A First For Direct-Drive Fusion

Scientists at the University of Rochester have taken a significant step forward in laser fusion research.

Experiments using the OMEGA laser at the University’s Laboratory of Laser Energetics (LLE) have created the conditions capable of producing a fusion yield that’s five times higher than the current record laser-fusion energy yield, as long as the relative conditions produced at LLE are reproduced and scaled up at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California.

The findings are the result of multiple experiments conducted by LLE scientists Sean Regan, Valeri Goncharov, and collaborators, whose paper was published in Physical Review Letters. Arijit Bose, a doctoral student in physics at Rochester working with Riccardo Betti, a professor of engineering and physics, interpreted those findings in a paper published as Rapid Communications in the journal Physical Review E (R).

Bose reports that the conditions at LLE would produce over 100 kilojoules (kJ) of fusion energy if replicated on the NIF. While that may seem like a tiny flicker in the world’s ever-expanding demand for energy, the new work represents an important advance in a long-standing national research initiative to develop fusion as an energy source. The 100 kJ is the energy output of a 100-watt light for about 20 minutes, but in a fusion experiment at NIF, that energy would be released in less than a billionth of a second and enough to bring the fuel a step closer to the ignition conditions.

“We have compressed thermonuclear fuel to about half the pressure required to ignite it. This is the result of a team effort involving many LLE scientists and engineers,” said Regan, the leader of the LLE experimental group.

If ignited, thermonuclear fuel would unleash copious amounts of fusion energy, much greater than the input energy to the fuel.

“In laser fusion, an ignited target is like a miniature star of about a 10th of a millimeter, which produces the energy equivalent of a few gallons of gasoline over a fraction of a billionth of a second. We are not there yet, but we are making progress” said Betti, the Robert L. McCrory Professor at the Laboratory for Laser Energetics.

In terms of proximity to the conditions required to ignite the fuel, the two recent LLE papers report that OMEGA experiments match the current NIF record when extrapolated to NIF energies. Igniting a target is the main goal of the laser fusion effort in the United States.

As part of their work, researchers carefully targeted the LLE’s 60 laser beams to strike a millimeter-sized pellet of fuel–an approach known as the direct-drive method of inertial confinement fusion (ICF).

The results indicate that the direct-drive approach used by LLE, home to the most prolific laser in the world (in terms of number of experiments, publications, and diversity of users) is a promising path to fusion and a viable alternative over other methods, including that used at NIF. There, researchers are working to achieve fusion by using 192 laser beams in an approach known as indirect-drive, in which the laser light is first converted into x-rays in a gold enclosure called a hohlraum. While not yet achieving ignition, scientists at LLNL and colleagues in the ICF Community have made significant progress in understanding the physics and developing innovative approaches to indirect drive fusion.

“We’ve shown that the direct-drive method, is on par with other work being done in advancing nuclear fusion research,” said Bose.

“Arijit’s work is very thorough and convincing. While much work remains to be done, this result shows significant progress in the direct-drive approach, “says Betti.

Research at both LLE and NIF is based on inertial confinement, in which nuclear fusion reactions take place by heating and compressing–or imploding–a target containing a fuel made of deuterium and tritium (DT). The objective is to have the atoms collide with enough energy that the nuclei fuse to form a helium nuclei and a free neutron, releasing significant energy in the process.

In both methods being explored at LLE and NIF, a major challenge is creating a self-sustaining burn that would ignite all the fuel in the target shells. As a result, it’s important that enough heat is created when helium nuclei are initially formed to keep the process going. The helium nuclei are called alpha particles, and the heat produced is referred to as alpha heating.

E. Michael Campbell, deputy director of LLE and part of the research team, said the results were made possible because of a number of improvements in the direct-method approach.

One involved the aiming of the 60 laser beams, which now strike the target more uniformly.

“It’s like squeezing a balloon with your hands; there are always parts that pop out where your hands aren’t,” said Campbell. “If it were possible to squeeze a balloon from every spot on the surface, there would be a great deal more pressure inside. And that’s what happens when the lasers strike a target more symmetrically.”

“If we can improve the uniformity of the way we compress our targets, we will likely get very close to the conditions that would extrapolate to ignition on NIF. This is what we will be focusing on in the near future” says Goncharov, the new director of the LLE theory division.

Two other enhancements were made at LLE: the quality of the target shell was improved to make it more easily compressed, and the diagnostics for measuring what’s taking place within the shell have gotten better. Researchers are now able to capture x-ray images of the target’s implosion with frame times of 40 trillionths of a second, giving them information on how to more precisely adjust the lasers and understand the physics.

“What we’ve done is show the advantages of a direct-drive laser in the nuclear fusion process,” said Campbell. “And that should lead to additional research opportunities, as well as continued progress in the field.”

Bose says the next step is to develop theoretical estimates of what is taking place in the target shell as it’s being hit by the laser. That information will help scientists make further enhancements.

Electron Beam Microscope Directly Writes Nanoscale Features In Liquid With Metal Ink

Scientists at the Department of Energy’s Oak Ridge National Laboratory are the first to harness a scanning transmission electron microscope (STEM) to directly write tiny patterns in metallic “ink,” forming features in liquid that are finer than half the width of a human hair.

The automated process is controlled by weaving a STEM instrument’s electron beam through a liquid-filled cell to spur deposition of metal onto a silicon microchip. The patterns created are “nanoscale,” or on the size scale of atoms or molecules.

