The proof is in the pudding

There is an important difference between knowing something, and being able to prove something. Even in science, there are ideas that everyone shares, but no one can prove.

The link between disorder and metastability in a granular material was one of such ideas, until three researchers devised an experiment to measure the relationship between the two phenomena.

Prof Mahesh Bandi, lead researcher of the Collective Interactions Unit at theOkinawa Institute of Science and Technology Graduate University (OIST), is one of these three researchers. Together with two colleagues from Nagoya University, Naoki Iikawa and Prof Hiroaki Katsuragi, Prof Bandi has recently published inPhysical Review Letters, showing for the first time that it is possible to detect and quantify metastability induced by disorder. "Everyone expected this result," said Bandi, "but before us no one was able to find a way to measure the relationship between disorder and metastability in granular materials."

Metastability is a concept linked with the level of energy in a physics system. When a physics system is stable, it has only one state of low energy. Its energy is like a bucket in a well: when it goes down, it will always end up in the same water pool.

But there are physics systems that can be equated to strange wells. Wells that have many water pools at their bottom. When the bucket goes down in one of these wells, it is not possible to predict with certainty in which pool it will end up. Furthermore, if the bucket is lifted to any height in the well and then released, it may end up in a different pool. These physics systems are metastable: the lowest state of energy for these systems is neither unique nor predictable.

The relationship between metastability and disorder was elusive since the measurements typically used in granular physics are not sensitive enough to detect metastability. Bandi and colleagues succeeded because they thought out of the box. They borrowed a parameter, called 'S', from a different branch of physics, liquid crystal physics. They showed that S can be used to detect the orientation of the forces inside a granular material. These forces, called force chains, are the networks of forces that arise from the contacts among grains. Force chains give granular materials their physical proprieties. To study force chains, the scientists used special disks, called photo-elastic disks, which change their appearance when compressed.

After checking that in an ordered configuration there was no change in S, the scientists set up a random configuration of photo-elastic disks. They took disks of two different diameters, and inserted them in a vertical structure. Inside such configuration, the force chains pointed along any direction. "Then, we tapped the structure," Bandi recollects, "hitting it along the vertical direction."

The configuration of the disks stayed the same, but the force chains slowly oriented themselves from the direction of gravity towards all random directions. The scientists captured high-resolution images of this process. The images showed the changing force chains, and the researchers translated the visual information into numbers. The resulting values of S confirmed the change in the force chains, finally proving the link between disorder, induced by tapping, and the metastable energy state of the granular material, which changed after each tapping like a bucket changing pool in one of those strange wells.

While this result was expected, the introduction of S, the parameter from liquid crystal, represents an important change in the study of granular materials. S switches the focus from the structure of granular materials, to the orientation of the force chains inside granular materials. Such switch of focus provides the researchers with a new way to conceptualize disorder and metastability in granular materials, hopefully leading to new advances in the understanding of these materials.

Reference:

Sensitivity of Granular Force Chain Orientation to Disorder-Induced Metastable Relaxation
N. Iikawa, M. M. Bandi, and H. Katsuragi
Phys. Rev. Lett. 116, 128001 – Published 21 March 2016
DOI: http://dx.doi.org/10.1103/PhysRevLett.116.128001

Okinawa Institute of Science and Technology Graduate University OIST

Nanotechnologists at UT make orientation of magnetism adjustable in new materials

New material offers potential for data storage and spintronics applications

 

Nanotechnologists at the UT research institute MESA+ are now able to create materials in which they can influence and precisely control the orientation of the magnetism at will. An interlayer just 0.4 nanometres thick is the key to this success. 

The materials present a range of interesting possibilities, such as a new way of creating computer memory as well as spintronics applications – a new form of electronics that works on the basis of magnetism instead of electricity. The research was published today in the leading scientific journal Nature Materials. 

Nanotechnologists at the University of Twente are specialized in creating new materials. Thanks to the top-level facilities at the MESA+ NanoLab they are able to combine materials as they wish, with the ability to control the material composition down to atom level. In particular, they specialize in creating materials composed of extremely thin layers, sometimes just one atom thick. 

Computer memory

 

In research published today in the scientific journal Nature Materials, they show their ability to create new materials within which they can precisely and locally control the orientation of the magnetism. This opens the way to new possibilities of creating computer memory. Moreover, this method of creating materials is interesting for spintronics, a new form of electronics that does not utilize the movement of charges but instead the magnetic properties of a material. This not only makes electronics very fast and efficient, but also allows them to be produced in extremely small dimensions.  

