Producing hydrogen in a sustainable way is a challenge and production cost is too high. A team led by EPFL Professor Xile Hu has discovered that a molybdenum based catalyst is produced at room temperature, inexpensive and efficient. The results of the research are published online in Chemical Science Thursday the 14th of April. An international patent based on this discovery has just been filled.

Existing in large quantities on Earth, water is composed of hydrogen and oxygen. It can be broken down by applying an electrical current; this is the process known as electrolysis. To improve this particularly slow reaction, platinum is generally used as a catalyst. However, platinum is a particularly expensive material that has tripled in price over the last decade. Now EPFL scientists have shown that amorphous molybdenum sulphides, found abundantly, are efficient catalysts and hydrogen production cost can be significantly lowered.

Industrial prospects

The new catalysts exhibit many advantageous technical characteristics. They are stable and compatible with acidic, neutral or basic conditions in water. Also, the rate of the hydrogen production is faster than other catalysts of the same price. The discovery opens up some interesting possibilities for industrial applications such as in the area of solar energy storage.

Using a molybdenum based catalyst, hydrogen bubbles are made cheaply and at room temperature. Credit: EPFL / Alain Herzog

It's only by chance that Daniel Merki, Stéphane Fierro, Heron Vrubel and Xile Hu made this discovery during an electrochemical experience. "It's a perfect illustration of the famous serendipity principle in fundamental research", as Xile Hu emphasizes: "Thanks to this unexpected result, we've revealed a unique phenomenon", he explains. "But we don't yet know exactly why the catalysts are so efficient."

The next stage is to create a prototype that can help to improve sunlight-driven hydrogen production. But a better understanding of the observed phenomenon is also required in order to optimize the catalysts.
 
Source: PhysOrg

More information: Daniel Merki, Stéphane Fierro, Heron Vrubel and Xile Hu, "Amorphous Molybdenum Sulfide Films as Catalysts for Electrochemical Hydrogen Production in Water," Chemical Science, 2011.

A report, published in the March 14 edition of the Journal of Materials Chemistry, announced the successful fabrication and testing of a new type solar cell using an inorganic core/shell nanowire structure.
Arrays of core/shell nanowires (described has "quantum coaxial cables") had previously been theorized as a potential structure that, while composed of chemically more stable large bandgap inorganic materials, should also be capable of absorbing the broad range of the wavelengths present in sunlight. High bandgap semiconductors are generally considered not effective at absorbing most of the available wavelengths in solar radiation by themselves. For instance, high bandgap zinc oxide (ZnO) is transparent in the visible but absorptive in the ultraviolet range, and thus is widely used in sunscreens but was not considered useful in solar cells.

In the report, a team of researchers from Xiamen University in China and the University of North Carolina at Charlotte describe successfully creating zinc oxide (ZnO) nanowires with a zinc selenide (ZnSe) coating to form a material structure known as a type-II heterojunction that has a significantly lower bandgap than either of the original materials. The team reported that arrays of the structured nanowires were subsequently able to absorb light from the visible and near-infrared wavelengths, and show the potential use of wide bandgap materials for a new kind of affordable and durable solar cell.
"High bandgap materials tend to be chemically more stable than the lower bandgap semiconductors that we currently have," noted team member Yong Zhang, a Bissell Distinguished Professor in the Department of Electrical and Computer Engineering and in the Energy Production and Infrastructure Center (EPIC) at the University of North Carolina at Charlotte.

"And these nanowire structures can be made using a very low cost technology, using a chemical vapor deposition (CVD) technique to grow the array," he added. "In comparison, solar cells using silicon and gallium arsenide require more expensive production techniques."
Based on a concept published in Nano Letters in 2007 by Zhang and collaborators Lin-Wang Wang (Lawrence Berkeley National Laboratory) and Angelo Mascarenhas (National Renewable Energy Laboratory), the array was fabricated by Zhang's current collaborators Zhiming Wu, Jinjian Zheng, Xiangan Lin, Xiaohang Chen, Binwang Huang, Huiqiong Wang, Kai Huang, Shuping Li and Junyong Kang at the Fujian Key Laboratory of Semiconductor Materials and Applications in the Department of Physics at Xiamen University, China.