Usually fabrication of nanoscale patterns requires lithography, which employs masks to prevent material from accumulating on protected areas. ORNL’s new direct-write technology is like lithography without the mask.

Details of this unique capability are published online in Nanoscale, a journal of the Royal Society of Chemistry, and researchers are applying for a patent. The technique may provide a new way to tailor devices for electronics and other applications.

“We can now deposit high-purity metals at specific sites to build structures, with tailored material properties for a specific application,” said lead author Raymond Unocic of the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility at ORNL. “We can customize architectures and chemistries. We’re only limited by systems that are dissolvable in the liquid and can undergo chemical reactions.”

The experimenters used grayscale images to create nanoscale templates. Then they beamed electrons into a cell filled with a solution containing palladium chloride. Pure palladium separated out and deposited wherever the electron beam passed.

Liquid environments are a must for chemistry. Researchers first needed a way to encapsulate the liquid so the extreme dryness of the vacuum inside the microscope would not evaporate the liquid. The researchers started with a cell made of microchips with a silicon nitride membrane to serve as a window through which the electron beam could pass.

Then they needed to elicit a new capability from a STEM instrument. “It’s one thing to utilize a microscope for imaging and spectroscopy. It’s another to take control of that microscope to perform controlled and site-specific nanoscale chemical reactions,” Unocic said. “With other techniques for electron-beam lithography, there are ways to interface that microscope where you can control the beam. But this isn’t the way that aberration-corrected scanning transmission electron microscopes are set up.”

Enter Stephen Jesse, leader of CNMS’s Directed Nanoscale Transformations theme. This group looks at tools that scientists use to see and understand matter and its nanoscale properties in a new light, and explores whether those tools can also transform matter one atom at a time and build structures with specified functions. “Think of what we are doing as working in nanoscale laboratories,” Jesse said. “This means being able to induce and stop reactions at will, as well as monitor them while they are happening.”

Jesse had recently developed a system that serves as an interface between a nanolithography pattern and a STEM’s scan coils, and ORNL researchers had already used it to selectively transform solids. The microscope focuses the electron beam to a fine point, which microscopists could move just by taking control of the scan coils. Unocic with Andrew Lupini, Albina Borisevich and Sergei Kalinin integrated Jesse’s scan control/nanolithography system within the microscope so that they could control the beam entering the liquid cell. David Cullen performed subsequent chemical analysis.

“This beam-induced nanolithography relies critically on controlling chemical reactions in nanoscale volumes with a beam of energetic electrons,” said Jesse. The system controls electron-beam position, speed and dose. The dose–how many electrons are being pumped into the system–governs how fast chemicals are transformed.

This nanoscale technology is similar to larger-scale activities, such as using electron beams to transform materials for 3D printing at ORNL’s Manufacturing Demonstration Facility. In that case, an electron beam melts powder so that it solidifies, layer by layer, to create an object.

“We’re essentially doing the same thing, but within a liquid,” Unocic said. “Now we can create structures from a liquid-phase precursor solution in the shape that we want and the chemistry that we want, tuning the physiochemical properties for a given application.”

Precise control of the beam position and the electron dose produces tailored architectures. Encapsulating different liquids and sequentially flowing them during patterning customizes the chemistry too.

The current resolution of metallic “pixels” the liquid ink can direct-write is 40 nanometers, or twice the width of an influenza virus. In future work, Unocic and colleagues would like to push the resolution down to approach the state of the art of conventional nanolithography, 10 nanometers. They would also like to fabricate multi-component structures.

The title of the paper is “Direct-write liquid phase transformations with a scanning transmission electron microscope.”

Recreating Our Galaxy In A Supercomputer

Astronomers have created the most detailed computer simulation to date of our Milky Way galaxy’s formation, from its inception billions of years ago as a loose assemblage of matter to its present-day state as a massive, spiral disk of stars.

The simulation solves a decades-old mystery surrounding the tiny galaxies that swarm around the outside of our much larger Milky Way. Previous simulations predicted that thousands of these satellite, or dwarf, galaxies should exist. However, only about 30 of the small galaxies have ever been observed. Astronomers have been tinkering with the simulations, trying to understand this “missing satellites” problem to no avail.

Now, with the new simulation—which used a network of thousands of computers running in parallel for 700,000 central processing unit (CPU) hours—Caltech astronomers have created a galaxy that looks like the one we live in today, with the correct, smaller number of dwarf galaxies.

“That was the aha moment, when I saw that the simulation can finally produce a population of dwarf galaxies like the ones we observe around the Milky Way,” says Andrew Wetzel, postdoctoral fellow at Caltech and Carnegie Observatories in Pasadena, and lead author of a paper about the new research, published August 20 in Astrophysical Journal Letters.

One of the main updates to the new simulation relates to how supernovae, explosions of massive stars, affect their surrounding environments. In particular, the simulation incorporated detailed formulas that describe the dramatic effects that winds from these explosions can have on star-forming material and dwarf galaxies. These winds, which reach speeds up to thousands of kilometers per second, “can blow gas and stars out of a small galaxy,” says Wetzel.

Indeed, the new simulation showed the winds can blow apart young dwarf galaxies, preventing them from reaching maturity. Previous simulations that were producing thousands of dwarf galaxies weren’t taking the full effects of supernovae into account.

