to invest in my high-risk, high-return research project.

    ‘We are now in touch with potential manufacturers, and our business case is strong. Imagine a coffee machine – the customer only needs to replace the coffee, which is much cheaper than buying a brand new machine every time you fancy an espresso.

    ‘So it’s the same principle, the initial barrier to the technology is very low, compared to what exists at the moment. Until now you had to have EUR 500 000 to buy a nanoscope, but now you just need to add a chip to your inexpensive microscope and adapt the laser input.’

    Does your scientific approach come from your background or a particular experience in your life?

    ‘My personal journey has left me with the very strong belief that the place where you work or study is not important, the people are important. I studied different subjects in various labs all over the world, and the teams I met along the way provided a unique mix of perspectives on any scientific dilemma.

    ‘I grew up in a small town in India called Varanasi, also called Kashi, it is the oldest city of India – it’s very ancient with a very distinctive culture. My mother always told me that scientists travel a lot and have an adventurous life which gives them opportunities to also help people. During my university studies I was sure that I wanted to be a researcher, but I did not have the possibility to study in the US like most Indian students who want to further their education abroad, because after the 9/11 terror attacks the frontiers were closed for a while. So I chose to study in Singapore first and did my PhD at Nanyang Technological University (Singapore), after that I relocated to Norway and had lived and worked for a one year in the UK and USA. Presently, I work in Norway where I fell in love with Europe.

    ‘While my somehow unconventional career path led me to see a problem through a creative lens, much of my success has been made possible by the very diverse group that we have (here in Norway). Our group includes people from almost all the continents, from Asia to Africa and the Americas. We have researchers with a chemistry background, pure biology, from bio-optics, physics and engineering. So we have a multidisciplinary group as well as a multi-ethnic group and I think it’s very important because we need people with diverse expertise to curate various sides of the project.’

    See the full article here .

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  • richardmitnick 10:11 am on August 11, 2017 Permalink | Reply
    Tags: , , Modulating semiconductors, Nanotechnology,   

    From BNL: “Scientists Find New Method to Control Electronic Properties of Nanocrystals” 

    Brookhaven Lab

    August 10, 2017
    Stephanie Kossman

    1
    From Left to Right: XPD beamline scientist Sanjit Ghose, postdoctoral researcher Anna Plonka, and Brookhaven Chemist Anatoly Frenkel.

    Researchers from The Hebrew University of Jerusalem, Stony Brook University, and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have discovered new effects of an important method for modulating semiconductors. The method, which works by creating open spaces or “vacancies” in a material’s structure, enables scientists to tune the electronic properties of semiconductor nanocrystals (SCNCs)—semiconductor particles that are smaller than 100 nanometers. This finding will advance the development of new technologies like smart windows, which can change opaqueness on demand.

    Scientists use a technique called “chemical doping” to control the electronic properties of semiconductors. In this process, chemical impurities—atoms from different materials—are added to a semiconductor in order to alter its electrical conductivity. Though it is possible to dope SCNCs, it is very difficult due to their tiny size. The amount of impurities added during chemical doping is so small that in order to dope a nanocrystal properly, no more than a few atoms can be added to the crystal. Nanocrystals also tend to expel impurities, further complicating the doping process.

    Seeking to control the electronic properties of SCNCs more easily, researchers studied a technique called vacancy formation. In this method, impurities are not added to the semiconductor; instead, vacancies in its structure are formed by oxidation-reduction (redox) reactions, a type of chemical reaction where electrons are transferred between two materials. During this transfer, a type of doping occurs as missing electrons, called holes, become free to move throughout the structure of the crystal, significantly altering the electrical conductivity of the SCNC.

    “We have also identified size effects in the efficiency of the vacancy formation doping reaction,” said Uri Banin, a nanotechnologist from the Hebrew University of Jerusalem. “Vacancy formation is actually more efficient in larger SCNCs.”

    In this study, the researchers investigated a redox reaction between copper sulfide nanocrystals (the semiconductor) and iodine, a chemical introduced in order to influence the redox reaction to occur.

