Forța și ductilitatea aliajelor(Strength and ductility for alloys)

un nou tip de material metalic extrem de puternic, dar ductil.Materialele metalice din forjarea materialelor de la Düsseldorf ar putea fi prelucrate la fel de ușor și în mod rentabil ca oțelul ductil în mod special și vor absorbi cât mai multă energie de impact într-un accident atunci când sunt încorporate în caroseria unei mașini. În același timp, materialul ar fi suficient de puternic încât foile de metal subțiri și, deci, ieftine și care economisesc resursele, să nu renunțe când sunt supuse unei forțe slabe.

Posted: May 24, 2016
Strength and ductility for alloys (Nanowerk News) For the steel industry, there may be a way out of the dilemma that has existed since people began processing metal. Scientists from the Max-Planck-Institut für Eisenforschung in Düsseldorf (Germany) are presenting a new type of metallic material that is extremely strong, but simultaneously ductile.
Up until now, one material property could only be improved at the expense of the other – something that is being changed by the Düsseldorf-based researchers, who are entering new terrain in the development of metallic materials.
Their work (Nature, „Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off”) is thus contributing to the future design of metallic components with thinner sheets, and thereby helping to save resources.

A strong alloy made of iron, manganese, cobalt and chrome becomes ductile because it can have two coexisting crystal structures, and one structure can transform into the other. The two crystal structures can be identified by the two different colours in this cross section of the material, which was produced with the aid of electron backscatter diffraction.
Ideally, steels and steel-related alloys should be capable of both properties: they should not fragment, for example during processing in a mill or as car bodies involved in an accident. In other words, they must be “ductile”, as materials scientists refer to it. However, they also need to be strong so that they do not warp or break when subjected to weak forces. A team headed by Dierk Raabe, director at the Max-Planck-Institut für Eisenforschung, and Cemal Cem Tasan, formerly head of a research group at this Institute and now professor at the Massachusetts Institute of Technology in the US, has now succeeded in combining both properties in one material. To date, extremely ductile metallic materials were not particularly strong and vice versa.
“We pursued a new strategy in the development of this material, which generally opens up new possibilities for the design of metallic materials,” says Dierk Raabe.
The team began at a type of material that has been the subject of extensive testing by materials scientists in recent years, but which was too brittle for many applications up until now: alloys in which metallurgists combine similar quantities of typically five or more different metals.
Atomic disorder enables high-strength alloys
As the atoms of the different elements are distributed along the positions in the crystal lattices of these materials without any identifiable order and the entropy is, to a certain extent, a measure for the disorder, the materials are called high-entropy alloys. Such materials can be particularly strong because the disorder of the numerous different atoms in a structure makes it difficult for dislocations to move.
Dislocations are defects in the crystal lattice that move through a crystal when a material becomes deformed. However, there has been one disadvantage to the high strength of the alloys with atomic disorder till now: when such a material gives way under pressure, it is usually brittle.
Steels that mainly contain iron, usually another main component and small quantities of other elements like carbon, vanadium or chrome, are, on the other hand, often ductile. They are not brittle; however, up until now they have not been strong enough to enable, for example, the construction of car bodies with thinner sheets. In the crystals of steels, the atoms are more or less regularly arranged.
Steels become particularly ductile though if they can switch from one structure to another. This is because this process swallows energy, which can then no longer initiate any damage in the material. In a car body or other steel components, tiny areas then alternate with the two different atom arrangements.
The change in the crystal structure makes the material ductile
It was precisely this coexistence of the different crystal structures that was detrimental to the high-entropy alloys – thus far.
“We have now turned this conception on its head, as recent studies have shown that this is not the important factor,” says Zhiming Li, who made this scientific turnaround the topic of his project.
Together with his colleagues, Li searched for a material that is, on the one hand, as strong as a high-entropy alloy, but, like particularly ductile steels, has two coexisting crystal structures. The search produced an alloy made from 50 per cent iron, 30 per cent manganese and 10 per cent respectively of cobalt and chrome.
“With this alloy, we have shown that our concept works,” says Raabe. “If we further improve the microstructure and the composition, we can even further enhance the strength and ductility.”
This is precisely the area the researchers are now working on. This means that they could, once and for all, solve the metal-processing industry’s dilemma of having to choose between strong or ductile materials. The metallic materials from the Düsseldorf-based materials forge could be processed just as easily and cost-efficiently as a particularly ductile steel and absorb as much impact energy in an accident when incorporated in the body of a car. At the same time, the material would be strong enough that thin and thus low-cost and resource-conserving metal sheets do not give way when subjected to a weak force.

Source: Max-Planck-Institut für Eisenforschung

Oamenii de știință fac un salt major spre un metamaterial cuantic „perfect” ( Scientists take a major leap toward a ‘perfect’ quantum metamaterial )

au inventat o modalitate de a construi un „metamaterial cuantic” – un material fabricat cu proprietati exotice care nu se gasesc in natura folosind atomi ultracold prinsi intr-un cristal artificial compus din lumina.Cercetătorii au descoperit că atomii de rubidiu sunt ideali pentru acest studiu, totuși atomii de bariu, calciu și cesiu pot fi prinși sau plantați în cristalul artificial, deoarece prezintă niveluri similare de energie. În timp ce cristalul artificial utilizat în studiu este descris ca fiind unidimensional, Jha a spus că aceeași abordare ar putea fi ușor extinsă pentru a crea structuri cristaline metamateriale cuantice 2-D și 3-D din lumină.