Past attempts to use high band gap materials did not actually use the semiconductors to absorb light but instead involved coating them with organic molecules (dyes) that accomplished the photo absorption and simply transmitted electrons to the semiconductor material. In contrast, the team's heterojunction nanowires absorb the light directly and efficiently conduct a current through nano-sized "coaxial" wires, which separate charges by putting the excited electrons in the wires' zinc oxide cores and the "holes" in the zinc selenide shells.
"By making a special heterojunction architecture at the nanoscale, we are also making coaxial nanowires which are good for conductivity," said Zhang. "Even if you have good light absorption and you are creating electron-hole pairs, you need to be able to take them out to the circuit to get current, so we need to have good conductivity. These coaxial nanowires are similar to the coaxial cable in electrical engineering. So basically we have two conducting channels -- the electron going one way in the core and the hole going the other way in the shell."

The nanowires were created by first growing an array of six-sided zinc oxide crystal "wires" from a thin film of the same material using vapor deposition. The technique created a forest of smooth-sided needle-like zinc oxide crystals with uniform diameters (40 to 80 nanometers) along their length (approximately 1.4 micrometers). A somewhat rougher zinc selenide shell was then deposited to coat all the wires. Finally, an indium tin oxide (ITO) film was bonded to the zinc selenide coating, and an indium probe was connected to the zinc oxide film, creating contacts for any current generated by the cell.
"We measured the device and showed the photoresponse threshold to be 1.6 eV," Zhang said, noting that the cell was thus effective at absorbing light wave wavelengths from the ultraviolet to the near infrared, a range that covers most of the solar radiation reaching earth's surface.

Though the use of the nanowires for absorbing light energy is an important innovation, perhaps even more important is the researchers' success in using stable high bandgap inorganic semiconductor materials for an inexpensive but effective solar energy device.

"This is a new mechanism, since these materials were previously not considered directly useful for solar cells," Zhang said. He stressed that the applications for the concept do not end there but open the door to considering a larger number of high bandgap semiconductor materials with very desirable material properties for various solar energy related applications, such as hydrogen generation by photoelectrochemical water splitting.
"The expanded use of type II nanoscale heterostructures also extends their use for other applications as well, such as photodetectors -- IR detector in particular," he noted.
 
Source: ScienceDaily

If your asthma is acting up, you’re probably not the only one. But unless you’re standing next to someone who is also huffing his or her inhaler, you wouldn’t know it. That’s a problem for epidemiologists who do their best work when they’re buried in data, and it’s exactly the problem a former Centers for Disease Control and Prevention (CDC) researcher aims to solve with a GPS- and WiFi-enabled inhaler.

The Ubiquitous Inhaler is Getting a Digital Upgrade - Mendel via Wikimedia

Asthma attacks can happen anywhere, but the causes of these attacks can be hard to pin down because patients don’t always report, or even remember, every time they pop their inhaler out for some respiratory relief. Dr. David Van Sickle’s Spiroscout inhaler aims to change this. Suck on the Spiroscout and it logs the time and position, sending it to a central computer for analysis.

That analysis benefits asthma sufferers on two levels. Individually, it allows participating patients and their doctors to analyze their inhaler use, shedding light on patterns that may develop in inhaler usage or indicating that perhaps the patient needs an adjustment in his or her medication.

But the larger benefit is societal. Once the data is stripped of identifying information, epidemiologists can analyze trends among entire groups of asthma sufferers. From this, they should be able to identify certain environmental and geographical factors--areas where certain plants are present or where certain pollutants are peristent--that precipitate asthma attacks. That could lead not only to a better understanding of asthma, but to a better understanding of the general air quality in a given area.

Source: PopSci

By cleverly linking five Wii Balance Boards, a team of Rice University undergraduates has combined the appeal of a video game with the utility of a computerized motion-tracking system that can enhance the progress of patients at Shriners Hospital for Children-Houston.

The Rice engineering students created the new device using components of the popular Nintendo game system to create a balance training system.