Interlayer

 

In the course of this research the scientists stacked up various thin layers of Perovskite materials. By placing an extremely thin interlayer of just 0.4 nanometres between the layers (a nanometre is a million times smaller than a millimetre), it becomes possible to influence the orientation of the magnetism in the individual Perovskite layers as desired, whereby the orientation of the magnetism in the bottom layer, for instance, is perpendicular to that of the layer above. By varying the location where the interlayer is applied, it becomes possible to select the local orientation of the magnetism anywhere in the material. This is an essential property for new forms of computer memory and for spintronics applications. This effect was already known for much thicker layers, but never before had researchers demonstrated that the orientation of the magnetism can be controlled so precisely with extremely thin layers, too. 

Research

 

The research has been conducted by scientists of the MESA+ research groupInorganic Materials Science in collaboration with colleagues from other institutes, including the University of Antwerp (Belgium), the University of British Columbia (Canada) and TU Wien (Vienna, Austria). Within the research project, the Twente-based researchers were responsible for coordination and for creating the materials. The colleague researchers from Antwerp visualized the materials and were able to image even the smallest atoms in the material. The Canadian researchers created a magnetic cross-section of the material, while the Austrian researchers handled the theoretical calculations.

The research is published under the title ‘Controlled lateral anistropy in correlated manganite heterostructures by interface-engineered oxygen octahedral coupling’ by Z. Liao, M. Huijben, Z. Zhong, N. Gauquelin, S. Macke, R. J. Green, S. Van Aert, J. Verbeeck, G. Van Tendeloo, K. Held, G. A. Sawatzky, G. Koster and G. Rijnders.

MESA+ Institute for Nanotechnology

UCLA researchers create exceptionally strong and lightweight new metal

Magnesium infused with dense silicon carbide nanoparticles could be used for airplanes, cars, mobile electronics and more

A team led by researchers from the UCLA Henry Samueli School of Engineering and Applied Science has created a super-strong yet light structural metal with extremely high specific strength and modulus, or stiffness-to-weight ratio. The new metal is composed of magnesium infused with a dense and even dispersal of ceramic silicon carbide nanoparticles. It could be used to make lighter airplanes, spacecraft, and cars, helping to improve fuel efficiency, as well as in mobile electronics and biomedical devices.

To create the super-strong but lightweight metal, the team found a new way to disperse and stabilize nanoparticles in molten metals. They also developed a scalable manufacturing method that could pave the way for more high-performance lightweight metals. The research waspublished today in Nature. 

“It’s been proposed that nanoparticles could really enhance the strength of metals without damaging their plasticity, especially light metals like magnesium, but no groups have been able to disperse ceramic nanoparticles in molten metals until now,” said Xiaochun Li, the principal investigator on the research and Raytheon Chair in Manufacturing Engineering at UCLA. “With an infusion of physics and materials processing, our method paves a new way to enhance the performance of many different kinds of metals by evenly infusing dense nanoparticles to enhance the performance of metals to meet energy and sustainability challenges in today’s society.”

Structural metals are load-bearing metals; they are used in buildings and vehicles. Magnesium, at just two-thirds the density of aluminum, is the lightest structural metal. Silicon carbide is an ultra-hard ceramic commonly used in industrial cutting blades. The researchers’ technique of infusing a large number of silicon carbide particles smaller than 100 nanometers into magnesium added significant strength, stiffness, plasticity and durability under high temperatures.

The researchers’ new silicon carbide-infused magnesium demonstrated record levels of specific strength — how much weight a material can withstand before breaking — and specific modulus — the material’s stiffness-to-weight ratio. It also showed superior stability at high temperatures.

Ceramic particles have long been considered as a potential way to make metals stronger. However, with microscale ceramic particles, the infusion process results in a loss of plasticity.

Nanoscale particles, by contrast, can enhance strength while maintaining or even improving metals’ plasticity. But nanoscale ceramic particles tend to clump together rather than dispersing evenly, due to the tendency of small particles to attract one other.

To counteract this issue, researchers dispersed the particles into a molten magnesium zinc alloy. The newly discovered nanoparticle dispersion relies on the kinetic energy in the particles’ movement. This stabilizes the particles’ dispersion and prevents clumping.

To further enhance the new metal’s strength, the researchers used a technique called high-pressure torsion to compress it.

“The results we obtained so far are just scratching the surface of the hidden treasure for a new class of metals with revolutionary properties and functionalities,” Li said.

The new metal (more accurately called a metal nanocomposite) is about 14 percent silicon carbide nanoparticles and 86 percent magnesium. The researchers noted that magnesium is an abundant resource and that scaling up its use would not cause environmental damage.

The paper’s lead author is Lian-Yi Chen, who conducted the research as a postdoctoral scholar in Li’s Scifacturing Laboratory at UCLA. Chen is now an assistant professor of mechanical and aerospace engineering at Missouri University of Science and Technology.