“We had thought before that perhaps our understanding of dark matter was incorrect in these simulations, but these new results show we don’t have to tinker with dark matter,” says Wetzel. “When we more precisely model supernovae, we get the right answer.”

Astronomers simulate our galaxy to understand how the Milky Way, and our solar system within it, came to be. To do this, the researchers tell a computer what our universe was like in the early cosmos. They write complex codes for the basic laws of physics and describe the ingredients of the universe, including everyday matter like hydrogen gas as well as dark matter, which, while invisible, exerts gravitational tugs on other matter. The computers then go to work, playing out all the possible interactions between particles, gas, and stars over billions of years.

“In a galaxy, you have 100 billion stars, all pulling on each other, not to mention other components we don’t see like dark matter,” says Caltech’s Phil Hopkins, associate professor of theoretical astrophysics and principal scientist for the new research. “To simulate this, we give a supercomputer equations describing those interactions and then let it crank through those equations repeatedly and see what comes out at the end.”

The researchers are not done simulating our Milky Way. They plan to use even more computing time, up to 20 million CPU hours, in their next rounds. This should lead to predictions about the very faintest and smallest of dwarf galaxies yet to be discovered. Not a lot of these faint galaxies are expected to exist, but the more advanced simulations should be able to predict how many are left to find.

The study, titled “Reconciling Dwarf Galaxies with ΛCDM Cosmology: Simulating A Realistic Population of Satellites Around a Milky Way-Mass Galaxy,” was funded by Caltech, a Sloan Research Fellowship, the National Science Foundation, NASA, an Einstein Postdoctoral Fellowship, the Space Telescope Science Institute, UC San Diego, and the Simons Foundation. Other coauthors on the study are: Ji-Hoon Kim of Stanford University, Claude-André Faucher-Giguére of Northwestern University, Dušan Kereš of UC San Diego, and Eliot Quataert of UC Berkeley.

World’s Most Powerful X-Ray Takes A ‘Sledgehammer’ To Molecules

An international team of more than 20 scientists has inadvertently discovered how to create a new type of crystal using light more than ten billion times brighter than the sun.

The discovery, led by Associate Professor Brian Abbey at La Trobe in collaboration with Associate Professor Harry Quiney at the University of Melbourne, has been published in the journal Science Advances.

Their findings reverse what has been accepted thinking in crystallography for more than 100 years.

The team exposed a sample of crystals, known as Buckminsterfullerene or Buckyballs, to intense light emitted from the world’s first hard X-ray free electron laser (XFEL), based at Stanford University in the United States. The molecules have a spherical shape forming a pattern that resembles panels on a soccer ball.

Light from the XFEL is around one billion times brighter than light generated by any other X-ray equipment –even light from the Australian Synchrotron pales in comparison. Because other X-ray sources deliver their energy much slower than the XFEL, all previous observations had found that the X-rays randomly melt or destroy the crystal. Scientists had previously assumed that XFELs would do the same.

The result from the XFEL experiments on Buckyballs, however, was not at all what scientists expected. When the XFEL intensity was cranked up past a critical point, the electrons in the Buckyballs spontaneously re-arranged their positions, changing the shape of the molecules completely.

Every molecule in the crystal changed from being shaped like a soccer ball to being shaped like an AFL ball at the same time. This effect produces completely different images at the detector. It also altered the sample’s optical and physical properties.

“It was like smashing a walnut with a sledgehammer and instead of destroying it and shattering it into a million pieces, we instead created a different shape – an almond!” Assoc. Prof. Abbey said.

“We were stunned, this is the first time in the world that X-ray light has effectively created a new type of crystal phase” said Associate Professor Quiney, from the School of Physics, University of Melbourne.

“Though it only remains stable for a tiny fraction of a second, we observed that the sample’s physical, optical and chemical characteristics changed dramatically, from its original form,” he said.

“This change means that when we use XFELs for crystallography experiments we will have to change the way interpret the data. The results give the 100-year-old science of crystallography a new, exciting direction,” Assoc. Prof. Abbey said.

“Currently, crystallography is the tool used by biologists and immunologists to probe the inner workings of proteins and molecules — the machines of life. Being able to see these structures in new ways will help us to understand interactions in the human body and may open new avenues for drug development.”

The study was conducted by researchers from the ARC Centre of Excellence in Advanced Molecular Imaging, La Trobe University, the University of Melbourne, Imperial College London, the CSIRO, the Australian Synchrotron, Swinburne Institute of Technology, the University of Oxford, Brookhaven National Laboratory, the Stanford Linear Accelerator (SLAC), the BioXFEL Science and Technology Centre, Uppsala University and the Florey Institute of Neuroscience and Mental Health.

UCLA Chemists Report New Insights About Properties Of Matter At The Nanoscale

UCLA nanoscience researchers have determined that a fluid that behaves similarly to water in our day-to-day lives becomes as heavy as honey when trapped in a nanocage of a porous solid, offering new insights into how matter behaves in the nanoscale world.

“We are learning more and more about the properties of matter at the nanoscale so that we can design machines with specific functions,” said senior author Miguel García-Garibay, dean of the UCLA Division of Physical Sciences and professor of chemistry and biochemistry.

The research is published in the journal ACS Central Science.

Just how small is the nanoscale? A nanometer is less than 1/1,000 the size of a red blood cell and about 1/20,000 the diameter of a human hair. Despite years of research by scientists around the world, the extraordinarily small size of matter at the nanoscale has made it challenging to learn how motion works at this scale.