Custom sensors built by Rice engineering students are part of the active handrails that provide force feedback on how heavily patients are depending on their arms as they perform balancing tasks on the Wii boards. Credit: Jeff Fitlow/Rice University

What the kids may see as a fun video game is really a sophisticated way to help them advance their skills. The Wii Balance Boards lined up between handrails will encourage patients age 6 to 18 to practice their balance skills in an electronic gaming environment. The active handrails, which provide feedback on how heavily patients depend on their arms, are a unique feature.

Many of the children targeted for this project have cerebral palsy, spina bifida or amputations. Using the relatively inexpensive game console components improves the potential of this system to become a cost-effective addition to physical therapy departments in the future.

Steven Irby, an engineer at Shriners' Motion Analysis Laboratory, pitched the idea to Rice's engineering mentors after the success of last year's Trek Tracker project, a computer-controlled camera system for gait analysis that was developed by engineering students at Rice's Oshman Engineering Design Kitchen (OEDK).

The engineering seniors who chose to tackle this year's new project -- Michelle Pyle, Drew Berger and Matt Jones, aka Team Equiliberators -- hope to have the system up and running at Shriners Hospital before they graduate next month.

"He (Irby) wants to get kids to practice certain tasks in their games, such as standing still, then taking a couple of steps and being able to balance, which is pretty difficult for some of them," Pyle said. "The last task is being able to take a couple of steps and then turn around."

"This isn't a measurement device as much as it is a game," Irby said. "But putting the two systems together is what makes it unique. The Wii system is not well suited to kids with significant balance problems; they can't play it. So we're making something that is more adaptable to them."

The game requires patients to shoot approaching monsters by hitting particular spots with their feet as they step along the Wii array, computer science student Jesus Cortez, one of the game's creators, explained. The game gets harder as the patients improve, he said, and the chance to rack up points gives them an incentive.

A further step, not yet implemented, would be to program feedback from the handrails into the game. Leaning on the rails would subtract points from the users' scores, encouraging them to improve their postures. The game would also present challenges specific to younger and older children to keep them engaged.

The programming team also includes undergraduate Irina Patrikeeva and graduate student Nick Zhu. Studio arts undergraduate Jennifer Humphreys created the artwork.

Team Equiliberator combines engineering, computer science and art students in a project that uses Wii Balance Boards, a handrail sensor system and custom game software to help patients at Shriners Hospital for Children-Houston develop their balance. Clockwise from left: Matt Jones, Drew Berger, Jesus Cortez, Nick Zhu, Irina Patrikeeva, Michelle Pyle and Jennifer Humphreys. Credit: Jeff Fitlow/Rice University

The system's components include a PC, the Wii boards (aligned in a frame) and two balance beam-like handrails that read how much force patients are putting on their hands. Communications to the PC are handled via the Wii's native Bluetooth protocol.

The students said their prototype cost far less than the $2,000 they'd budgeted. Rice supplied the computer equipment and LabVIEW software they needed to create the diagnostic software that interfaces with Shriners' existing systems, and they purchased the Wii Balance Boards on eBay.

"Small force plates that people commonly use for such measurements cost at least a couple of grand, but Wii boards -- and people have done research on this -- give you a pretty good readout of your center of balance for what they cost," Pyle said.

Jones, who is building the final unit for delivery to Shriners, said he wants patients to see the Wii boards. "We're putting clear acrylic over the boards so there aren't any gaps that could trip up the younger ones," he said. "We wanted to use a device that's familiar to them, but they might not be convinced it's a Wii board unless they can see it."

Source: physorg - Research provided by Rice University

In a development that holds intriguing possibilities for the future of industrial catalysis, as well as for such promising clean green energy technologies as artificial photosynthesis, researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have created bilayered nanocrystals of a metal-metal oxide that are the first to feature multiple catalytic sites on nanocrystal interfaces. These multiple catalytic sites allow for multiple, sequential catalytic reactions to be carried out selectively and in tandem.