Posted: May 11, 2016
Scientists take a major leap toward a ‘perfect’ quantum metamaterial (Nanowerk News) Scientists have devised a way to build a “quantum metamaterial”—an engineered material with exotic properties not found in nature—using ultracold atoms trapped in an artificial crystal composed of light. The theoretical work represents a step toward manipulating atoms to transmit information, perform complex simulations or function as powerful sensors.
The research team, led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, proposes the use of an accordion-like atomic framework, or “lattice” structure, made with laser light to trap atoms in regularly spaced nanoscale pockets. Such a light-based structure, which has patterned features that in some ways resemble those of a crystal, is essentially a “perfect” structure—free of the typical defects found in natural materials.
Researchers believe they can pinpoint the placement of a so-called “probe” atom in this crystal of light, and actively tune its behavior with another type of laser light (near-infrared light) to make the atom cough up some of its energy on demand in the form of a particle of light, or photon.
This photon, in turn, can be absorbed by another probe atom (in the same or different lattice site) in a simple form of information exchange—like spoken words traveling between two string-connected tin cans.

The wavelike pattern at the top shows the accordion-like structure of a proposed quantum material—an artificial crystal made of light—that can trap atoms in regularly spaced nanoscale pockets. These pockets can be made to hold a large collection of ultracold “host” atoms (green), slowed to a standstill by laser light, and individually planted “probe” atoms (red) that can be made to transmit quantum information in the form of a photon (particle of light). The lower panel shows how the artificial crystal can be reconfigured with light from an open (hyperbolic) geometry to a closed (elliptical) geometry, which greatly affects the speed at which the probe atom can release a photon.
“Our proposal is very significant,” said Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division who led the related research paper, published in April in Physical Review Letters („Coherence-Driven Topological Transition in Quantum Metamaterials”). “We know that the enhancement and ultrafast control of single-photon emission lies at the heart of quantum technologies, in particular quantum information processing, and this is exactly what we have achieved here. Previous proposals can do one or the other but not both simultaneously.”
Zhang is also a professor at UC Berkeley, director of the National Science Foundation’s Center for Scalable and Integrated Nanomanufacturing and a member of the Kavli Energy NanoScience Institute at Berkeley Lab and UC Berkeley.
Pankaj K. Jha, a UC Berkeley postdoctoral researcher who is the lead author of the paper and works in Zhang’s group, said, “Now we have control over the speed of the release of a photon, so we can optically process information much faster, and efficiently transfer it from one point to another.” Other scientists who contributed to this work include Michael Mrejen, Jeongmin Kim, Chihhui Wu, Yuan Wang and Yuri V. Rostovtsev.
This ability to release a photon at fast rates, and to transmit it with low losses from one atom to another, is a vital step in processing information for quantum computation, which could use an array of these controlled photon releases to carry out complex calculations far more rapidly than is possible in modern computers.
A quantum computer, which the tech industry and scientific community are hotly pursuing because of its potential to perform more complex calculations than are possible using modern supercomputers, could tap into the bizarre quantum realm in which ordinary physics rules don’t apply.
While today’s computers can store information as binary bits—either ones or zeroes—a quantum compter would use “qubits” in which an individual bit of information can simultaneously exist in multiple states. These qubits could take the form of atoms, photons, electrons, or even as an individual fundamental property of a particle, and would exponentially increase the number of calculations a computer could perform in an instant.
The non-uniform distribution of the ultracold atoms in the artificial crystal is a key to this latest study, said Jha. “It makes the crucial difference for creating a ‘perfectly’ lossless and reconfigurable quantum metamaterial,” he said, allowing the optical structure of the artificial crystal to be reconfigured from an open geometry (hyperbolic-shaped) to a closed one (elliptical) at the same frequency and with ultrafast timing. This controllable shape-change dramatically changes the speed at which a probe atom in the artificial crystal releases a photon.
The latest proposal suggests that it is possible to speed up the rate at which a probe atom can emit a photon from nanoseconds, or billionths of a second, to picoseconds, or trillionths of a second. Also, this process is importantly considered „lossless,” meaning the photons would not lose any of their energy to their surrounding structure as they likely would in a traditional material. This overcomes one hurdle toward quantum computing and information processing.
Atoms planted in the artificial crystal could also possibly be induced to hop from one place to another. In this case, the atoms could themselves serve as the information carriers in a quantum computer or be arranged as quantum sensors, Jha said.
Jha noted that this latest study marries metamaterials research with the science of “cold atoms,” which are atoms that have been slowed and even brought to a standstill using laser light, which in the process chills them to supercool temperatures. He said, “This integration has solved some of the outstanding challenges for metamaterial platforms and outperforms other designs in several key aspects crucial for quantum technologies.”
The researchers found that rubidium atoms are ideally suited for this study, however barium, calcium and cesium atoms can also be trapped or planted in the artificial crystal, as they exhibit similar energy levels. While the artificial crystal used in the study is described as one-dimensional, Jha said the same approach could be easily extended to create 2-D and 3-D quantum metamaterial crystal structures out of light.
To realize the proposed metamaterial in an actual experiment, Zhang and Jha said the research team would need to trap several atoms per lattice site in the artificial crystal, and to hold those atoms in the lattice even when they are excited to higher energy states.
Zhang said, “Berkeley Lab has been a leader in groundbreaking research in metamaterials, and this work could open new realms of opportunities for quantum light-matter interactions, with enticing applications in quantum information science.”
Jha added, “We believe that the combination of these two contemporary realms of science will help to address key challenges in both fields and open an entirely new research direction at the interface of quantum photonics and artificial materials.”

Source: Lawrence Berkeley National Laboratory

Cercetările noi arată că argintul ar putea fi cheia gadgeturilor flexibile din aur ( New research shows how silver could be the key to gold-standard flexible gadgets )

Materialele alternative investigate ca înlocuitori ITO au inclus grafen, nanotuburi de carbon și filme aleatoare de nanoparticule metalice. Acest studiu a arătat cum au apărut filmele de nanofire din argint ca fiind cel mai puternic concurent, datorită transmisiilor și conductivităților care se pot potrivi și depășesc ușor cele ale ITO. Acesta este un material care constă din fire care sunt de peste o mie de ori mai subțiri decât părul uman, care formează o rețea conductivă interconectată.