“This exciting research, supported by the National Science Foundation, represents a seminal advance in the field of molecular machines,” said Eugene Zubarev, a program director at the NSF. “It will certainly stimulate further work, both in basic research and real-life applications of molecular electronics and miniaturized devices. Miguel Garcia-Garibay is among the pioneers of this field and has a very strong record of high-impact work and ground-breaking discoveries.”

Possible uses for complex nanomachines that could be much smaller than a cell include placing a pharmaceutical in a nanocage and releasing the cargo inside a cell, to kill a cancer cell, for example; transporting molecules for medical reasons; designing molecular computers that potentially could be placed inside your body to detect disease before you are aware of any symptoms; or perhaps even to design new forms of matter.

To gain this new understanding into the behavior of matter at the nanoscale, García-Garibay’s research group designed three rotating nanomaterials known as MOFs, or metal-organic frameworks, which they call UCLA-R1, UCLA-R2 and UCLA-R3 (the “r” stands for rotor). MOFs, sometimes described as crystal sponges, have pores — openings which can store gases, or in this case, liquid.

Studying the motion of the rotors allowed the researchers to isolate the role a fluid’s viscosity plays at the nanoscale. With UCLA-R1 and UCLA-R2 the molecular rotors occupy a very small space and hinder one another’s motion. But in the case of UCLA-R3, nothing slowed down the rotors inside the nanocage except molecules of liquid.

García-Garibay’s research group measured how fast molecules rotated in the crystals. Each crystal has quadrillions of molecules rotating inside a nanocage, and the chemists know the position of each molecule.

UCLA-R3 was built with large molecular rotors that move under the influence of the viscous forces exerted by 10 molecules of liquid trapped in their nanoscale surroundings.

“It is very common when you have a group of rotating molecules that the rotors are hindered by something within the structure with which they interact — but not in UCLA-R3,” said García-Garibay, a member of the California NanoSystems Institute at UCLA. “The design of UCLA-R3 was successful. We want to be able to control the viscosity to make the rotors interact with one another; we want to understand the viscosity and the thermal energy to design molecules that display particular actions. We want to control the interactions among molecules so they can interact with one another and with external electric fields.”

García-Garibay’s research team has been working for 10 years on motion in crystals and designing molecular motors in crystals. Why is this so important?

“I can get a precise picture of the molecules in the crystals, the precise arrangement of atoms, with no uncertainty,” García-Garibay said. “This provides a large level of control, which enables us to learn the different principles governing molecular functions at the nanoscale.”

García-Garibay hopes to design crystals that take advantage of properties of light, and whose applications could include advances in communications technology, optical computing, sensing and the field of photonics, which takes advantage of the properties of light; light can have enough energy to break and make bonds in molecules.

“If we are able to convert light, which is electromagnetic energy, into motion, or convert motion into electrical energy, then we have the potential to make molecular devices much smaller,” he said. “There will be many, many possibilities for what we can do with molecular machines. We don’t yet fully understand what the potential of molecular machinery is, but there are many applications that can be developed once we develop a deep understanding of how motion takes place in solids.”

Co-authors are lead author Xing Jiang, a UCLA graduate student in García-Garibay’s laboratory, who this year completed his Ph.D.; Hai-Bao Duan, a visiting scholar from China’s Nanjing Xiao Zhuang University who spent a year conducting research in García-Garibay’s laboratory; and Saeed Khan, a UCLA crystallographer in the department of chemistry and biochemistry.

The research was funded by the National Science Foundation (grant DMR140268).

García-Garibay will continue his research on molecular motion in crystals and green chemistry during his tenure as dean.

Efficiency Plus Versatility In New Method Of Engineering Polymer Brush Patterns

Antimicrobial cutting boards. Flame-retardant carpets. Friction-resistant bearings. Engineered surfaces add value to the things we use, providing extra layers of safety, easing their operation, preserving their quality or adding utility.

At UC Santa Barbara, materials researchers are looking to greatly improve on the concept with a method of micron-scale surface chemical patterning that can not only decrease time and money spent in their manufacture, but also add versatility to their design. In a paper describing a method called “sequential stop-flow photopatterning,” UCSB materials scientists describe a new platform for functionalizing and engineering surfaces with patterned polymer brushes.

“It’s a really powerful tool you can use for many purposes,” said Christian Pester, a postdoctoral researcher in the Craig Hawker Lab at UCSB. He is the lead author of the paper, which appears in the journal Advanced Materials.

If you take a close look at some engineered surfaces, you’ll see that at the micro- and nanoscale, they aren’t flat and empty, but rather consist of infinitesimal elongated polymer molecules attached at one end to the surface. These polymer brushes imbue the surface with various properties and functions. They can, for instance, repel water, prevent bacteria from attaching, enhance drug delivery or attract other molecules. Patterning polymer brushes allows the combination of multiple functionalities.

Conventional methods of patterning polymer brushes on surfaces are often repetitive and time-consuming, Pester said. For more than one brush, the first polymer growth from an initiating “seed” must be deactivated and the synthetic process repeated after re-depositing new initiating molecules. It can take up to the better part of a day for each type of polymer brush, he added.

With sequential stop-flow photopatterning, the intermediate steps can be eliminated, Pester said.

“It’s also chemically more clean, because you’re not iteratively depositing the initiator,” he said, “which means you’re also taking away related washing and cleansing steps.”