Transmission electron micrograph showing monolayer of a cerium oxide nanocube monolayer on a platinum monolayer in a new bilyaer nanocatalyst. Credit: Image courtesy of Yang group

"The demonstration of rationally designed and assembled nanocrystal bilayers with multiple built-in metal–metal oxide interfaces for tandem catalysis represents a powerful new approach towards designing high-performance, multifunctional nanostructured catalysts for multiple-step chemical reactions," says the leader of this research Peidong Yang, a chemist who holds joint appointments with Berkeley Lab's Materials Sciences Division, and the University of California Berkeley's Chemistry Department and Department of Materials Science and Engineering.

Yang is the corresponding author of a paper describing this research that appears in the journal Nature Chemistry. The paper is titled "Nanocrystal bilayer for tandem catalysis."

Co-authoring the paper were Yusuke Yamada, Chia-Kuang Tsung, Wenyu Huang, Ziyang Huo, Susan Habas, Tetsuro Soejima, Cesar Aliaga and leading authority on catalysis Gabor Somorjai.

Catalysts – substances that speed up the rates of chemical reactions without themselves being chemically changed – are used to initiate virtually every industrial manufacturing process that involves chemistry. Metal catalysts have been the traditional workhorses, but in recent years, with the advent of nano-sized catalysts, metal,oxide and their interface have surged in importance.

"High-performance metal-oxide nanocatalysts are central to the development of new-generation energy conversion and storage technologies," Yang says. "However, to significantly improve our capability of designing better catalysts, new concepts for the rational design and assembly of metal–metal oxide interfaces are needed."

Studies in recent years have shown that for nanocrystals, the size and shape – specifically surface faceting with well-defined atomic arrangements – can have an enormous impact on catalytic properties. This makes it easier to optimize nanocrystal catalysts for activity and selectivity than bulk-sized catalysts. Shape- and size-controlled metal oxide nanocrystal catalysts have shown particular promise.

In a unqiue new bilyaer nanocatalyst system, single layers of metal and metal oxide nanocubes are deposited to create two distinct metal-metal oxide interfaces that allow for multiple, sequential catalytic reactions to be carried out selectively and in tandem. Credit: Image courtesy of Yang group

"It is well-known that catalysis can be modulated by using different metal oxide supports, or metal oxide supports with different crystal surfaces," Yang says. "Precise selection and control of metal-metal oxide interfaces in nanocrystals should therefore yield better activity and selectivity for a desired reaction."

To determine whether the integration of two types of metal oxide interfaces on the surface of a single active metal nanocrystal could yield a novel tandem catalyst for multistep reactions, Yang and his coauthors used the Lamgnuir-Blodgett assembly technique to deposit nanocube monolayers of platinum and cerium oxide on a silica (silicon dioxide) substrate. The nanocube layers were each less than 10 nanometers thick and stacked one on top of the other to create two distinct metal–metal oxide interfaces – platinum-silica and cerium oxide-platinum. These two interfaces were then used to catalyze two separate and sequential reactions. First, the cerium oxide-platinum interface catalyzed methanol to produce carbon monoxide and hydrogen. These products then underwent ethylene hydroformylation through a reaction catalyzed by the platinum-silica interface. The final result of this tandem catalysis was propanal.

"The cubic shape of the nanocrystal layers is ideal for assembling metal–metal oxide interfaces with large contact areas," Yang says. "Integrating binary nanocrystals to form highly ordered superlattices is a new and highly effective way to form multiple interfaces with new functionalities."

Yang says that the concept of tandem catalysis through multiple interface design that he and his co-authors have developed should be especially valuable for applications in which multiple sequential reactions are required to produce chemicals in a highly active and selective manner. A prime example is artificial photosynthesis, the effort to capture energy from the sun and transform it into electricity or chemical fuels. To this end, Yang leads the Berkeley component of the Joint Center for Artificial Photosynthesis, a new Energy Innovation Hub created by the U.S. Department of Energy that partners Berkeley Lab with the California Institute of Technology (Caltech).

"Artificial photosynthesis typically involves multiple chemical reactions in a sequential manner, including, for example, water reduction and oxidation, and carbon dioxide reduction," says Yang. "Our tandem catalysis approach should also be relevant to photoelectrochemical reactions, such as solar water splitting, again where sequential, multiple reaction steps are necessary. For this, however, we will need to explore new metal oxide or other semiconductor supports, such as titanium dioxide, in our catalyst design."