Posted: May 11, 2016
New research shows how silver could be the key to gold-standard flexible gadgets (Nanowerk News) Research published in the journals Materials Today Communications and Scientific Reports („Predicting the optoelectronic properties of nanowire films based on control of length polydispersity”) has described how silver nanowires are proving to be the ideal material for flexible, touch-screen technologies while also exploring how the material can be manipulated to tune its performance for other applications. Currently, touch screen devices mainly rely on electrodes made from indium tin oxide (ITO), a material that is expensive to source, expensive to process and very brittle.

Silver nanowires are an ideal material for current and future flexible touch-screen technologies.
A team from the University of Surrey, led by Professor Alan Dalton and in collaboration with M-SOLV Ltd, a touch-sensor manufacturer based in Oxford, looked to alternative materials to overcome the challenges of ITO, which is suffering from supply uncertainty. Alternative materials investigated as ITO replacements have included graphene, carbon nanotubes and random metal nanowire films. This study showed how silver nanowire films have emerged as the strongest competitor, due to transmittances and conductivities which can match and readily exceed those of ITO. This is a material that consists of wires which are over a thousand times thinner than a human hair, that form an interconnected conductive network.
Showcasing a new process
Matthew Large, the first author on the research published in Scientific Reports described the importance of these latest results. “Our research hasn’t just identified silver nanowires as a viable replacement touchscreen material, but has gone one step further in showing how a process called ‘ultrasonication’ can allow us to tailor performance capabilities. By applying high frequency sound energy to the material we can manipulate how long the nanosized ‘rods’ of silver are. This allows us to tune how transparent or how conductive our films are, which is vital for optimising these materials for future technologies like flexible solar cells and roll-able electronic displays.”
In a paper published last month in Materials Today Communications, the same team, showed how silver nanowires can be processed using the same laser ablation technique commonly used to manufacture ITO devices. Using this technique, the team produced a fully operating five inch multi-touch sensor, identical to those typically used in smartphone technology. They found it performed comparably to one based on ITO but used significantly less energy to produce.
“Not only does this flexible material perform very well, we have shown that it is a viable alternative to ITO in practical devices,” concluded Professor Dalton. “The fact we are able to produce devices using similar methods as currently in use, but in a less energy-intensive way is an exciting step towards flexible gadgets that do not just open the door for new applications, but do so in a much greener way.”
An easy to deploy alternative
Maria Cann, a technologist from M-SOLV and first author on the Materials Today Communications paper added ““We are seeing a lot of interest from our customers in silver nanowire films as an ITO replacement in devices. This work is a really important step in establishing exactly which sensor designs can make good nanowire products. The fact that the nanowire films are processed by the same laser techniques as ITO makes the transition from ITO to nanowires really straightforward. It won’t be long before we are all using nanowires in our electronic devices.”
The team, now based at the University of Sussex is now looking to develop the scalability of the process to make it more industrially viable. One limiting factor is the current cost of silver nanowires.

Source: University of Surrey

Oamenii de știință fac un salt major spre un metamaterial cuantic „perfect”(Scientists take a major leap toward a ‘perfect’ quantum metamaterial)

Oamenii de stiinta au inventat o modalitate de a construi un „metamaterial cuantic” – un material fabricat cu proprietati exotice care nu se gaseste in natura folosind atomi ultracold prinsi intr-un cristal artificial compus din lumina.Manipularea atomilor pentru a transmite informații, a efectua simulări complexe sau a funcționa ca senzori puternici.

Posted: May 11, 2016
Scientists take a major leap toward a ‘perfect’ quantum metamaterial (Nanowerk News) Scientists have devised a way to build a “quantum metamaterial”—an engineered material with exotic properties not found in nature—using ultracold atoms trapped in an artificial crystal composed of light. The theoretical work represents a step toward manipulating atoms to transmit information, perform complex simulations or function as powerful sensors.
The research team, led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, proposes the use of an accordion-like atomic framework, or “lattice” structure, made with laser light to trap atoms in regularly spaced nanoscale pockets. Such a light-based structure, which has patterned features that in some ways resemble those of a crystal, is essentially a “perfect” structure—free of the typical defects found in natural materials.
Researchers believe they can pinpoint the placement of a so-called “probe” atom in this crystal of light, and actively tune its behavior with another type of laser light (near-infrared light) to make the atom cough up some of its energy on demand in the form of a particle of light, or photon.
This photon, in turn, can be absorbed by another probe atom (in the same or different lattice site) in a simple form of information exchange—like spoken words traveling between two string-connected tin cans.