The paper’s other authors from UCLA include Jia-Quan Xu, a graduate student in materials science and engineering; Marta Pozuelo, an assistant development engineer; and Jenn-Ming Yang, professor of materials science and engineering.

The other authors on the paper are Hongseok Choi, of Clemson University; Xiaolong Ma, of North Carolina State University; Sanjit Bhowmick of Hysitron, Inc. of Minneapolis; and Suveen Mathaudhu of UC Riverside.

UCLA

A Nanoscale Look at Why a New Alloy is Amazingly Tough

Just in time for the icy grip of winter: A team of researchers led by scientists from the U.S. Department of Energy Lawrence Berkeley National Laboratory (Berkeley Lab) has identified several mechanisms that make a new, cold-loving material one of the toughest metallic alloys ever.

The alloy is made of chromium, manganese, iron, cobalt and nickel, so scientists call it CrMnFeCoNi. It’s exceptionally tough and strong at room temperature, which translates into excellent ductility, tensile strength, and resistance to fracture. And unlike most materials, the alloy becomes tougher and stronger the colder it gets, making it an intriguing possibility for use in cryogenic applications such as storage tanks for liquefied natural gas.

To learn its secrets, the Berkeley Lab-led team studied the alloy with transmission electron microscopy as it was subjected to strain. The images revealed several nanoscale mechanisms that activate in the alloy, one after another, which together resist the spread of damage. Among the mechanisms are bridges that form across cracks to inhibit their propagation. Such crack bridging is a common toughening mechanism in composites and ceramics but not often seen in unreinforced metals.

Their findings could guide future research aimed at designing metallic materials with unmatched damage tolerance. The research appears in the December 9, 2015, issue of the journal Nature Communications.

“We analyzed the alloy in earlier work and found spectacular properties: high toughness and strength, which are usually mutually exclusive in a material,” says Robert Ritchie, a scientist with Berkeley Lab’s Materials Sciences Division who led the research with Qian Yu of China’s Zhejiang University and several other scientists.

“So in this research, we used TEM to study the alloy at the nanoscale to see what’s going on,” says Ritchie.

In materials science, toughness is a material’s resistance to fracture, while strength is a material’s resistance to deformation. It’s very rare for a material to be both highly tough and strong, but CrMnFeCoNi isn’t a run-of-the-mill alloy. It’s a star member of a new class of alloys developed about a decade ago that contains five or more elements in roughly equal amounts. In contrast, most conventional alloys have one dominant element. These new multi-component alloys are called high-entropy alloys because they consist primarily of a simple solid solution phase, and therefore have a high entropy of mixing.

They’re a hot topic in materials research, and have only recently been available in a quality suitable for study. In 2014, Ritchie and colleagues found that at very cold temperatures, when CrMnFeCoNi deforms, a phenomenon called “twinning” occurs, in which adjacent crystalline regions form mirror arrangements of one another. Twinning likely plays a part in the alloy’s incredible toughness and strength. But twinning isn’t extensively found in the alloy at room temperature (except in the crack bridges), yet the alloy’s toughness and strength is still almost off the charts.

“If we don’t see twinning at room temperature, then what other mechanisms give the alloy these amazing properties?” asks Ritchie.

To find out, the scientists subjected the alloy to several straining experiments at room temperature, and used transmission electron microscopy to observe what happens.

Their time-lapse images revealed two phenomena related to shear stress: slow-moving perfect dislocations that give the material strength, and fast-moving partial dislocations that enhance ductility. They also saw a phenomenon involving partial dislocations called “three-dimensional stacking fault defects,” in which the 3-D arrangement of atoms in a region changes. These faults are big barriers to dislocation, like placing a stack of bricks in front of a growing fissure, and serve to harden the alloy.

The images also captured the nanoscale version of chewing a mouthful of toffee and having your teeth stick together: In some cases, tiny bridges deformed by twinning are generated across a crack, which help prevent the crack from growing wider.

“These bridges are common in reinforced ceramics and composites,” says Ritchie. “Our research found that all of these nanoscale mechanisms work together to give the alloy its toughness and strength.”

Berkeley Lab

New Material for Detecting Photons Captures More Quantum Information

Colorized micrograph of a NIST single-photon detector made of superconducting nanowires patterned on molybdenum silicide.

Photo Credit: Verma/NIST

Detecting individual particles of light just got a bit more precise—by 74 picoseconds to be exact—thanks to advances in materials by National Institute of Standards and Technology (NIST) researchers and their colleagues in fabricating superconducting nanowires.