    2
    (Top) The removal of copper from copper sulfide nanocrystals and the growth of copper iodine on nanocrystal facets is depicted by results from XAFS; (Bottom left) Larger nanocrystals are doped more efficiently by vacancy formation; (Right) Vacancy formation is observed by XRD.

    “If you reduce copper sulfide, you will pull out copper from the nanocrystal, generating vacancies and therefore holes,” said Anatoly Frenkel, a chemist at Brookhaven National Laboratory holding a joint appointment with Stony Brook University, and the lead Brookhaven researcher on this study.

    The researchers used the x-ray powder diffraction (XPD) beamline at the National Synchrotron Light Source II (NSLS-II)—a DOE Office of Science User Facility—to study the structure of copper sulfide during the redox reaction.

    BNL NSLS-II


    BNL NSLS II

    By shining ultra-bright x-rays onto their samples, the researchers are able to determine the amount of copper that is pulled out during the redox reaction.

    Based on their observations at NSLS-II, the team confirmed that adding more iodine to the system caused more copper to be released and more vacancies to form. This established that vacancy formation is a useful technique for tuning the electronic properties of SCNCs.

    Still, the researchers needed to find out what exactly was happening to copper when it left the nanocrystal. Understanding how copper behaves after the redox reaction is crucial for implementing this technique into smart window technology.

    “If copper uncontrollably disappears, we can’t pull it back into the system,” Frenkel said. “But suppose the copper that is taken out of the crystal is hovering around, ready to go back in. By using the reverse process, we can put it back into the system, and we can make a device that would be easy to switch from one state to the other. For example, you would be able to change the transparency of a window on demand, depending on the time of day or your mood.”

    To understand what was happening to copper, the researchers used x-ray absorption fine structure (XAFS) spectroscopy at the Advanced Photon Source (APS)—also a DOE Office of Science User Facility—at Argonne National Laboratory. This technique allows the researchers to study the extremely small copper complexes that x-ray diffraction cannot detect. XAFS revealed that copper was combining with iodine to form copper iodine, a positive result that indicated copper could be put back into the nanocrystal and that the researchers have full control of the electronic properties.

    The researchers say the next step is to study materials in real-time during redox reactions using NSLS-II.

    This study was supported by the National Science Foundation, the US-Israel Binational Science Foundation, and Northwestern University. DOE’s Office of Science also supports operations at NSLS-II and APS.

    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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  • richardmitnick 3:39 pm on August 1, 2017 Permalink | Reply
    Tags: A newly discovered collective rattling effect in a type of crystalline semiconductor blocks most heat transfer while preserving high electrical conductivity, , , , Nanotechnology, , Scanning Electron microscopy   

    From LBNL: “A Semiconductor That Can Beat the Heat” 

    Berkeley Logo

    Berkeley Lab

    July 31, 2017
    Jon Weiner
    jrweiner@lbl.gov
    (510) 486-4014

    A newly discovered collective rattling effect in a type of crystalline semiconductor blocks most heat transfer while preserving high electrical conductivity – a rare pairing that scientists say could reduce heat buildup in electronic devices and turbine engines, among other possible applications.

    A team led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) discovered these exotic traits in a class of materials known as halide perovskites, which are also considered promising candidates for next-generation solar panels, nanoscale lasers, electronic cooling, and electronic displays.

    These interrelated thermal and electrical (or “thermoelectric”) properties were found in nanoscale wires of cesium tin iodide (CsSnI3). The material was observed to have one of the lowest levels of heat conductivity among materials with a continuous crystalline structure.

    1
    Rattling structures of halide perovskites: cesium tin iodide (left) and cesium lead iodide (right). (Credit: Berkeley Lab/UC Berkeley)

    This so-called single-crystal material can also be more easily produced in large quantities than typical thermoelectric materials, such as silicon-germanium, researchers said.

    “Its properties originate from the crystal structure itself. It’s an atomic sort of phenomenon,” said Woochul Lee, a postdoctoral researcher at Berkeley Lab who was the lead author of the study, published the week of July 31 in the Proceedings of the National Academy of Sciences journal. These are the first published results relating to the thermoelectric performance of this single crystal material.