To accomplish this feat, the substrate (with initiating molecules deposited) is enclosed in a stop-flow cell and a solution streamed in. Irradiation with light can then initiate the reaction. A separate photomask — essentially a sort of stencil — is positioned over the top of the cell, thus allowing only some light-activated growth. After the growth step, the light is turned off, the first solution is drained from the cell and a second one isflowed in to functionalize the polymers. Since neither the mask nor the substrate has been moved, only the molecules that have been exposed to light are grown and functionalized. These basic steps may be repeated with variations in the reactants, the light source or the positions of the substrate or the photomask to create polymer brush patterns in a single continuous process.

“We can also create chemical and height gradients on the nanoscale,” Pester said, features that are only indirectly accessible with conventional methods.

The technology opens the door to increased versatility in the development of polymer brushes with an eye toward industrial applications. Pester credits the collaborative nature of UCSB research for this scientific development, which is dedicated to the late Edward J. Kramer, materials professor and founder of the campus’s Materials Research Laboratory. “I think what is really cool about this project and I think where UCSB shines is in collaboration,” said Pester.

Research on this paper was conducted also by Kaila Mattson, Benjaporn Narupai, and Emre Discekici from UCSB’s departments of chemistry and biochemistry and of materials. David Bothman from the Department of Mechanical Engineering and Kenneth Lee from the Department of Physics also contributed research, as did Daniel Klinger at the Institut Für Pharmazie, Freie Universität Berlin.

Researchers Reveal That Magnetic ‘Rust’ Performs As Gold At The Nanoscale

Researchers from the University of Georgia are giving new meaning to the phrase “turning rust into gold”—and making the use of gold in research settings and industrial applications far more affordable.

The research is akin to a type of modern-day alchemy, said Simona Hunyadi Murph, adjunct professor in the UGA Franklin College of Arts and Sciences department of physics and astronomy. Researchers combine small amounts of gold nanoparticles with magnetic rust nanoparticles to create a hybrid nanostructure that retains both the properties of gold and rust.

“Medieval alchemists tried to create gold from other metals,” she said. “That’s kind of what we did with our research. It’s not real alchemy, in the medieval sense, but it is a sort of 21st century version.”

Gold has long been a valuable resource for industry, medicine, dentistry, computers, electronics and aerospace, among others, due to unique physical and chemical properties that make it inert and resistant to oxidation. But because of its high cost and limited supply, large scale projects using gold can be prohibitive. At the nanoscale, however, using a very small amount of gold is far more affordable.

In the new study published this summer in the Journal of Physical Chemistry C, the researchers used solution chemistry to reduce gold ions into a metallic gold structure using sodium citrate. In this process, if other ingredients-rust in this case-are present in the reaction pot during the transformation process, the metallic gold structures nucleate and grow on these “ingredients,” otherwise known as supports.

“We are really excited to share our new discoveries. When researchers are looking at gold as a potential material for research, we talk about how expensive gold is. For the first time ever, we’ve been able to create a new class of cheaper, highly efficient, nontoxic, magnetically reusable hybrid nanomaterials that contain a far more abundant material-rust-than the typical noble metal gold,” said Murph, who is also a principal scientist in the National Security Directorate at the Savannah River National Laboratory in Aiken, South Carolina.

When materials are broken down in size to reach nanometer scale dimensions-1-100 nanometers, which is approximately 100,000 times smaller than the diameter of human hair-these substances can take on new properties. For example, bulk gold does not display catalytic properties; however, at the nanoscale, gold is an efficient catalyst, accelerating chemical change for many reactions including oxidation, hydrogen production or reduction of aromatic nitro compounds.

Gold nanoparticles of different sizes and shapes display different colors when impinged by light because they absorb and scatter light at specific wavelengths, known as plasmonic resonances. These plasmonic resonances are of particular interest for biological applications. If someone shines light on the gold nanoparticles, the absorbed light can be converted to heat in the surrounding media, and if bacteria or cancerous cells are in the vicinity of such gold nanoparticles, they can be destroyed by using light of appropriate wavelength. This phenomenon is known as photothermal therapy.

By replacing some of the nano-gold with magnetic nano-rust, researchers show that the hybrid gold and rust nanostructures are able to photothermally heat the surrounding media as efficiently as pure gold nanoparticles, even with a significantly smaller concentration of gold.

“In a way, we’ve done a little better than alchemy,” said George Larsen, co-investigator and postdoctoral researcher in the Group for Innovation and Advancements in Nano-Technology Sciences at the Savannah River National Laboratory, “because these new hybrid nanoparticles not only behave better than gold in some cases, but also have magnetic functionality.”

Murph and her team looked at three different shapes of hybrid nanoparticles in this research-spheres, rings and tubes.

“A differently shaped nanoparticle means that the atoms are arranged differently-into cubes, hexagons or triangles, for example,” she said. “A different atom arrangement means different packing densities, spacing between atoms, defects, surface area and surface energies. Different shapes lead to an increased atom area that is exposed to catalyze a chemical reaction. Scientifically speaking, different shape means different crystallographic facets and surface energy that could lead to higher catalytic activity and different catalytic products.

“The results of our research showed that the ring- and tube-shaped hybrid nanoparticles proved to be better catalytic materials than the sphere-shaped nanoparticles because of the way the atoms are arranged in the structure at this nanoscale. More importantly, the hybrid nanoparticles of gold and rust are better catalysts than gold nanoparticles alone, even with a significantly smaller amount of gold.