The wavelike pattern at the top shows the accordion-like structure of a proposed quantum material—an artificial crystal made of light—that can trap atoms in regularly spaced nanoscale pockets. These pockets can be made to hold a large collection of ultracold “host” atoms (green), slowed to a standstill by laser light, and individually planted “probe” atoms (red) that can be made to transmit quantum information in the form of a photon (particle of light). The lower panel shows how the artificial crystal can be reconfigured with light from an open (hyperbolic) geometry to a closed (elliptical) geometry, which greatly affects the speed at which the probe atom can release a photon.
“Our proposal is very significant,” said Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division who led the related research paper, published in April in Physical Review Letters(„Coherence-Driven Topological Transition in Quantum Metamaterials”). “We know that the enhancement and ultrafast control of single-photon emission lies at the heart of quantum technologies, in particular quantum information processing, and this is exactly what we have achieved here. Previous proposals can do one or the other but not both simultaneously.”
Zhang is also a professor at UC Berkeley, director of the National Science Foundation’s Center for Scalable and Integrated Nanomanufacturing and a member of the Kavli Energy NanoScience Institute at Berkeley Lab and UC Berkeley.
Pankaj K. Jha, a UC Berkeley postdoctoral researcher who is the lead author of the paper and works in Zhang’s group, said, “Now we have control over the speed of the release of a photon, so we can optically process information much faster, and efficiently transfer it from one point to another.” Other scientists who contributed to this work include Michael Mrejen, Jeongmin Kim, Chihhui Wu, Yuan Wang and Yuri V. Rostovtsev.
This ability to release a photon at fast rates, and to transmit it with low losses from one atom to another, is a vital step in processing information for quantum computation, which could use an array of these controlled photon releases to carry out complex calculations far more rapidly than is possible in modern computers.
A quantum computer, which the tech industry and scientific community are hotly pursuing because of its potential to perform more complex calculations than are possible using modern supercomputers, could tap into the bizarre quantum realm in which ordinary physics rules don’t apply.
While today’s computers can store information as binary bits—either ones or zeroes—a quantum compter would use “qubits” in which an individual bit of information can simultaneously exist in multiple states. These qubits could take the form of atoms, photons, electrons, or even as an individual fundamental property of a particle, and would exponentially increase the number of calculations a computer could perform in an instant.
The non-uniform distribution of the ultracold atoms in the artificial crystal is a key to this latest study, said Jha. “It makes the crucial difference for creating a ‘perfectly’ lossless and reconfigurable quantum metamaterial,” he said, allowing the optical structure of the artificial crystal to be reconfigured from an open geometry (hyperbolic-shaped) to a closed one (elliptical) at the same frequency and with ultrafast timing. This controllable shape-change dramatically changes the speed at which a probe atom in the artificial crystal releases a photon.
The latest proposal suggests that it is possible to speed up the rate at which a probe atom can emit a photon from nanoseconds, or billionths of a second, to picoseconds, or trillionths of a second. Also, this process is importantly considered „lossless,” meaning the photons would not lose any of their energy to their surrounding structure as they likely would in a traditional material. This overcomes one hurdle toward quantum computing and information processing.
Atoms planted in the artificial crystal could also possibly be induced to hop from one place to another. In this case, the atoms could themselves serve as the information carriers in a quantum computer or be arranged as quantum sensors, Jha said.
Jha noted that this latest study marries metamaterials research with the science of “cold atoms,” which are atoms that have been slowed and even brought to a standstill using laser light, which in the process chills them to supercool temperatures. He said, “This integration has solved some of the outstanding challenges for metamaterial platforms and outperforms other designs in several key aspects crucial for quantum technologies.”
The researchers found that rubidium atoms are ideally suited for this study, however barium, calcium and cesium atoms can also be trapped or planted in the artificial crystal, as they exhibit similar energy levels. While the artificial crystal used in the study is described as one-dimensional, Jha said the same approach could be easily extended to create 2-D and 3-D quantum metamaterial crystal structures out of light.
To realize the proposed metamaterial in an actual experiment, Zhang and Jha said the research team would need to trap several atoms per lattice site in the artificial crystal, and to hold those atoms in the lattice even when they are excited to higher energy states.
Zhang said, “Berkeley Lab has been a leader in groundbreaking research in metamaterials, and this work could open new realms of opportunities for quantum light-matter interactions, with enticing applications in quantum information science.”
Jha added, “We believe that the combination of these two contemporary realms of science will help to address key challenges in both fields and open an entirely new research direction at the interface of quantum photonics and artificial materials.”

Source: Lawrence Berkeley National Laboratory

Noul design de celule de combustie alimentat de nanocristale învelite în grafen (New fuel cell design powered by graphene-wrapped nanocrystals)

au elaborat o rețetă de materiale noi pentru o baterie Hidrogenul de combustibil – care înconjoară nanocristalele de magneziu absorbante de hidrogen cu foi grafenice atomice subțiri – pentru a-și împinge performanțele înainte în zonele cheie.Aceste cristale de magneziu încapsulate cu grafeni acționează ca „bureți” pentru hidrogen, oferind o modalitate foarte compactă și sigură de a lua și de a stoca hidrogen. Nanocristalele permit, de asemenea, o alimentare mai rapidă și reduce dimensiunea totală a rezervorului.

