From Berkeley Lab: “Surprising Control over Photoelectrons from a Topological Insulator”

Berkeley Lab

Berkeley Lab scientists discover how a photon beam can flip the spin polarization of electrons emitted from an exciting new material

“Plain-looking but inherently strange crystalline materials called 3D topological insulators (TIs) are all the rage in materials science. Even at room temperature, a single chunk of TI is a good insulator in the bulk, yet behaves like a metal on its surface.

The interior bulk of a topological insulator is indeed an insulator, but electrons (spheres) move swiftly on the surface as if through a metal. They are spin-polarized, however, with their momenta (directional ribbons) and spins (arrows) locked together. Berkeley Lab researchers have discovered that the spin polarization of photoelectrons (arrowed sphere at upper right) emitted when the material is struck with high-energy photons (blue-green waves from left) is completely determined by the polarization of this incident light. (Image Chris Jozwiak, Zina Deretsky, and Berkeley Lab Creative Services Office)

Researchers find TIs exciting partly because the electrons that flow swiftly across their surfaces are ‘spin polarized’: the electron’s spin is locked to its momentum, perpendicular to the direction of travel. These interesting electronic states promise many uses – some exotic, like observing never-before-seen fundamental particles, but many practical, including building more versatile and efficient high-tech gadgets, or, further into the future, platforms for quantum computing.

A team of researchers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley has just widened the vista of possibilities with an unexpected discovery about TIs: when hit with a laser beam, the spin polarization of the electrons they emit (in a process called photoemission) can be completely controlled in three dimensions, simply by tuning the polarization of the incident light.

‘The first time I saw this it was a shock; it was such a large effect and was counter to what most researchers had assumed about photoemission from topological insulators, or any other material,’ says Chris Jozwiak of Berkeley Lab’s Advanced Light Source (ALS), who worked on the experiment. ‘Being able to control the interaction of polarized light and photoelectron spin opens a playground of possibilities.’”

See the full article here.

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From Berkeley Lab: “Searching for the Solar System’s Chemical Recipe”

Berkeley Lab

Berkeley Lab’s Chemical Dynamics Beamline points to why isotope ratios in interplanetary dust and meteorites differ from Earth’s

February 20, 2013
Paul Preuss

“By studying the origins of different isotope ratios among the elements that make up today’s smorgasbord of planets, moons, comets, asteroids, and interplanetary ice and dust, Mark Thiemens and his colleagues hope to learn how our solar system evolved. Thiemens, Dean of the Division of Physical Sciences at the University of California, San Diego, has worked on this problem for over three decades.

The protosun evolved in a hot nebula of infalling gas and dust that formed an accretion disk (green) of surrounding matter. Visible and ultraviolet light poured from the sun, irradiating abundant clouds of carbon monoxide, hydrogen sulfide, and other chemicals. Temperatures near the sun were hot enough to melt silicates and other minerals, forming the chondrules found in early meteoroids (dashed black circles). Beyond the “snowline” (dashed white curves), water, methane, and other compounds condensed to ice. Numerous chemical reactions contributed to the isotopic ratios seen in relics of the early solar system today.

In recent years his team has found the Chemical Dynamics Beamline of the Advanced Light Source (ALS) at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) to be an invaluable tool for examining how photochemistry determines the basic ingredients in the solar system recipe.

‘Mark and his colleagues Subrata Chakraborty and Teresa Jackson wanted to know if photochemistry could explain some of the differences in isotope ratios between Earth and what’s found in meteorites and interplanetary dust particles,’ says Musahid (Musa) Ahmed of Berkeley Lab’s Chemical Sciences Division, a scientist at the Chemical Dynamics Beamline who works with the UC San Diego team. ‘They needed a source of ultraviolet light powerful enough to dissociate gas molecules like carbon monoxide, hydrogen sulfide, and nitrogen. That’s us: our beamline basically provides information about gas-phase photodynamics.’”

At this point, I direct you to the full article. There is a lot going on here.