    Researchers earlier thought that the material’s thermal properties were the product of “caged” atoms rattling around within the material’s crystalline structure, as had been observed in some other materials. Such rattling can serve to disrupt heat transfer in a material.

    “We initially thought it was atoms of cesium, a heavy element, moving around in the material,” said Peidong Yang, a senior faculty scientist at Berkeley Lab’s Materials Sciences Division who led the study.

    Jeffrey Grossman, a researcher at the Massachusetts Institute of Technology, then performed some theory work and computerized simulations that helped to explain what the team had observed. Researchers also used Berkeley Lab’s Molecular Foundry, which specializes in nanoscale research, in the study.

    “We believe there is essentially a rattling mechanism, not just with the cesium. It’s the overall structure that’s rattling; it’s a collective rattling,” Yang said. “The rattling mechanism is associated with the crystal structure itself,” and is not the product of a collection of tiny crystal cages. “It is group atomic motion,” he added.

    Within the material’s crystal structure, the distance between atoms is shrinking and growing in a collective way that prevents heat from easily flowing through.

    But because the material is composed of an orderly, single-crystal structure, electrical current can still flow through it despite this collective rattling. Picture its electrical conductivity is like a submarine traveling smoothly in calm underwater currents, while its thermal conductivity is like a sailboat tossed about in heavy seas at the surface.

    Yang said two major applications for thermoelectric materials are in cooling, and in converting heat into electrical current. For this particular cesium tin iodide material, cooling applications such as a coating to help cool electronic camera sensors may be easier to achieve than heat-to-electrical conversion, he said.

    A challenge is that the material is highly reactive to air and water, so it requires a protective coating or encapsulation to function in a device.

    Cesium tin iodide was first discovered as a semiconductor material decades ago, and only in recent years has it been rediscovered for its other unique traits, Yang said. “It turns out to be an amazing gold mine of physical properties,” he noted.

    3
    Scanning electron microscope images of suspended micro-island devices. Individual AIHP NW is suspended between two membranes. (Credit: Berkeley Lab/UC Berkeley).

    To measure the thermal conductivity of the material, researchers bridged two islands of an anchoring material with a cesium tin iodide nanowire. The nanowire was connected at either end to micro-islands that functioned as both a heater and a thermometer. Researchers heated one of the islands and precisely measured how the nanowire transported heat to the other island.

    They also performed scanning electron microscopy to precisely measure the dimensions of the nanowire. They used these dimensions to provide an exacting measure of the material’s thermal conductivity. The team repeated the experiment with several different nanowire materials and multiple nanowire samples to compare thermoelectric properties and verify the thermal conductivity measurements.

    “A next step is to alloy this (cesium tin iodide) material,” Lee said. “This may improve the thermoelectric properties.”

    Also, just as computer chip manufacturers implant a succession of elements into silicon wafers to improve their electronic properties – a process known as “doping” – scientists hope to use similar techniques to more fully exploit the thermoelectric traits of this semiconductor material. This is relatively unexplored territory for this class of materials, Yang said.

    The research team also included other scientists from Berkeley Lab’s Materials Sciences Division and the Molecular Foundry, the Kavli Energy NanoScience Institute at UC Berkeley and Berkeley Lab, and UC Berkeley’s Department of Chemistry.

    The Molecular Foundry is a DOE Office of Science User Facility that provides free access to state-of-the-art equipment and multidisciplinary expertise in nanoscale science to visiting scientists from all over the world.

    This work was supported by the Department of Energy’s Office of Basic Energy Sciences.

    More information about Peidong Yang’s research group: http://nanowires.berkeley.edu/.

    See the full article here .

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  • richardmitnick 11:03 am on July 31, 2017 Permalink | Reply
    Tags: , Nanocrystals, Nanotechnology, , , , Superlattices,   

    From SLAC: “Scientists Watch ‘Artificial Atoms’ Assemble into Perfect Lattices with Many Uses” 


    SLAC Lab

    July 31, 2017
    Written by Glennda Chui

    Press Office Contact:
    Andrew Gordon
    agordon@slac.stanford.edu
    (650) 926-2282

    1
    An illustration shows nanocrystals assembling into an ordered ‘superlattice’ – a process that a SLAC/Stanford team was able to observe in real time with X-rays from the Stanford Synchrotron Radiation Lightsource (SSRL). They discovered that this assembly takes just a few seconds when carried out in hot solutions. The results open the door for rapid self-assembly of nanocrystal building blocks into complex structures with applications in optoelectronics, solar cells, catalysis and magnetic materials. (Greg Stewart/SLAC National Accelerator Laboratory.)