Although 74 picoseconds may not sound like much—a picosecond is a trillionth of a second—it is a big deal in the quantum world, where light particles, or photons, can carry valuable information. In this case it means that much less “jitter,” or uncertainty in the arrival time of a photon. Less jitter means that photons can be spaced more closely together but still be correctly detected. This enables communications at a higher bit rate, with more information transmitted in the same period.  

Every little bit helps when trying to receive faint signals reliably. It helped, for example, in NIST’s recent quantum teleportation record and difficult tests of physics theories. In such experiments, researchers want to decode as much information as possible from the quantum properties of billions of photons, or determine if “entangled” photons have properties that are linked before—or only after—being measured.  

NIST has made many advances in photon detector designs. In the latest work, described inOptics Express, NIST researchers used an electron beam to pattern nanowires into a thin film made of a heat-tolerant ceramic superconductor, molybdenum silicide. The tiny boost in energy that occurs when a single photon hits is enough to make the nanowires briefly lose their superconducting capability and become normal conductors, signaling the event.  

Nanowire detectors are superfast, counting tens of millions of photons per second, and generating few “dark” (or false) counts. Originally they were inefficient—meaning they missed photons they should have counted—but NIST has been fine-tuning their properties, first by boosting efficiency and now reducing jitter.  

The new design improves on NIST’s 2011 tungsten-silicon alloy material because it can operate at higher (though still cryogenic) temperatures and at a higher electrical current. The higher temperature simplifies refrigeration; the higher current cuts jitter in half, from about 150 picoseconds to 76 picoseconds. NIST researchers enhanced the detector’s light absorption and efficiency by embedding the chip in a cavity made of gold mirrors and layers of other unreactive materials.  

Researchers demonstrated detector efficiencies of 87 percent at wavelengths that are useful in telecommunications. This was almost as efficient as tungsten-silicon devices (93 percent) but with significantly lower jitter.  

The molybdenum-silicide material adds to NIST’s contributions in the competitive international field of quantum information science. Development of next-generation sensors offering high precision is a NIST priority. NIST single-photon detectors are used in a variety of experiments around the world. 

The detectors were made in NIST Boulder’s microfabrication facility. Researchers from the University of Geneva in Switzerland and the Jet Propulsion Laboratory at the California Institute of Technology also contributed to the work. 

NIST

Graphene partnership could deliver next generation of aircraft

Graphene composite-based planes could be a step closer to reality as a result of a partnership between The University of Manchester and a leading Chinese aviation company.

 

Graphene composites could deliver the next generation of aeroplanes

Beijing Institute of Aeronautical Materials（BIAM）has become the latest partner of the National Graphene Institute (NGI), based at the University, to promote the research and development in graphene reinforced aluminium matrix composites areas, and accelerate the application of graphene in the aviation industry and other sectors.

The NGI has around 50 industrial partners working collaboratively on a range of potential applications. The Institute has a number of collaborations with Chinese companies, and in October hosted President Xi Jinping as part of his state visit to the UK.

For this project, BIAM and the University, under the leadership of Professor Robert Young, will exchange expertise and cooperate on the structural characterisation and property testing of graphene reinforced aluminium matrix nanocomposites. 

The projects could result in lighter, stronger and conductive parts for aeroplanes, high speed trains and other industrial equipment to replace traditional materials. With graphene added, the strength of aluminium alloy could be highly improved while retaining its ductile quality. 

The collaboration could improve the technology maturity and accelerate the updating of aeroplane structural materials and functional materials.

In the future, the two parties expect to expand the collaboration on graphene materials. Besides the graphene reinforced aluminium matrix composites, both parties will seek collaboration in areas of graphene energy storage materials, environmental purification materials and information materials.

Dai Shenglong, President of BIAM, said: “Graphene is expected to revolutionize the technology sector. Graphene and its products have unique properties and show wide prospects for applications. 

“BIAM has obtained achievements in the areas of graphene modified structural materials and functional materials, the preparation process and large scale production of graphene nanoflakes and graphene films, and has achieved some extensive application experiences in the aviation industry. 

“Now the collaboration with The University of Manchester will give full play to both sides’ favorable conditions, enhance fundamental research level, improve the technology maturity, and promote together the development of graphene and its products.”

James Baker, Business Director at The University of Manchester, said: “We are delighted to be working with BIAM on collaborative graphene applications.

“Aerospace and other transport areas show great potential for graphene activity and The University of Manchester is leading the way in these areas and many others. Partnering with companies like BIAM gives up the opportunity to accelerate products to market and turn fundamental research into applications of the future.” 

BIAM mainly focuses on the engineering application of graphene modified structural materials and functional materials, and the R&D of graphene related new products and exploitation. 

Manchester National Graphene Institute