Posted: Mar 11, 2016

New fuel cell design powered by graphene-wrapped nanocrystals

(Nanowerk News) Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn’t be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers–with water as the only byproduct of combustion.While there remain scientific challenges to making hydrogen-based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like hydrogen fuel cell–which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets–to push its performance forward in key areas.The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for hydrogen storage. Illustration of Graphene Sheets and Magnesium Nanocrystal Thin sheets of graphene oxide (red sheets) have natural, atomic-scale defects that allow hydrogen gas molecules to pass through while blocking larger molecules such as oxygen (O2) and water (H2O). Berkeley Lab researchers encapsulated nanoscale magnesium crystals (yellow) with graphene oxide sheets to produce a new formula for metal hydride fuel cells. (Image: Jeong Yun Kim)These graphene-encapsulated magnesium crystals act as „sponges” for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall „tank” size.”Among metal hydride-based materials for hydrogen storage for fuel-cell vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability,” said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications („Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage”).In a hydrogen fuel cell-powered vehicle using these materials, known as a „metal hydride” (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.Jeff Urban, a Berkeley Lab staff scientist and co-author, said, „This work suggests the possibility of practical hydrogen storage and use in the future. I believe that these materials represent a generally applicable approach to stabilizing reactive materials while still harnessing their unique activity–concepts that could have wide-ranging applications for batteries, catalysis, and energetic materials.”The research, conducted at Berkeley Lab’s Molecular Foundry and Advanced Light Source, is part of a National Lab Consortium, dubbed HyMARC (Hydrogen Materials–Advanced Research Consortium) that seeks safer and more cost-effective hydrogen storage, and Urban is Berkeley Lab’s lead scientist for that effort.The U.S. market share for all electric-drive vehicles in 2015, including full-electric, hybrids and plug-in hybrid vehicles, was 2.87 percent, which amounts to about 500,000 electric-drive vehicles out of total vehicle sales of about 17.4 million, according to statistics reported by the Electric Drive Transportation Association, a trade association promoting electric-drive vehicles.Hydrogen-fuel-cell vehicles haven’t yet made major in-roads in vehicle sales, though several major auto manufacturers including Toyota, Honda, and General Motors, have invested in developing hydrogen fuel-cell vehicles. Indeed, Toyota released a small-production model called the Mirai, which uses compressed-hydrogen tanks, last year in the U.S.A potential advantage for hydrogen-fuel-cell vehicles, in addition to their reduced environmental impact over standard-fuel vehicles, is the high specific energy of hydrogen, which means that hydrogen fuel cells can potentially take up less weight than other battery systems and fuel sources while yielding more electrical energy.A measure of the energy storage capacity per weight of hydrogen fuel cells, known as the „gravimetric energy density,” is roughly three times that of gasoline. Urban noted that this important property, if effectively used, could extend the total vehicle range of hydrogen-based transportation, and extend the time between refueling for many other applications, too.More R&D is needed to realize higher-capacity hydrogen storage for long-range vehicle applications that exceed the performance of existing electric-vehicle batteries, Cho said, and other applications may be better suited for hydrogen fuel cells in the short term, such as stationary power sources, forklifts and airport vehicles, portable power sources like laptop battery chargers, portable lighting, water and sewage pumps and emergency services equipment.Cho said that a roadblock to metal hydride storage has been a relatively slow rate in taking in (absorption) and giving out (desorption) hydrogen during the cycling of the units. In fuel cells, separate chemical reactions involving hydrogen and oxygen produce a flow of electrons that are channeled as electric current, creating water as a byproduct.The tiny size of the graphene-encapsulated nanocrystals created at Berkeley Lab, which measure only about 3-4 nanometers, or billionths of a meter across, is a key in the new fuel cell materials’ fast capture and release of hydrogen, Cho said, as they have more surface area available for reactions than the same material would at larger sizes.Another key is protecting the magnesium from exposure to air, which would render it unusable for the fuel cell, she added.Working at The Molecular Foundry, researchers found a simple, scalable and cost-effective „one pan” technique to mix up the graphene sheets and magnesium oxide nanocrystals in the same batch. They later studied the coated nanocrystals’ structure using X-rays at Berkeley Lab’s Advanced Light Source. The X-ray studies showed how hydrogen gas pumped into the fuel cell mixture reacted with the magnesium nanocrystals to form a more stable molecule called magnesium hydride while locking out oxygen from reaching the magnesium.”It is stable in air, which is important,” Cho said.Next steps in the research will focus on using different types of catalysts–which can improve the speed and efficiency of chemical reactions–to further improve the fuel cell’s conversion of electrical current, and in studying whether different types of material can also improve the fuel cell’s overall capacity, Cho said.
Source: Lawrence Berkeley National Laboratory
Read more: New fuel cell design powered by graphene-wrapped nanocrystals

Nano-materiale noi funcționalizate pentru captarea dioxidului de carbon ( Novel functionalized nanomaterials for carbon dioxide capture )

au creat noi nanomateriale funcționale care permit o încărcare mai mare a aminei, cu o scădere minimă a suprafeței.Nanosilice nostru fibros (KCC-1) ar trebui să fie un bun candidat pentru a fi utilizat ca suport pentru a proiecta eficient de CO 2 sorbenți , care ar permite o mai bună capacitate de captare, cinetică și recylability“, spune Dr. Vivek Polshettiwar, stiinta de plumb al acestui studiu. O caracteristică unică a KCC-1 este suprafața sa mare, care provine din morfologia sa fibroasă și nu din canalele sale mezoporoase (spre deosebire de alte materiale bine studiate cum ar fi SBA-15 sau MCM-41).

Posted: May 09, 2016
Novel functionalized nanomaterials for carbon dioxide capture (Nanowerk News) Climate change due to excessive CO2 levels is one of the most serious problems mankind has ever faced. This has resulted in abrupt weather patterns such as flood and drought, which are extremely disruptive and detrimental to life, as we have been witnessing in India in recent years. Mitigating rising CO2 levels is of prime importance. In a new development, scientists at the Tata Institute of Fundamental Research, Mumbai, have developed a novel design of CO2 sorbents that show superior CO2 capture capacity and stability over conventional materials.
The immobilization of functional amines on a porous solid support can result in stable and efficient CO2 sorbent materials compared to similar liquid sorbents. A critical disadvantage however, is a drastic decrease in the textural properties of these supports (i.e., their surface area and pore volume), leading to a decrease in the CO2 capture capability.
To overcome this challenge, scientists at TIFR Mumbai, have designed novel functionalised nanomaterials that allows higher amine loading with a minimal decrease in surface area.
2 Capture” border=”0″ align=”middle”>
Novel functionalized nanomaterials for CO2 capture. (© RSC)
„Our fibrous nanosilica (KCC-1) should be a good candidate for use as a support to design efficient CO2 sorbents that would allow better capture capacity, kinetics and recylability”, says Dr Vivek Polshettiwar, the lead scientist of this study. A unique feature of KCC-1 is its high surface area, which originates from its fibrous morphology and not from its mesoporous channels (unlike in other well studied materials like SBA-15 or MCM-41).
This study, published recently in the Journal of Materials Chemistry A („Design of CO2 sorbents using functionalized fibrous nanosilica (KCC-1): insights into the effect of the silica morphology (KCC-1 vs. MCM-41)”), demonstrates the usefulness of the fibrous morphology of KCC-1 compared to conventional ordered mesoporous silica. This work is in continuation of the teams efforts to develop sustainable catalysts and sorbents.
The KCC-1-based sorbents showed several advantages over conventional silica-based sorbents, including i) high amine loading, ii) minimum reduction in surface area after functionalization and iii) more accessibility of the amine sites to enhance CO2 capture efficiency (i.e., capture capacity, kinetics and recyclability), due to the fibrous structure and high accessible surface area of KCC-1.
The demand for such efficient sorbents is on the rise since CO2 capture is one of the best solutions to mitigate the rising levels of CO2. Solid sorbents exhibit better efficiency with greater potential to overcome the shortcomings of liquid sorbents.
The use of mesoporous silica materials functionalized with various amino groups is well reported. Although materials like SBA-15 and MCM-41, for example, have attracted significant attention because their large pore sizes can accommodate a variety of amine molecules and the high surface area allows for a higher loading of these functional molecules, they suffer from the disadvantages of a decrease in textural properties, thus making KCC-1 a suitable candidate for more efficient CO2 capture.