Source: PhysOrg

Advances made by researchers at Los Alamos National Laboratory could enhance the ability of scientists to develop advanced nuclear fuels in a safer, simpler manner.

Uranium chemistry research relies heavily on a variety of uranium "starting materials"—solids and solutions—that are precursors to uranium compounds of oxygen, nitrogen, halogen, carbon, fluorine, and other elements, all of which are candidates for advanced nuclear fuels.

Uranium also has been identified as a promising material in developing superconductors, and for use as catalysts—to speed up other chemical reactions.

But uranium starting materials have traditionally been relatively difficult or hazardous to produce.  Now researchers at Los Alamos National Laboratory have developed a method to produce uranium starting materials in a much more benign fashion. The method, recently published in the scientific journal Organometallics, relies on a room-temperature process that reacts uranium metal in a solution of 1,4-dioxane – a liquid organic solvent – and iodine.

Conventional methods of producing uranium starting materials can require toxic chlorine-containing compounds and high temperatures or mercury iodide and low temperatures.  Some of these syntheses are dangerous and generate a fair amount of waste.

“A major barrier to widespread uranium chemistry research has been access to these starting materials,” said Jaqueline Kiplinger, lead scientist on the research.  “Easy access to uranium(III) and -(IV) precursors can change the way people do uranium work because there is less waste, and it’s simpler, cleaner, safer, and faster.”

The synthesis involves placing readily available metal uranium shavings in a liquid bath of 1,4-dioxane and iodine at room temperature and stirring.  The result is either UI3(1,4-dioxane)1.5 or UI4(1,4-dioxane)2, both called uranium iodides.  Both waste little of the original uranium and are highly resistant to degradation.  Further, these starting materials have been used to make many other uranium compounds that are valuable in uranium research.

“It’s my belief that these developments will open doors to a variety of new uranium research areas,” said Kiplinger.”

In a recent edition of the magazine Chemistry World, Stephen Liddle, a uranium chemistry researcher in the United Kingdom, agreed. “Historically this area has lagged behind many others, and one reason is the lack of suitable precursor materials,” he said. ”Hopefully these alternative uranium halides will help open up the area in general by leading to new compounds.”

The research team includes Marisa Monreal, a Seaborg Graduate Student Fellow at Los Alamos, Robert Thomson and Nicholas Travia, both Seaborg Postdoctoral Fellows at Los Alamos, Thibault Cantat, Brian Scott and Jaqueline Kiplinger (all of materials physics & applications division). The research was supported by the DOE Office of Science-Heavy Element Chemistry program, the Los Alamos Laboratory Directed Research and Development program, and through Los Alamos National Laboratory Director’s and G.T. Seaborg Institute for Transactinium Science Postdoctoral Fellowships.

The Chemistry World article is available at HERE.

The Organometallics research paper is available HERE.

Find out more about Los Alamos National Laboratory HERE.

Architect Eugene Tsui is taking the gigantic volcano tower concept to a whole new eco level, by taking design inspiration from the natural world. His new design for the Ultima Tower – a 2-mile high Mt Doom-esque structure – borrows design principles from trees and other living ystem to reduce its energy footprint.

We are always intrigued by architecture that uses biomimicry – the borrowing of principles from nature’s designs – and Tsui’s concept for this towering, ultra-dense urban development has certainly captured our attention with its thought-provoking design.

Population growth rates and rural-urban migration are creating a trend of chaotic urbanization that brings environmental, economic and social challenges. Within the next 7 years, 22 megacities across the globe are expected to have populations that exceed 10 million people, according to the UN. The Ultima Tower is an innovative green design concept proposed to resourcefully use earth’s surface and allow sustainable distribution of resources within a dense urban setting.

Designed to withstand natural calamities, Ultima Tower is highly stable and aerodynamic. Rather than spreading horizontally the structure rises vertically from a base with a 7,000 foot diameter – inspired in part by the termite’s nest structures of Africa, the highest structure created by any living organism.