    SLAC/SSRL

    Some of the world’s tiniest crystals are known as “artificial atoms” because they can organize themselves into structures that look like molecules, including “superlattices” that are potential building blocks for novel materials.

    Now scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have made the first observation of these nanocrystals rapidly forming superlattices while they are themselves still growing. What they learn will help scientists fine-tune the assembly process and adapt it to make new types of materials for things like magnetic storage, solar cells, optoelectronics and catalysts that speed chemical reactions.

    The key to making it work was the serendipitous discovery that superlattices can form superfast – in seconds rather than the usual hours or days – during the routine synthesis of nanocrystals. The scientists used a powerful beam of X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) to observe the growth of nanocrystals and the rapid formation of superlattices in real time.

    A paper describing the research, which was done in collaboration with scientists at the DOE’s Argonne National Laboratory, was published today in Nature.

    2
    A lab in the Stanford Chemical Engineering Department where nanocrystals are grown. Experiments at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) were able to observe the simultaneous growth of nanocrystals and superlattices for the first time. (Dawn Harmer/SLAC National Accelerator Laboratory.)

    “The idea is to see if we can get an independent understanding of how these superlattices grow so we can make them more uniform and control their properties,” said Chris Tassone, a staff scientist at SSRL who led the study with Matteo Cargnello, assistant professor of chemical engineering at Stanford.

    Tiny Crystals with Outsized Properties

    Scientists have been making nanocrystals in the lab since the 1980s. Because of their tiny size –they’re billionths of a meter wide and contain just 100 to 10,000 atoms apiece — they are governed by the laws of quantum mechanics, and this gives them interesting properties that can be changed by varying their size, shape and composition. For instance, spherical nanocrystals known as quantum dots, which are made of semiconducting materials, glow in colors that depend on their size; they are used in biological imaging and most recently in high-definition TV displays.

    In the early 1990s, researchers started using nanocrystals to build superlattices, which have the ordered structure of regular crystals, but with small particles in place of individual atoms. These, too, are expected to have unusual properties that are more than the sum of their parts.

    But until now, superlattices have been grown slowly at low temperatures, sometimes in a matter of days.

    That changed in February 2016, when Stanford postdoctoral researcher Liheng Wu serendipitously discovered that the process can occur much faster than scientists had thought.

    3
    The experimental set-up at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) where scientists used an X-ray beam to observe superlattices forming during the synthesis of nanocrystals for the first time. The vessel where the reactions took place is at bottom center, wrapped in gold heating tape that boosted the temperature inside to more than 230 degrees Celsius. (Liheng Wu/Stanford University.)

    ‘Something Weird Is Happening’

    He was trying to make nanocrystals of palladium – a silvery metal that’s used to promote chemical reactions in catalytic converters and many industrial processes – by heating a solution containing palladium atoms to more than 230 degrees Celsius. The goal was to understand how these tiny particles form, so their size and other properties could be more easily adjusted.

    The team added small windows to a reaction chamber about the size of a tangerine so they could shine an SSRL X-ray beam through it and watch what was happening in real time.

    “It’s kind of like cooking,” Cargnello explained. “The reaction chamber is like a pan. We add a solvent, which is like the frying oil; the main ingredients for the nanocrystals, such as palladium; and condiments, which in this case are surfactant compounds that tune the reaction conditions so you can control the size and composition of the particles. Once you add everything to the pan, you heat it up and fry your stuff.”

    Wu and Stanford graduate student Joshua Willis expected to see the characteristic pattern made by X-rays scattering off the tiny particles. They saw a completely different pattern instead.

    “So something weird is happening,” they texted their adviser.

    The something weird was that the palladium nanocrystals were assembling into superlattices.