Source: Tata Institute of Fundamental Research

Schimbarea culorii fotonilor unici într-o memorie cuantică de diamante (Changing the color of single photons in a diamond quantum memory)

au transformat pentru prima data culoarea si lățimea de banda a fotonilor ultra-rapizi folosind o memorie cuantica la temperatura camerei diamant.
Schimbarea culorii unui foton sau schimbarea frecvenței acestuia este necesară pentru a conecta în mod optim componentele dintr-o rețea cuantică. De exemplu, în comunicarea cuantică optică, cea mai bună transmisie printr-o fibră optică este apropiată de infraroșu, dar mulți dintre senzorii care le măsoară funcționează mult mai bine pentru lumina vizibilă, care este o frecvență mai mare. Posibilitatea de a schimba culoarea fotonului între fibră și senzor permite o funcționare mai performantă, inclusiv rate mai mari ale datelor.

Posted: Apr 05, 2016
Changing the color of single photons in a diamond quantum memory (Nanowerk News) Researchers from the Institute for Quantum Computing at the University of Waterloo and the National Research Council of Canada (NRC) have, for the first time, converted the colour and bandwidth of ultrafast single photons using a room-temperature quantum memory in diamond.
Shifting the colour of a photon, or changing its frequency, is necessary to optimally link components in a quantum network. For example, in optical quantum communication, the best transmission through an optical fibre is near infrared, but many of the sensors that measure them work much better for visible light, which is a higher frequency. Being able to shift the colour of the photon between the fibre and the sensor enables higher performance operation, including bigger data rates.

This is an artist’s impression of quantum frequency conversion in a diamond quantum memory. Researchers from the Institute for Quantum Computing at the University of Waterloo and the National Research Council of Canada (NRC) have, for the first time, converted the colour and bandwidth of ultrafast single photons using a room-temperature quantum memory in diamond. (Image: Dr. Khabat Heshami, National Research Council Canada)
The research, published in Nature Communications („Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory”), demonstrated small frequency shifts that are useful for a communication protocol known as wavelength division multiplexing. This is used today when a sender needs to transmit large amounts of information through a transmission so the signal is broken into smaller packets of slightly different frequencies and sent through together. The information is then organized at the other end based on those frequencies.
In the experiments conducted at NRC, the researchers demonstrated the conversion of both the frequency and bandwidth of single photons using a room-temperature diamond quantum memory.
„Originally there was this thought that you just stop the photon, store it for a little while and get it back out. The fact that we can manipulate it at the same time is exciting,” said Kent Fisher a PhD student at the Institute for Quantum Computing and with the Department of Physics and Astronomy at Waterloo. „These findings could open the door for other uses of quantum memory as well.”
The diamond quantum memory works by converting the photon into a particular vibration of the carbon atoms in the diamond, called a phonon. This conversion works for many different colours of light allowing for the manipulation of a broad spectrum of light. The energy structure of diamond allows for this to occur at room temperature with very low noise. Researchers used strong laser pulses to store and retrieve the photon. By controlling the colours of these laser pulses, researchers controlled the colour of the retrieved photon.
„The fragility of quantum systems means that you are always working against the clock,” remarked Duncan England, researcher at NRC. „The interesting step that we’ve shown here is that by using extremely short pulses of light, we are able to beat the clock and maintain quantum performance.”
The integrated platform for photon storage and spectral conversion could be used for frequency multiplexing in quantum communication, as well as build up a very large entangled state – something called a cluster state. Researchers are interested in exploiting cluster states as the resource for quantum computing driven entirely by measurements.
„Canada is a power-house in quantum research and technology. This work is another example of what partners across the country can achieve when leveraging their joint expertise to build next-generation technologies,” noted Ben Sussman, program leader for NRC’s Quantum Photonics program.

Source: University of Waterloo

Explorarea fosforului, un material nou promitator

În cercetarea lor, care apare în ACS Nano Letters („anizotropică Electron-foton si Electron-fonon Interactions in Black Fosfor“), echipa a stabilit initial pentru a rafina o tehnică existentă pentru minerit determinist orientarea cristalului. Această tehnică, care profită de spectroscopie Raman, foloseste un laser pentru măsurarea vibrațiilor atomului în cristal ca energia se mișcă prin ea, cauzate de interacțiunea electron-fononice. Ca și alte interacțiuni, interacțiunile electron-fononice în interiorul cristalelor de atom-gros de fosfor negru sunt anizotrope și, odată măsurate, au fost folosite pentru a prezice orientarea cristalului.

Posted: Apr 29, 2016
Exploring phosphorene, a promising new material (Nanowerk News) Two-dimensional phosphane, a material known as phosphorene, has potential application as a material for semiconducting transistors in ever faster and more powerful computers. But there’s a hitch. Many of the useful properties of this material, like its ability to conduct electrons, are anisotropic, meaning they vary depending on the orientation of the crystal.
Now, a team including researchers at Rensselaer Polytechnic Institute (RPI) has developed a new method to quickly and accurately determine that orientation using the interactions between light and electrons within phosphorene and other atoms-thick crystals of black phosphorus. Phosphorene–a single layer of phosphorous atoms–was isolated for the first time in 2014, allowing physicists to begin exploring its properties experimentally and theoretically. Vincent Meunier, head of the Rensselaer Department of Physics, Applied Physics, and Astronomy and a leader of the team that developed the new method, published his first paper on the material–confirming the structure of phosphorene–in that same year.