When these different shaped hybrid nanoparticles were exposed to light of specific wavelength, the spheres heated the solution up to slightly higher temperatures than the ring- or tube-shaped nanoparticles.

“This could have a variety of biological applications such as tracking, drug delivery or imaging inside the body,” Murph said. “If you feed these gold nanoparticles to bacteria and shine the light on them, you could destroy these by just using light.”

The hybrid structures could also be used for new application, such as sensing, hyperthermia treatment, environmental cleaning and protection medical imaging applications including magnetic resonance imaging contrast agents, product detection and manipulation.

The research study, “Multifunctional Hybrid Fe2O3-Au Nanoparticles for Efficient Plasmonic Heating,” is available at http://www.jove.com/video/53598/multifunctional-hybrid-fe2o3-au-nanoparticles-for-efficient-plasmonic.

The study was supported by Department of Energy Laboratory Directed Research & Development Strategic Initiative Program of the Savannah River National Laboratory.

Additional co-investigators on this study were Robert Lascola and Will Farr of the Savannah River National Laboratory.

For First Time, Researchers See Individual Atoms Keep Away From Each Other Or Bunch Up As Pairs

If you bottle up a gas and try to image its atoms using today’s most powerful microscopes, you will see little more than a shadowy blur. Atoms zip around at lightning speeds and are difficult to pin down at ambient temperatures.

If, however, these atoms are plunged to ultracold temperatures, they slow to a crawl, and scientists can start to study how they can form exotic states of matter, such as superfluids, superconductors, and quantum magnets.

Physicists at MIT have now cooled a gas of potassium atoms to several nanokelvins — just a hair above absolute zero — and trapped the atoms within a two-dimensional sheet of an optical lattice created by crisscrossing lasers. Using a high-resolution microscope, the researchers took images of the cooled atoms residing in the lattice.

By looking at correlations between the atoms’ positions in hundreds of such images, the team observed individual atoms interacting in some rather peculiar ways, based on their position in the lattice. Some atoms exhibited “antisocial” behavior and kept away from each other, while some bunched together with alternating magnetic orientations. Others appeared to piggyback on each other, creating pairs of atoms next to empty spaces, or holes.

The team believes that these spatial correlations may shed light on the origins of superconducting behavior. Superconductors are remarkable materials in which electrons pair up and travel without friction, meaning that no energy is lost in the journey. If superconductors can be designed to exist at room temperature, they could initiate an entirely new, incredibly efficient era for anything that relies on electrical power.

Martin Zwierlein, professor of physics and principal investigator at MIT’s NSF Center for Ultracold Atoms and at its Research Laboratory of Electronics, says his team’s results and experimental setup can help scientists identify ideal conditions for inducing superconductivity.

“Learning from this atomic model, we can understand what’s really going on in these superconductors, and what one should do to make higher-temperature superconductors, approaching hopefully room temperature,” Zwierlein says.

Zwierlein and his colleagues’ results appear in the Sept. 16 issue of the journal Science. Co-authors include experimentalists from the MIT-Harvard Center for Ultracold Atoms, MIT’s Research Laboratory of Electronics, and two theory groups from San Jose State University, Ohio State University, the University of Rio de Janeiro, and Penn State University.

“Atoms as stand-ins for electrons”

Today, it is impossible to model the behavior of high‐temperature superconductors, even using the most powerful computers in the world, as the interactions between electrons are very strong. Zwierlein and his team sought instead to design a “quantum simulator,” using atoms in a gas as stand-ins for electrons in a superconducting solid.

The group based its rationale on several historical lines of reasoning: First, in 1925 Austrian physicist Wolfgang Pauli formulated what is now called the Pauli exclusion principle, which states that no two electrons may occupy the same quantum state — such as spin, or position — at the same time. Pauli also postulated that electrons maintain a certain sphere of personal space, known as the “Pauli hole.”

His theory turned out to explain the periodic table of elements: Different configurations of electrons give rise to specific elements, making carbon atoms, for instance, distinct from hydrogen atoms.

The Italian physicist Enrico Fermi soon realized that this same principle could be applied not just to electrons, but also to atoms in a gas: The extent to which atoms like to keep to themselves can define the properties, such as compressibility, of a gas.

“He also realized these gases at low temperatures would behave in peculiar ways,” Zwierlein says.

British physicist John Hubbard then incorporated Pauli’s principle in a theory that is now known as the Fermi-Hubbard model, which is the simplest model of interacting atoms, hopping across a lattice. Today, the model is thought to explain the basis for superconductivity. And while theorists have been able to use the model to calculate the behavior of superconducting electrons, they have only been able to do so in situations where the electrons interact weakly with each other.

“That’s a big reason why we don’t understand high-temperature superconductors, where the electrons are very strongly interacting,” Zwierlein says. “There’s no classical computer in the world that can calculate what will happen at very low temperatures to interacting [electrons]. Their spatial correlations have also never been observed in situ, because no one has a microscope to look at every single electron.”

Carving out personal space

Zwierlein’s team sought to design an experiment to realize the Fermi-Hubbard model with atoms, in hopes of seeing behavior of ultracold atoms analogous to that of electrons in high-temperature superconductors.

The group had previously designed an experimental protocol to first cool a gas of atoms to near absolute zero, then trap them in a two-dimensional plane of a laser-generated lattice. At such ultracold temperatures, the atoms slowed down enough for researchers to capture them in images for the first time, as they interacted across the lattice.