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Surrounded on all sides by a lake, the building would use building integrated photo-voltaic solar cells to meet most of the electrical energy requirements. The tower would also use Atmospheric Energy Conversion to exploit the differences in atmospheric pressure at the bottom and top of the tower and convert this differential into electrical power. Wind turbine energy would also be used to power the tower.

Taking a cue from the principles of transpiration and cohesion (Joly-Dixon’s cohesion-tension theory) as used by the tree to move water from roots to aerial parts, the designers are working on a method of carrying water from the bottom of the tower to the top utilizing water potential difference between the two points.

Other significant features of the design include bodies of water placed at 12 separate levels, 144 elevators at the periphery of the building, use of vertical propulsion through compressed air, specially designed windows with aerodynamic wind cowls, reflecting mirrors to bring direct sunlight into the building, open garden balconies, electric cars run by propane and hydrogen gas, complete absence of internal combustion engines or toxic pollutants. The whole building is envisioned by Tsui as a large ecosystem teeming with structures that are ‘living and breathing’.

Source: Inhabitat

It's billed as the wonder material of the 21st century with the power to revolutionise micro-electronics, and won its pioneers the 2010 Nobel Physics Prize.

Professor Jacek Baranowski of the Institute of Electronic Materials Technology (ITME) in Warsaw poses on April 7 [Image], near a laser in the Polish capital. Baranowski 's team says it has discovered a new method to produce entire layers of graphene, a move that should help to propel it out of the lab and into everyday life.

Now Polish scientists say they have discovered a new method to produce entire layers of graphene, a move that should help to propel it out of the lab and into everyday life.

Professor Jacek Baranowski of the Institute of Electronic Materials Technology (ITME) in Warsaw poses on April 7, near a laser in the Polish capital. Baranowski 's team says it has discovered a new method to produce entire layers of graphene, a move that should help to propel it out of the lab and into everyday life.

Just one atom thick, the novel form of carbon is the world's thinnest and strongest nano-material, almost transparent and able to conduct electricity and heat.

"This is an important step forward on the path to the production of transistors and then integrated circuits made of graphene," Professor Jacek Baranowski of the Institute of Electronic Materials Technology (ITME) in Warsaw told AFP.

Russian-born, British-based researchers Andre Geim and Konstantin Novoselov were honoured with a Nobel last October for their pioneering work.

Graphene transistors would in theory be able to run at faster speeds and cope with higher temperatures than today's classic silicon computer chips.

That would resolve a fast-growing problem facing chip engineers who want to boost power and shrink semiconductor size but without raising temperatures, the bugbear of computing.

Graphene's transparency also means it could potentially be used in touch screens and even solar cells, and when mixed with plastics would provide light but super-strong composite materials for next-generation satellites, planes and cars.

Electrons can travel relatively huge distances through graphene -- a thousandth of a millimetre is a lot in their world -- without being hampered by impurities which are a problem in the silicon used in 95 percent of electronic devices.

They also pick up speeds of 1,000 kilometres (620 miles) per second in graphene, some 30 times faster than in silicon.

Graphene is also 200 times tougher than steel.

But the catch so far has been a lack of methods to turn out layers of it, and that is where the work of Baranowski's research team come in.

"The new method is based on using the technique of epitaxy on silicon carbide in a gaseous, pressurised environment," said Baranowski, who also works at the University of Warsaw's experimental physics faculty.

Epitaxy is a technique for growing a micro-thin, honeycomb-shaped lattice of the desired material.

While it is currently possible to produce graphene layers, relatively large ones can only be made on a metal base. That hampers graphene's electronics potential.

Without such a base, current techniques only allow for a maximum layer surface of four square inches (25 square centimetres).

Current methods also fail to produce graphene as uniform as that devised by Baranowski's team, he said.

It is precisely that uniformity that would make graphene more readily usable in the hi-tech sector, he added.

The team's discovery was announced in the most recent edition of the US scientific periodical Nano Letters. It is set to be presented at a conference starting Monday in Bilbao, Spain.

ITME's research was carried out under the wing of the European Science Foundation, which groups 78 organisations in 30 nations.