    4
    Members of the nanocrystal research team, from left: Assistant Professor Jian Qin, postdoctoral researcher Liheng Wu and Assistant Professor Matteo Cargnello, all of Stanford; SLAC staff scientist Chris Tassone; and Stanford graduate student Joshua Willis. (Dawn Harmer/SLAC National Accelerator Laboratory)

    A Balance of Forces

    At this point, “The challenge was to understand what brings the particles together and attracts them to each other but not too strongly, so they have room to wiggle around and settle into an ordered position,” said Jian Qin, an assistant professor of chemical engineering at Stanford who performed theoretical calculations to better understand the self-assembly process.

    Once the nanocrystals form, what seems to be happening is that they acquire a sort of hairy coating of surfactant molecules. The nanocrystals glom together, attracted by weak forces between their cores, and then a finely tuned balance of attractive and repulsive forces between the dangling surfactant molecules holds them in just the right configuration for the superlattice to grow.

    To the scientists’ surprise, the individual nanocrystals then kept on growing, along with the superlattices, until all the chemical ingredients in the solution were used up, and this unexpected added growth made the material swell. The researchers said they think this occurs in a wide range of nanocrystal systems, but had never been seen because there was no way to observe it in real time before the team’s experiments at SSRL.

    “Once we understood this system, we realized this process may be more general than we initially thought,” Wu said. “We have demonstrated that it’s not only limited to metals, but it can also be extended to semiconducting materials and very likely to a much larger set of materials.”

    The team has been doing follow-up experiments to find out more about how the superlattices grow and how they can tweak the size, composition and properties of the finished product.

    Ian Salmon McKay, a graduate student in chemical engineering at Stanford, and Benjamin T. Diroll, a postdoctoral researcher at Argonne National Laboratory’s Center for Nanoscale Materials (CNM), also contributed to the work.

    SSRL and CNM are DOE Office of Science User Facilities. The research was funded by the DOE Office of Science and by a Laboratory Directed Research and Development grant from SLAC.

    See the full article here .

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  • richardmitnick 11:53 am on July 29, 2017 Permalink | Reply
    Tags: 3D structure of human chromatin, , ChromEMT, , , , Nanotechnology, ,   

    From Salk: “Salk scientists solve longstanding biological mystery of DNA organization” 

    Salk Institute bloc

    Salk Institute for Biological Studies

    July 27, 2017

    Stretched out, the DNA from all the cells in our body would reach Pluto. So how does each tiny cell pack a two-meter length of DNA into its nucleus, which is just one-thousandth of a millimeter across?

    The answer to this daunting biological riddle is central to understanding how the three-dimensional organization of DNA in the nucleus influences our biology, from how our genome orchestrates our cellular activity to how genes are passed from parents to children.

    Now, scientists at the Salk Institute and the University of California, San Diego, have for the first time provided an unprecedented view of the 3D structure of human chromatin—the combination of DNA and proteins—in the nucleus of living human cells.

    In the tour de force study, described in Science on July 27, 2017, the Salk researchers identified a novel DNA dye that, when paired with advanced microscopy in a combined technology called ChromEMT, allows highly detailed visualization of chromatin structure in cells in the resting and mitotic (dividing) stages. By revealing nuclear chromatin structure in living cells, the work may help rewrite the textbook model of DNA organization and even change how we approach treatments for disease.

    “One of the most intractable challenges in biology is to discover the higher-order structure of DNA in the nucleus and how is this linked to its functions in the genome,” says Salk Associate Professor Clodagh O’Shea, a Howard Hughes Medical Institute Faculty Scholar and senior author of the paper. “It is of eminent importance, for this is the biologically relevant structure of DNA that determines both gene function and activity.”

    2
    A new technique enables 3D visualization of chromatin (DNA plus associated proteins) structure and organization within a cell nucleus (purple, bottom left) by painting the chromatin with a metal cast and imaging it with electron microscopy (EM). The middle block shows the captured EM image data, the front block illustrates the chromatin organization from the EM data, and the rear block shows the contour lines of chromatin density from sparse (cyan and green) to dense (orange and red). Credit: Salk Institute.