At the edges of the lattice, where the gas was more dilute, the researchers observed atoms forming Pauli holes, maintaining a certain amount of personal space within the lattice.

“They carve out a little space for themselves where it’s very unlikely to find a second guy inside that space,” Zwierlein says.

Where the gas was more compressed, the team observed something unexpected: Atoms were more amenable to having close neighbors, and were in fact very tightly bunched. These atoms exhibited alternating magnetic orientations.

“These are beautiful, antiferromagnetic correlations, with a checkerboard pattern — up, down, up, down,” Zwierlein describes.

At the same time, these atoms were found to often hop on top of one another, creating a pair of atoms next to an empty lattice square. This, Zwierlein says, is reminiscent of a mechanism proposed for high-temperature superconductivity, in which electron pairs resonating between adjacent lattice sites can zip through the material without friction if there is just the right amount of empty space to let them through.

Ultimately, he says the team’s experiments in gases can help scientists identify ideal conditions for superconductivity to arise in solids.

Zwierlein explains: “For us, these effects occur at nanokelvin because we are working with dilute atomic gases. If you have a dense piece of matter, these same effects may well happen at room temperature.”

Currently, the team has been able to achieve ultracold temperatures in gases that are equivalent to hundreds of kelvins in solids. To induce superconductivity, Zwierlein says the group will have to cool their gases by another factor of five or so.

“We haven’t played all of our tricks yet, so we think we can get colder,” he says.

This research was supported in part by the National Science Foundation, the Air Force Office of Scientific Research, the Army Research Office, and the David and Lucile Packard Foundation.

Closing In On High-Temperature Superconductivity

The quest to know the mysterious recipe for high-temperature superconductivity, which could enable revolutionary advances in technologies that make or use electricity, just took a big leap forward thanks to new research by an international team of experimental and theoretical physicists.

The research paper appears in the journal Science on Sept. 16, 2016. The research is focused on revealing the mysterious ingredients required for high-temperature superconductivity — the ability of a material’s electrons to pair up and travel without friction at relatively high temperatures, enabling them to lose no energy — to be super efficient — while conducting electricity.

The research team’s achievements are an important step in recent efforts to improve today’s superconducting materials, which have superconducting powers only if they are cooled below a critical temperature, hundreds of degrees below the freezing point of water — temperatures at which helium is a liquid — making them impractical for use in most electronic devices.

“We want to understand exactly which ingredients are necessary for high-temperature superconductivity, a beautiful quantum phenomenon with potentially important uses,” said Marcos Rigol, professor of physics at Penn State University and a theorist on the research team led by Martin Zwierlein, professor of physics and principal investigator at the NSF Center for Ultracold Atoms and the Research Laboratory of Electronics at the Massachusetts Institute of Technology (MIT).

For the first time, experimenters on the team have made hundreds of observations of individual potassium atoms, cooled to just slightly above absolute zero, trapped by lasers in a two-dimensional grid, and interacting with each other in intriguing ways that could help to reveal the behaviors of superconducting electrons. The team’s scientists suspect that they have observed one of the important dynamics that contribute to producing high-temperature superconductivity; that is, that electrons start forming pairs that “bunch” with empty spaces in the lattice.

An important contribution of the theorists on the team is their demonstration that the mathematical model developed to understand real materials (the so-called Hubbard model) could reproduce the behaviors of the atoms in the team’s 2-D experiments within a certain temperature range.

“If we can discover all the essential ingredients for superconductivity, we will have the opportunity to design recipes — theoretical models — for making high-temperature superconducting materials that can have a wide range of practical and innovative uses,” Rigol said.

Zwierlein led the team in building the experimental setup to help identify the ideal conditions for inducing superconductivity. This “quantum simulator” experiment uses atoms in a 2-D gas as stand-ins for electrons in a superconducting solid in order “to understand what’s really going on in these superconductors, and what one should do to make higher-temperature superconductors, approaching hopefully room temperature,” Zwierlein said.

Because of strong interactions, which are thought to be essential for high-temperature superconductivity to occur, not even the most powerful computers in the world have been able to solve the Hubbard model at the temperatures at which electrons are expected to become superconducting. A challenge for physicists, then, is to come up with computational techniques that can solve this model at the lowest possible temperatures in the current supercomputers. Rigol and collaborators developed one such technique, which was able to describe the experimental results.

“Our theoretical results precisely describe how the atoms in our team’s 2-D experiments actually behaved within the accessible temperature range,” Rigol said. “If future experiments are able to demonstrate at lower temperatures that the atoms in the experimental quantum simulator become superconducting — at temperatures at which our equations are just too difficult to solve — then we will know for sure that our theoretical model of high-temperature superconductivity is a good one.” The approach is a bit like one used in the field of astrophysics, where the experimental detection of gravitational waves recently served as a test and a validation of Einstein’s theory of general relativity.

The team’s results are important because, if superconductivity is observed at lower experimental temperatures, “we will know for sure that strong repulsive interactions between the electrons can produce high-temperature superconductivity,” Rigol said.

“Achieving this understanding could have a profound impact in technology, as well, because knowing the features of a material that are necessary for producing high-temperature superconductivity could lead to the engineering of more advanced superconducting materials.”