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From Berkeley Lab: “Searching for the Solar System’s Chemical Recipe”

Berkeley Lab

Berkeley Lab’s Chemical Dynamics Beamline points to why isotope ratios in interplanetary dust and meteorites differ from Earth’s

February 20, 2013
Paul Preuss

The protosun evolved in a hot nebula of infalling gas and dust that formed an accretion disk (green) of surrounding matter. Visible and ultraviolet light poured from the sun, irradiating abundant clouds of carbon monoxide, hydrogen sulfide, and other chemicals. Temperatures near the sun were hot enough to melt silicates and other minerals, forming the chondrules found in early meteoroids (dashed black circles). Beyond the “snowline” (dashed white curves), water, methane, and other compounds condensed to ice. Numerous chemical reactions contributed to the isotopic ratios seen in relics of the early solar system today. No image credit.

“By studying the origins of different isotope ratios among the elements that make up today’s smorgasbord of planets, moons, comets, asteroids, and interplanetary ice and dust, Mark Thiemens and his colleagues hope to learn how our solar system evolved. Thiemens, Dean of the Division of Physical Sciences at the University of California, San Diego, has worked on this problem for over three decades.

In recent years his team has found the Chemical Dynamics Beamline of the Advanced Light Source (ALS) at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) to be an invaluable tool for examining how photochemistry determines the basic ingredients in the solar system recipe.

‘Mark and his colleagues Subrata Chakraborty and Teresa Jackson wanted to know if photochemistry could explain some of the differences in isotope ratios between Earth and what’s found in meteorites and interplanetary dust particles,’ says Musahid (Musa) Ahmed of Berkeley Lab’s Chemical Sciences Division, a scientist at the Chemical Dynamics Beamline who works with the UC San Diego team. ‘They needed a source of ultraviolet light powerful enough to dissociate gas molecules like carbon monoxide, hydrogen sulfide, and nitrogen. That’s us: our beamline basically provides information about gas-phase photodynamics.’”

See the full article here.

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From SLAC: “Synchrotrons Explore Water’s Molecular Mysteries”

Glenn Roberts Jr.
January 31, 2013

“In experiments at SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory, scientists observed a surprisingly dense form of water that remained liquid well beyond its typical freezing point.

Illustration of the first layer of a thin film of water on a barium fluoride crystal surface, showing that the water sample exists in an unexpected, high-density liquid form, with chain-like molecular formations resembling low-density crystalline ice. (Credit: Nature Scientific Reports)

Researchers applied a superthin coating of water – no deeper than a few molecules – to the surface of a barium fluoride crystal.

This surface was expected to stimulate ice formation, but even when chilled to a temperature of about 6.5 degrees Fahrenheit – well below water’s normal freezing point – the water remained liquid.

Further, the molecular structure of the water on the crystal surface unexpectedly transformed to a high-density form in a broad temperature range, mimicking the density water achieves when pressure is applied.

The research, published Jan. 15 in Nature Scientific Reports, spanned more than three years and included experiments at SLAC’s Stanford Synchrotron Radiation Lightsource and Berkeley Lab’s Advanced Light Source synchrotrons, as well as computer simulations by collaborators in Sweden.

The work represents a milestone in understanding some of the many exotic properties water exhibits under a range of conditions, said Anders Nilsson, one of the lead authors. He is deputy director of the SUNCAT Center for Interface Science and Catalysis, a Stanford/SLAC institute, and a professor of photon science at SLAC.

Understanding the effect that certain materials have on water at the molecular scale may help scientists design materials that ‘can steer the water structure and properties,’ he said.

‘This can lead to the design of new membranes for water purification,’ Nilsson said. ‘Access to clean water will be the next crisis in the world after energy, and maybe even become more challenging.”

See the full article here.

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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From Berkeley Lab: “New Path to More Efficient Organic Solar Cells Uncovered at Berkeley Lab’s Advanced Light Source”

Berkeley Lab

January 07, 2013
Lynn Yarris

“Why are efficient and affordable solar cells so highly coveted? Volume. The amount of solar energy lighting up Earth’s land mass every year is nearly 3,000 times the total amount of annual human energy use. But to compete with energy from fossil fuels, photovoltaic devices must convert sunlight to electricity with a certain measure of efficiency. For polymer-based organic photovoltaic cells, which are far less expensive to manufacture than silicon-based solar cells, scientists have long believed that the key to high efficiencies rests in the purity of the polymer/organic cell’s two domains – acceptor and donor. Now, however, an alternate and possibly easier route forward has been shown.

Working at Berkeley Lab’s Advanced Light Source (ALS), a premier source of X-ray and ultraviolet light beams for research, an international team of scientists found that for highly efficient polymer/organic photovoltaic cells, size matters.