    Ever since Francis Crick and James Watson determined the primary structure of DNA to be a double helix, scientists have wondered how DNA is further organized to allow its entire length to pack into the nucleus such that the cell’s copying machinery can access it at different points in the cell’s cycle of activity. X-rays and microscopy showed that the primary level of chromatin organization involves 147 bases of DNA spooling around proteins to form particles approximately 11 nanometers (nm) in diameter called nucleosomes. These nucleosome “beads on a string” are then thought to fold into discrete fibers of increasing diameter (30, 120, 320 nm etc.), until they form chromosomes. The problem is, no one has seen chromatin in these discrete intermediate sizes in cells that have not been broken apart and had their DNA harshly processed, so the textbook model of chromatin’s hierarchical higher-order organization in intact cells has remained unverified.

    To overcome the problem of visualizing chromatin in an intact nucleus, O’Shea’s team screened a number of candidate dyes, eventually finding one that could be precisely manipulated with light to undergo a complex series of chemical reactions that would essentially “paint” the surface of DNA with a metal so that its local structure and 3D polymer organization could be imaged in a living cell. The team partnered with UC San Diego professor and microscopy expert Mark Ellisman, one of the paper’s coauthors, to exploit an advanced form of electron microscopy that tilts samples in an electron beam enabling their 3D structure to be reconstructed. By combining their chromatin dye with electron-microscope tomography, they created ChromEMT.

    The team used ChromEMT to image and measure chromatin in resting human cells and during cell division when DNA is compacted into its most dense form—the 23 pairs of mitotic chromosomes that are the iconic image of the human genome. Surprisingly, they did not see any of the higher-order structures of the textbook model anywhere.

    3
    From left: Horng Ou and Clodagh O’Shea. Credit: Salk Institute.

    “The textbook model is a cartoon illustration for a reason,” says Horng Ou, a Salk research associate and the paper’s first author. “Chromatin that has been extracted from the nucleus and subjected to processing in vitro—in test tubes—may not look like chromatin in an intact cell, so it is tremendously important to be able to see it in vivo.”

    What O’Shea’s team saw, in both resting and dividing cells, was chromatin whose “beads on a string” did not form any higher-order structure like the theorized 30 or 120 or 320 nanometers. Instead, it formed a semi-flexible chain, which they painstakingly measured as varying continuously along its length between just 5 and 24 nanometers, bending and flexing to achieve different levels of compaction. This suggests that it is chromatin’s packing density, and not some higher-order structure, that determines which areas of the genome are active and which are suppressed.

    With their 3D microscopy reconstructions, the team was able to move through a 250 nm x 1000 nm x 1000 nm volume of chromatin’s twists and turns, and envision how a large molecule like RNA polymerase, which transcribes (copies) DNA, might be directed by chromatin’s variable packing density, like a video game aircraft flying through a series of canyons, to a particular spot in the genome. Besides potentially upending the textbook model of DNA organization, the team’s results suggest that controlling access to chromatin could be a useful approach to preventing, diagnosing and treating diseases such as cancer.

    “We show that chromatin does not need to form discrete higher-order structures to fit in the nucleus,” adds O’Shea. “It’s the packing density that could change and limit the accessibility of chromatin, providing a local and global structural basis through which different combinations of DNA sequences, nucleosome variations and modifications could be integrated in the nucleus to exquisitely fine-tune the functional activity and accessibility of our genomes.”

    Future work will examine whether chromatin’s structure is universal among cell types or even among organisms.

    Other authors included Sébastien Phan, Thomas Deerinck and Andrea Thor of the UC San Diego.

    The work was largely funded by the W. M. Keck Foundation, the NIH 4D Nucleome Roadmap Initiative and the Howard Hughes Medical Institute, with additional support from the William Scandling Trust, the Price Family Foundation and the Leona M. and Harry B. Helmsley Charitable Trust.

    See the full article here .