Phosphorene. (Image: Matthew Cherny)
„This is a really interesting material because, depending on which direction you do things, you have completely different properties,” said Meunier, a member of the Rensselaer Center for Materials, Devices, and Integrated Systems (cMDIS). „But because it’s such a new material, it’s essential that we begin to understand and predict its intrinsic properties.”
Meunier and researchers at Rensselaer contributed to the theoretical modeling and prediction of the properties of phosphorene, drawing on the Rensselaer supercomputer, the Center for Computational Innovations (CCI), to perform calculations. Through the Rensselaer cMDIS, Meunier and his team are able to develop the potential of new materials such as phosphorene to serve in future generations of computers and other devices. Meunier’s research exemplifies the work being done at The New Polytechnic, addressing difficult and complex global challenges, the need for interdisciplinary and true collaboration, and the use of the latest tools and technologies, many of which are developed at Rensselaer.
In their research, which appears in ACS Nano Letters („Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus”), the team initially set out to refine an existing technique for determining the orientation of the crystal. This technique, which takes advantage of Raman spectroscopy, uses a laser to measure vibrations of the atoms within the crystal as energy moves through it, caused by electron-phonon interactions. Like other interactions, electron-phonon interactions within atoms-thick crystals of black phosphorus are anisotropic and, once measured, have been used to predict the orientation of the crystal.
In reviewing their initial results from Raman spectroscopy, the team noticed several inconsistencies. To investigate further, they obtained actual images of the orientation of their sample crystals using Transmission Electron Microscopy (TEM), and then compared them with the Raman spectroscopy results. As a topographic technique, TEM offers a definitive determination of the orientation of the crystal, but isn’t as easy to obtain as the Raman results. The comparison revealed that electron-phonon interactions alone did not accurately predict the orientation of the crystal. And the reason why led the way to yet another anisotropy of phosphorene–that of interactions between photons of light and electrons in the crystal.
„In Raman you use a laser to impart energy into the material, and it starts to vibrate in ways that are intrinsic to the material, and which, in phosphorene, are anisotropic,” said Meunier. „But it turns out that if you shine the light in different directions, you get different results, because the interaction between the light and the electrons in the material–the electron-photon interaction–is also anisotropic, but in a non-commensurate way.”
Meunier said the team had reason to believe phosphorene was anisotropic with respect to electron-photon interactions, but didn’t anticipate the importance of the property.
„Usually electron-photon anisotropy doesn’t make such a big difference, but here, because we have such a particular chemistry on the surface and such a strong anisotropy, it’s one of those materials where it makes a huge difference,” Meunier said.
Although the discovery revealed a flaw in the interpretations of Raman spectra relying on electron-phonon interactions, it also revealed that electron-photon interactions alone provide an accurate determination of the orientation of the crystal.
„It turns out that it’s not so easy to use Raman vibrations to find out the direction of the crystal,” Meunier said. „But, and this is the beautiful thing, what we found is that the electron-photon interaction (which can be measured by recording the amount of light absorbed)–the interaction between the electrons and the laser–is a good predictor of the direction. Now you can really predict how the material will behave as a function of excitement with an outside stimulus.”

Source: Rensselaer Polytechnic Institute

Oamenii de stiinta prezic o noua familie de materiale promitatoare pentru racirea in stare solida

Fizicienii Daniel Errandonea, al Institutului UV de Știința Materialelor (ICMUV), și Claudio Cazorla, de la Scoala de Stiinta si Ingineria Materialelor, Universitatea din New South Wales (Australia), tocmai au prezis făcut ion de materiale care efectuează: cum ar fi fluorină (CaF2) ar putea prezenta un efect mai mare mecano-caloric decât chiar grupul feroelectrice. În această lumină, conductorii de ioni apar ca o nouă familie de materiale cu aplicații promițătoare în răcire în stare solidă. Și vestea bună este, a făcut fluorita este foarte abundent în natură, cu depozite în multe țări, inclusiv Spania.
Mai în detaliu, studiul stabilește relația dintre tensiunea mecanică externă și de transport ionic în conductoarele de ioni utilizând dinamica moleculară (o metodă de simulare pe computer pentru studierea mișcărilor fizice ale atomilor și moleculelor) și calculele mecanicii cuantice.

Posted: Apr 29, 2016
Scientists predict promising new family of materials for solid-state cooling (Nanowerk News) In a new paper published in Nano Letters („Giant Mechanocaloric Effects in Fluorite-Structured Superionic Materials”), scientists from the University of Valencia point to a new family of materials with promising applications in solid-state cooling.
Scientists have long been using solid-state cooling methods as an alternative to conventional refrigeration techniques that rely on pollutant gases. However, the efficiency of solid-state cooling has typically left much to be desired, being up to four times less efficient than conventional methods. Until now the required mechano-caloric effects have only been observed in ferroelectric materials and superelastic metal alloys, both of which are very scarce and very costly.
But the search for more efficient materials might be over. Physicists Daniel Errandonea, of the UV’s Institute of Material Science (ICMUV), and Claudio Cazorla, of the School of Materials Science and Engineering, University of New South Wales (Australia), have just predicted that ion conducting materials such as fluorite (CaF2) might present a greater mechano-caloric effect than even the ferroelectric group. In this light, ion conductors emerge as a new family of materials with promising applications in solid-state cooling. And the good news is, that fluorite is very abundant in nature, with deposits in many countries including Spain.
In more detail, the study establishes the relationship between external mechanical tension and ionic transport in ion conductors using molecular dynamics (a computer simulation method for studying the physical movements of atoms and molecules) and quantum mechanics calculations.
The work shows that applying pressure to the material serves as an efficient means of adjusting critical temperature in superionic compounds (fast ion conductors).
These results, published in Nanoletters in April 2016, pave the way for a rational design of green cooling technologies that are not only more ecological, but more efficient and cost-effective than conventional cooling methods. They also have important implications for the development of solid-state batteries.