Berkeley ALS

‘We’ve shown that impure domains if made sufficiently small can also lead to improved performances in polymer-based organic photovoltaic cells,’ says Harald Ade, [a longtime user of the ALS] a physicist at North Carolina State University, who led this research. ‘There seems to be a happy medium, a sweet-spot of sorts, between purity and domain size that should be much easier to achieve than ultra-high purity.’”

See the full article here.

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From Berkeley Lab: “Nanocrystals Not Small Enough to Avoid Defects”

Berkeley Lab

Berkeley Lab Scientists at Advanced Light Source Show Dislocations Can Be Induced by Pressure in Ultrafine Nanocrystals

Interior of the ALS at Berkeley Lab

December 13, 2012
Lynn Yarris

“Nanocrystals as protective coatings for advanced gas turbine and jet engines are receiving a lot of attention for their many advantageous mechanical properties, including their resistance to stress. However, contrary to computer simulations, the tiny size of nanocrystals apparently does not safeguard them from defects.

Stress-induced deformation of nanocrystalline nickel reflects the dislocation activity observed by researchers at Berkeley Lab’s Advanced Light Source using a radial diamond-anvil-cell X-ray diffraction experimental station. (Image courtesy of NDT Education Resource Center)

A radial diamond-anvil-cell allows for in situ X-ray diffraction experiments at superbend beamline 12.2.2 of Berkeley Lab’s Advanced Light Source. (Photo by Roy Kaltschmidt)

In a study by researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab)and collaborators from multiple institutions, nanocrystals of nickel subjected to high pressure continued to suffer dislocation-mediated plastic deformation even when the crystals were only three nanometers in size. These experimental findings, which were carried out at Berkeley Lab’s Advanced Light Source (ALS), a premier source of X-rays and ultraviolet light for scientific research, show that dislocations can form in the finest of nanocrystals when stress is applied.

‘We cannot ignore or underestimate the role of dislocations – defects or irregularities – in fine nanocrystals as external stress can change the entire picture,’ says Bin Chen, a materials scientist with the ALS Experimental Systems Group who led this research. ‘Our results demonstrate that dislocation-mediated deformation persists to smaller crystal sizes than anticipated, primarily because computer models have not given enough consideration to the effects of external stress and grain boundaries.’”

See the full article here.

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From Berkeley Lab: “New Phenomenon in Nanodisk Magnetic Vortices”

Berkeley Lab

August 07, 2012
Lynn Yarris

“The phenomenon in ferromagnetic nanodisks of magnetic vortices – hurricanes of magnetism only a few atoms across – has generated intense interest in the high-tech community because of the potential application of these vortices in non-volatile Random Access Memory (RAM) data storage systems. New findings from scientists at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) indicate that the road to magnetic vortex RAM might be more difficult to navigate than previously supposed, but there might be unexpected rewards as well.

Mi-Young Im and Peter Fischer of Berkeley Lab’s Center for X-Ray Optics led a study at the Advanced Light Source in which it was discovered that the formation of magnetic vortices in ferromagnetic nanodisks is an asymmetric phenomenon. (Photo by Roy Kaltschmidt)

In an experiment made possible by the unique X-ray beams at Berkeley Lab’s Advanced Light Source (ALS), a team of researchers led by Peter Fischer and Mi-Young Im of the Center for X-Ray Optics (CXRO), in collaboration with scientists in Japan, discovered that contrary to what was previously believed, the formation of magnetic vortices in ferromagnetic nanodisks is an asymmetric phenomenon. It is possible that this breaking of symmetry would lead to failure in a data storage device during its initialization process.

MTXM images of in-plane (a) and out-of-plane (b) magnetic components in an array of permalloy nanodisks. In-plane magnetic rotation is shown by white arrow (a). Core polarization is marked by black (up) and white (down) spots. Image (c) shows the complete vortex configuration of each nanodisk in the array. (Images courtesy of Im and Fischer)

See the full article here.

Can’t pass up this beautiful building.