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    Every cure has a starting point. Like Dr. Jonas Salk when he conquered polio, Salk scientists are dedicated to innovative biological research. Exploring the molecular basis of diseases makes curing them more likely. In an outstanding and unique environment we gather the foremost scientific minds in the world and give them the freedom to work collaboratively and think creatively. For over 50 years this wide-ranging scientific inquiry has yielded life-changing discoveries impacting human health. We are home to Nobel Laureates and members of the National Academy of Sciences who train and mentor the next generation of international scientists. We lead biological research. We prize discovery. Salk is where cures begin.

     
  • richardmitnick 6:07 am on July 21, 2017 Permalink | Reply
    Tags: , , Majorana fermion found, Nanotechnology, ,   

    From Stanford: “An experiment proposed by Stanford theorists finds evidence for the Majorana fermion, a particle that’s its own antiparticle” 

    Stanford University Name
    Stanford University

    July 20, 2017
    Glennda Chui

    Media Contact
    Amy Adams, Stanford News Service:
    (650) 796-3695
    amyadams@stanford.edu

    In 1928, physicist Paul Dirac made the stunning prediction that every fundamental particle in the universe has an antiparticle – its identical twin but with opposite charge. When particle and antiparticle met they would be annihilated, releasing a poof of energy. Sure enough, a few years later the first antimatter particle – the electron’s opposite, the positron – was discovered, and antimatter quickly became part of popular culture.

    But in 1937, another brilliant physicist, Ettore Majorana, introduced a new twist: He predicted that in the class of particles known as fermions, which includes the proton, neutron, electron, neutrino and quark, there should be particles that are their own antiparticles.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Now a team including Stanford scientists says it has found the first firm evidence of such a Majorana fermion.

    1
    Credit: Image courtesy of Stanford University

    It was discovered in a series of lab experiments on exotic materials at the University of California in collaboration with Stanford University. The team was led by UC-Irvine Associate Professor Jing Xia and UCLA Professor Kang Wang, and followed a plan proposed by Shoucheng Zhang, professor of physics at Stanford, and colleagues. The team reported the results July 20 in Science.

    2
    MAJORANAS IN MOTION Majorana fermions (blue, red, and purple lines) travel through a topological insulator (horizontal bar) with a superconductor layered on top in this illustration of new experiments to detect the fermions. Green lines indicate electrons travelling on the edges of the topological insulator. Beijing Sondii Technology Co Ltd.

    “Our team predicted exactly where to find the Majorana fermion and what to look for as its ‘smoking gun’ experimental signature,” said Zhang, a theoretical physicist and one of the senior authors of the research paper. “This discovery concludes one of the most intensive searches in fundamental physics, which spanned exactly 80 years.”

    Although the search for the famous fermion seems more intellectual than practical, he added, it could have real-life implications for building robust quantum computers, although this is admittedly far in the future.

    The particular type of Majorana fermion the research team observed is known as a “chiral” fermion because it moves along a one-dimensional path in just one direction. While the experiments that produced it were extremely difficult to conceive, set up and carry out, the signal they produced was clear and unambiguous, the researchers said.

    “This research culminates a chase for many years to find chiral Majorana fermions. It will be a landmark in the field,” said Tom Devereaux, director of the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC National Accelerator Laboratory, where Zhang is a principal investigator.

    “It does seem to be a really clean observation of something new,” said Frank Wilczek, a theoretical physicist and Nobel laureate at the Massachusetts Institute of Technology who was not involved in the study. “It’s not fundamentally surprising, because physicists have thought for a long time that Majorana fermions could arise out of the types of materials used in this experiment. But they put together several elements that had never been put together before, and engineering things so this new kind of quantum particle can be observed in a clean, robust way is a real milestone.”

    Search for ‘quasiparticles’

    Majorana’s prediction applied only to fermions that have no charge, like the neutron and neutrino. Scientists have since found an antiparticle for the neutron, but they have good reasons to believe that the neutrino could be its own antiparticle, and there are four experiments underway to find out – including EXO-200, the latest incarnation of the Enriched Xenon Observatory, in New Mexico. But these experiments are extraordinarily difficult and are not expected to produce an answer for about a decade.

    About 10 years ago, scientists realized that Majorana fermions might also be created in experiments that explore the physics of materials – and the race was on to make that happen.