In addition to Rigol at Penn State and Zwierlein at MIT, the research team includes Lawrence W. Cheuk, Matthew A. Nichols, Katherine R. Lawrence, Melih Okan, and Hao Zhang at the MIT-Harvard Center for Ultracold Atoms; Ehsan Khatami (a former postdoctoral researcher in Rigol’s group) at San José State University; Nandini Trivedi at Ohio State University; and Thereza Paiva at the Universidade Federal do Rio de Janiero.

This research was supported, in part, by the National Science Foundation, the Air Force Office of Scientific Research, the Army Research Office, and the David and Lucile Packard Foundation.

‘Schroedinger’s Cat’ Molecules Give Rise To Exquisitely Detailed Movies

One of the most famous mind-twisters of the quantum world is the thought experiment known as “Schroedinger’s Cat,” in which a cat placed in a box and potentially exposed to poison is simultaneously dead and alive until someone opens the box and peeks inside.

Scientists have known for a long time that an atom or molecule can also be in two different states at once. Now researchers at the Stanford PULSE Institute and the Department of Energy’s SLAC National Accelerator Laboratory have exploited this Schroedinger’s Cat behavior to create X-ray movies of atomic motion with much more detail than ever before.

The first test of this idea, at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, created the world’s most detailed X-ray movie of the inner machinery of a molecule – in this case, a two-atom molecule of iodine. The results, based on an experiment led by SLAC staff scientist Mike Glownia, were reported in a paper that’s been posted on the arXiv online repository and accepted for publication in Physical Review Letters.

An animation explains the basic concept behind using ‘Schroedinger’s Cat’ states to make a molecular movie. (SLAC National Accelerator Laboratory)

Zooming in on Atomic Vibrations

The team was able to see details of the molecule’s behavior as small as .3 angstrom ­– less than the width of an atom – and as brief as 30 millionths of a billionth of a second, a timescale that captures the vibrations of atoms and molecules. What’s more, they say their method can be retroactively applied to data from past experiments, not just to future studies.

“Our method is fundamental to quantum mechanics, so we are eager to try it on other small molecular systems, including systems involved in vision, photosynthesis, protecting DNA from UV damage and other important functions in living things,” said Phil Bucksbaum, a professor at SLAC and Stanford University and director of PULSE, which is jointly operated by the lab and the university.

The new technique is based on the fact that when a molecule absorbs a short burst of energy, it splits into two versions of itself – one excited, the other not. A follow-up burst of X-ray laser light scatters off both versions of the molecule and recombines to form an X-ray hologram that, after some clever processing, reveals the excited state of the molecule in stunning detail. By stringing together a series of these X-ray snapshots, scientists can make a stop-action movie.

“Our movie, which is based on images from billions of iodine gas molecules, shows all the possible ways the iodine molecule behaves when it’s excited with this amount of energy,” Bucksbaum said.

“We see it start to vibrate, with the two atoms veering toward and away from each other like they were joined by a spring. At the same time, we see the bond between the atoms break, and the atoms fly off into the void. Simultaneously we see them still connected, but hanging out for a while at some distance from each other before moving back in. As time goes on, we see the vibrations die down until the molecule is at rest again. All these possible outcomes happen within a few trillionths of a second.”

This movie, derived from LCLS data, shows an iodine molecule moving in the first 2 trillionths of a second after being excited by a laser pulse. The clouds of blue dots represent the molecule’s two atoms, at top and bottom, which are joined by a bond through the middle. As the molecule starts to vibrate, the atoms oscillate back and forth. In some cases the bonds break and the atoms fly away. Clouds of red dots represent atoms in the unexcited state of the molecule, which exists simultaneously with its excited state in a Schroedinger’s Cat-like quantum paradox. (J.M. Glownia et al., Physical Review Letters)

Using Cat States to Make a Movie

Although the initial laser pulse hits only 4 or 5 percent of the molecules in the iodine gas cloud, it would be incorrect to say that only this small fraction was excited and the rest were not, Bucksbaum added. In quantum mechanical terms, every single molecule was excited a little bit, like a Schroedinger’s Cat that’s both dead and alive.

This dual state was key to making the molecular movie. It allowed the X-rays to bounce off both states of a molecule at once and recombine to form a hologram – a pattern of concentric rings that are brighter where the two signals reinforce each other and darker where they cancel each other out. The fact that this pattern formed in the LCLS detector proves that the excited and unexcited states were simultaneously present in each and every molecule, Bucksbaum said; if they had been separated by even a tiny distance, the pattern could not have formed.

The team used mathematical techniques borrowed from atomic physics to amplify the signal from the excited state, which would form the basis of the movie. But the signal from the unexcited state also played an important role, serving as a reference point that helped them reconstruct the behavior of the excited molecule in three dimensions in a process known as “phasing.”

Any group of molecules hit with a laser pulse will respond the same way, splitting into the equivalent of live and dead cats, Bucksbaum said. But the process can only be clearly and directly observed with intense, ultrashort pulses of coherent light like those from an X-ray laser, and until now no one had thought to take advantage of the Schroedinger’s Cat connection to sharpen images taken with X-rays.

“The X-ray diffraction community had never used these tools the way we did,” said Adi Natan, a PULSE research associate and experimental physicist who led that part of the project. He said the team is already applying their method to data from previous experiments at LCLS to see if they can create more molecular movies.

LCLS is a DOE Office of Science User Facility. The research was funded by the DOE Office of Science and included scientists from PULSE, LCLS and Stanford.