It is part of a wider project aimed at producing a graphene transistor, along with researchers in the Czech Republic, France, Germany, Sweden and Turkey.

Source: PhysOrg

Some 300 exabytes (3 × 1020 bytes) of information were stored in electronic media -- magnetic disks and tapes or optical disks -- throughout the world by 2007. Yet, the demand for electronic storage grows daily, driving an ever-increasing need to pack data into smaller volumes in quicker time. By studying how laser pulses alter the atomic structure of data-storage materials, a research team in Japan has uncovered a fundamental mechanism that could aid in the design of even faster information storage in the future1. The finding was published by Masaki Takata from the RIKEN SPring-8 Center, Harima, Shinji Kohara from the Japan Synchrotron Radiation Research Institute/SPring-8, Noboru Yamada from Panasonic Corporation and a team of scientists from Japan, Germany and Finland.

Pulses of light alter the atomic bonds (red) in the material AIST, enabling quick storage and deletion of data. Credit: 2011 Masaki Takata

Rewritable memory, such as the random-access memory found in computers or on DVDs, is based on a phase change in specific types of materials in which the atoms change from one stable arrangement to another. Pulses of laser light can induce a phase change, a process known as ‘writing,’ and the material’s phase can be identified by ‘reading’ its signature optical properties.

To provide the first full understanding of the atomic structure of one such phase-change material, AgInSbTe (AIST)—often used in rewritable DVDs—Takata and his colleagues combined state-of-the-art materials-analysis techniques and theoretical modeling. A pulse of light can change AIST from an amorphous state, in which the atoms are disordered, into a crystalline phase in which the atoms are form an ordered-lattice structure. This process of crystallization happens in just a few tens of nanoseconds: the faster the crystallization, the faster data can be written and erased. No-one understood, however, why phase changes in AIST were so fast.

The teams’ analyses and modeling showed that AIST crystallizes in a different way to other commercially available phase-change materials. They found that crystallization of AIST is a simple process: the laser light excites the bonding electrons and causes them to move. A central atom of antimony (Sb) switches between one long (amorphous) and one short (crystalline) bond without any bond breaking (Fig. 1). “We hope to verify this bond-interchange model in the near future,” says Takata. “Crystallization is the storage-rate-limiting process in all phase-change materials, and an atomistic understanding of it is essential.”

The researchers also discovered that the absence of cavities within the crystal structure contributes to the faster writing speeds on AIST. This contrasts starkly with the alternative material germanium antimony telluride in which 10% of lattice sites in are empty.

Source: PhysOrg

Time to retire the old soldering iron? In the "atomtronic" circuits pictured on the right, it is atoms, not electrons, that flow. Such circuits could form the basis for ultra-sensitive gyroscopes.

Previously, atoms have been made to flow from one point to another. To get them to flow round and round in a circuit, Kevin Wright and colleagues at the National Institute of Standards and Technology in Gaithersburg, Maryland, chilled 100,000 sodium atoms until they became a Bose-Einstein condensate – a blob of floating atoms that behaves as a single, coherent quantum object.

The researchers used a complex array of lasers to trap and shape the blob into a torus. A further pair of lasers, one in a rotating configuration, gave the atoms just enough energy to circulate in unison around the ring, but not so much energy that the condensate decohered.

This "current" of atoms flowed for 40 seconds, four times longer than atoms in previous experiments.

Superfluid gyroscope

Flowing atoms act like frictionless "superfluids"", which are highly sensitive to rotation, so such atomtronic circuits might be used to build ultra-sensitive gyroscopes, says Wright.

His team also pinched off part of the torus with another laser, restricting the flow of atoms, but not stopping them entirely. In electrical circuits, the closest analogy to this is a Josephson junction, a gap over which current flows between two superconductors. These form the basis of superconducting quantum interference devices (SQUIDS), which are used to measure magnetic fields with high sensitivity.

Matthew Davis, a physicist at the University of Queensland in Brisbane, Australia, calls the new work "impressive" and agrees that it could eventually lead to "practical devices that are extremely sensitive for the detection of rotational or gravitational forces".

Source: NewScientist