Berkeley Lab’s Advanced Light Source is a DOE national user facility that features amongst its 43 beamlines a full-field magnetic transmission soft X-ray microscope with spatial resolution down to 20 nanometers. (Photo by Roy Kaltschmidt)

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

From Berkeley Lab Advanced Light Source: “Borrowing from Nature to Produce Highly Structured Biomimetic Materials”

Berkeley Lab

Advanced Light Source

Wednesday, 27 June 2012

“Natural biological tissues are often hierarchically structured, and these structures appear to correlate strongly with tissue properties and functionalities. Finding out how a tissue self-assembles from cellular proteins has captured the interest of many biologists and material scientists who are interested in borrowing from nature’s bag of tricks to synthesize artificial materials with desired properties. A team of Berkeley Lab and University of California, Berkeley, scientists has recently discovered a method for controlling the assembly of such complex structures covering a large area from identical helical building blocks, in this case a rod-shaped virus, an accomplishment that could accelerate the development of diverse functional materials.

Illustration revealing how the arrangement of molecular building blocks yields novel functional materials with unique properties, both in nature and in the laboratory. Courtesy of Z. Deretsky, National Science Foundation.

Schematic diagram of the phage-based self-templating process. Left: The phage structure covered by about 2,700 alpha-helical major coat protein subunits having five-fold helical symmetry and a two-fold screw rotation axis (red and green arrows). Right: The self-templating assembly of phage particles. The morphology is controlled by competing interfacial forces at the meniscus where liquid-crystal phase transitions occur. The polarized optical microscopy image shows iridescent colors originating from liquid-crystal phase formation at the air–liquid–solid interface.

A self-templated helical supramolecular structure. Top center: AFM image of a left-handed smectic helicoidal nanofilament structure, which is composed of 1-µm bundles (left), and proposed model (right) of the nanofilament. The full structure consists of both left- and right-handed filaments. Bottom center: Grazing-incidence small-angle x-ray scattering measurement perpendicular to the pulling direction in a film with pseudo-hexagonally packed phage structures.

See the full article here.

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

From Berkeley Lab: “Beyond the High-Speed Hard Drive: Topological Insulators Open a Path to Room-Temperature Spintronics”

Berkeley Lab

Berkeley Lab researchers and their colleagues demonstrate unique new materials for innovative electronic and magnetic applications

May 14, 2012
Paul Preuss

“Strange new materials experimentally identified just a few years ago are now driving research in condensed-matter physics around the world. First theorized and then discovered by researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and their colleagues in other institutions, these “strong 3-D topological insulators” – TIs for short – are seemingly mundane semiconductors with startling properties. For starters, picture a good insulator on the inside that’s a good conductor on its surface – something like a copper-coated bowling ball.

Electrons on the surface of a topological insulator can flow with little resistance. Their spin and direction are intimately related; the direction of the electron determines its spin and in turn is determined by it. No image credit.

‘One way that electrons lose mobility is by scattering on phonons,’ says Alexis Fedorov, staff scientist for beamline 12.0.1 of Berkeley Lab’s Advanced Light Source (ALS). Phonons are the quantized vibrational energy of crystalline materials, treated mathematically as particles. ‘Our recent work on a particularly promising topological insulator shows that its surface electrons hardly couple with phonons at all. So there’s no impediment to developing this TI for spintronics and other applications.’”

See the full exciting article here.
A US Department of Energy National Laboratory Operated by the University of California

From Berkeley Lab: “A Surprising New Kind of Proton Transfer”

Berkeley Lab

Paul Preuss
March 18, 2012

“When a proton – the bare nucleus of a hydrogen atom – transfers from one molecule to another, or moves within a molecule, the result is a hydrogen bond, in which the proton and another atom like nitrogen or oxygen share electrons. Conventional wisdom has it that proton transfers can only happen using hydrogen bonds as conduits, proton wires of hydrogen-bonded networks that can connect and reconnect to alter molecular properties.

Hydrogen bonds are found everywhere in chemistry and biology and are critical in DNA and RNA, where they bond the base pairs that encode genes and map protein structures. Recently a team of researchers using the Advanced Light Source (ALS) at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) discovered to their surprise that in special cases protons can find ways to transfer even when hydrogen bonds are blocked. The team’s results appear in Nature Chemistry.”

Hydrogen bonds are ubiquitous but nowhere more important than in the structure of DNA and RNA, where they join the ‘stair-step’ base pairs across the double strand. It has long been thought that protons transfer in molecules only by means of such hydrogen bonds. No image credit

See the full article here.
A U.S. Department of Energy National Laboratory Operated by the University of California