    What they’ve been looking for are “quasiparticles” – particle-like excitations that arise out of the collective behavior of electrons in superconducting materials, which conduct electricity with 100 percent efficiency. The process that gives rise to these quasiparticles is akin to the way energy turns into short-lived “virtual” particles and back into energy again in the vacuum of space, according to Einstein’s famous equation E = mc2. While quasiparticles are not like the particles found in nature, they would nonetheless be considered real Majorana fermions.

    Over the past five years, scientists have had some success with this approach, reporting that they had seen promising Majorana fermion signatures in experiments involving superconducting nanowires.

    But in those cases the quasiparticles were “bound” – pinned to one particular place, rather than propagating in space and time – and it was hard to tell if other effects were contributing to the signals researchers saw, Zhang said.

    A ‘smoking gun’

    In the latest experiments at UCLA and UC-Irvine, the team stacked thin films of two quantum materials – a superconductor and a magnetic topological insulator – and sent an electrical current through them, all inside a chilled vacuum chamber.

    The top film was a superconductor. The bottom one was a topological insulator, which conducts current only along its surface or edges but not through its middle. Putting them together created a superconducting topological insulator, where electrons zip along two edges of the material’s surface without resistance, like cars on a superhighway.

    It was Zhang’s idea to tweak the topological insulator by adding a small amount of magnetic material to it. This made the electrons flow one way along one edge of the surface and the opposite way along the opposite edge.

    Then the researchers swept a magnet over the stack. This made the flow of electrons slow, stop and switch direction. These changes were not smooth, but took place in abrupt steps, like identical stairs in a staircase.

    At certain points in this cycle, Majorana quasiparticles emerged, arising in pairs out of the superconducting layer and traveling along the edges of the topological insulator just as the electrons did. One member of each pair was deflected out of the path, allowing the researchers to easily measure the flow of the individual quasiparticles that kept forging ahead. Like the electrons, they slowed, stopped and changed direction – but in steps exactly half as high as the ones the electrons took.

    These half-steps were the smoking gun evidence the researchers had been looking for.

    The results of these experiments are not likely to have any effect on efforts to determine if the neutrino is its own antiparticle, said Stanford physics Professor Giorgio Gratta, who played a major role in designing and planning EXO-200.

    “The quasiparticles they observed are essentially excitations in a material that behave like Majorana particles,” Gratta said. “But they are not elementary particles and they are made in a very artificial way in a very specially prepared material. It’s very unlikely that they occur out in the universe, although who are we to say? On the other hand, neutrinos are everywhere, and if they are found to be Majorana particles we would show that nature not only has made this kind of particles possible but, in fact, has literally filled the universe with them.”

    He added, “Where it gets more interesting is that analogies in physics have proved very powerful. And even if they are very different beasts, different processes, maybe we can use one to understand the other. Maybe we will discover something that is interesting for us, too.”

    Angel particle

    Far in the future, Zhang said, Majorana fermions could be used to construct robust quantum computers that aren’t thrown off by environmental noise, which has been a big obstacle to their development. Since each Majorana is essentially half a subatomic particle, a single qubit of information could be stored in two widely separated Majorana fermions, decreasing the chance that something could perturb them both at once and make them lose the information they carry.

    For now, he suggests a name for the chiral Majorana fermion his team discovered: the “angel particle,” in reference to the best-selling 2000 thriller “Angels and Demons” in which a secret brotherhood plots to blow up the Vatican with a time bomb whose explosive power comes from matter-antimatter annihilation. Unlike in the book, he noted, in the quantum world of the Majorana fermion there are only angels – no demons.

    The materials used for this study were produced at UCLA by a team led by postdoctoral researcher Qing Lin He and graduate student Lei Pan. Scientists from the KACST Center for Excellence in Green Nanotechnology in Saudia Arabia, UC-Davis, Florida State University, Fudan University in Shanghai and Shanghai Tech University also contributed to the experiment. Major funding came from the SHINES Center, an Energy Frontier Research Center at UC-Riverside funded by the U.S. Department of Energy Office of Science. Zhang’s work was funded by the DOE Office of Science through SIMES.

    See the full article here .

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