Source: RUVID

Ce este un lichid cu spin quant?

Caracterul evaziv lichide cuantice spin, face foarte dificil de a confirma existența lor și să identifice natura exactă a acestora. Prezența unui lichid cuantic de spin poate fi dedusă dintr-o lipsă de aliniere a rotirilor de electroni, dar confirmarea finală este complicat: absența probelor nu constituie o dovadă a absenței, deoarece zicale. O abordare mai sofisticată este de a descoperi mai multe caracteristici distinctive și unice ale lichidului cuantic de spin pentru a permite o confirmare pozitivă

Posted: Apr 29, 2016
What is a quantum spin liquid? (Nanowerk News) Magnetism is one of the oldest recognised material properties. Known since antiquity, records from the 3rd century BC describe how lodestone, a naturally occurring magnetised ore of iron, was used in primitive magnetic compasses. Today, thanks to the theory of quantum mechanics we now understand the nature of magnetism, too, with the concept of spin explaining the behaviour of elementary particles such as electrons in the material that make it magnetic.
Spin, a property of sub-atomic particles such as electrons and quarks, makes each individual electron behave as if it were a tiny magnetic compass needle. The millions or billions of electron spins in a piece of material interact with each other in various ways and stabilise to form the different possible magnetic states found in solid matter. Taken together in such large numbers, the spin of the material’s electrons grants the same magnetic properties to the material itself.
Magnetism is essential for the basic trappings of modernity: magnetic materials form the basis of modern electronics and information storage. With this in mind, scientists have pursued the discovery of materials with entirely new magnetic behaviours or new states of matter with unprecedented and potentially beneficial properties.
One is that of a quantum spin liquid (New Journal of Physics, „Focus on Quantum Spin Liquids”), first proposed by the Nobel Prize-winning theoretical physicist PW Anderson in the early 1970s. In a paper published in the journal Nature Materials („Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet”), a research team led by Professor Stephen Nagler at the Oak Ridge National Laboratory in the US has demonstrated the quantum spin liquid nature of the magnetic material ruthenium trichloride (α-RuCl3).
How do quantum spin liquids form?
Quantum spin liquids are frequently found in a class of materials known as frustrated magnets. In a conventional magnet, the interactions between spins result in stable formations, known as their long-range order, in which the magnetic directions of each individual electron is aligned.
Herbertsmithite, a candidate quantum spin liquid source. (Image: Rob Lavinsky/iRocks.com, CC BY-SA)In a frustrated magnet, the arrangement of electron spins prevents them from forming an ordered alignment, and so they collapse into a fluctuating, liquid-like state. In a true quantum spin liquid, the electron spins never align, and continue to fluctuate even at the very lowest temperatures of absolute zero, at which the spins in other magnetic states of matter would have already frozen.The conditions required for a quantum spin liquid to form are often found in nature. The most famous example is the copper-based mineral Herbertsmithite, for which there is significant evidence to suggest that a quantum spin liquid state exists within the frustrated magnetic layers of copper ions that make up its structure. Where do we find quantum spin liquids? A challenge for scientists is to recreate the conditions required to synthetically grow candidate quantum spin liquid materials in the laboratory to allow for a complete understanding of their properties.
Quantum spin liquids’ evasive character make it notoriously difficult to confirm their existence and pinpoint their exact nature. The presence of a quantum spin liquid can be inferred from a lack of alignment of electron spins, but definitive confirmation is tricky: absence of evidence is not evidence of absence, as the adage goes. A more sophisticated approach is to uncover the more distinctive and unique characteristics of the quantum spin liquid to allow for a positive confirmation.
This is why Nagler’s study is particularly noteworthy. In experiments using neutron spectroscopy, the team revealed that α-RuCl3 realises something extremely close to a special flavour of quantum spin liquid called a Kitaev spin liquid. A prerequisite for this particular quantum spin liquid state is that the spins of the magnetic ruthenium ions form a frustrated honeycomb network: a layered, two-dimensional hexagonal structure, similar to that assumed by carbon atoms in graphite.
In their experiment, a beam of neutron particles created by a particle accelerator was scattered from the sample of α-RuCl3 transferring energy between the neutrons and the sample in the process. This energy transfer was quantified by a set of detectors surrounding the sample, and the response observed fits that described by the theory developed for the Kitaev quantum spin liquid in particular.
What can we do with quantum spin liquids?
We now recognise that the quantum spin liquid comes in several different varieties with subtly different properties, but that they all share the ability to support peculiar quantum mechanical phenomena. This is exciting, and not just from a purely scientific perspective: these states could be used in the development of quantum computers and other transformative quantum technologies that are expected to provide revolutionary changes to how we process and store data throughout the 21st century.
In the age of quantum computing, we will be able to perform calculations that are currently unsolvable on even the most powerful supercomputers of today. This will allow for breakthroughs in a vast array of fields in which we are tackling some of the biggest challenges of our time, from drug discovery to the design of smarter materials for a whole host of applications. As we discover more candidate quantum state liquid materials and better understand their behaviour, we will unravel ever more exotic physics and discover ways to manipulate and control this novel state of matter to our advantage.

Source: By Lucy Clark, Research Fellow, University of St Andrews, via The Conversation

Curenții oscilanți indică aplicarea practică a izolatoarelor topologice(Oscillating currents point to practical application for topological insulators)

În condițiile corecte, materialul, un compus numit hexaborid de samarium, este un izolator topologic – ceva care conduce electricitatea pe suprafața sa, dar nu prin interiorul său. Primele exemple de izolatoare topologice au fost create recent în laborator, iar descoperirea lor a dat naștere unui mare interes teoretic și experimental.

Posted: Apr 22, 2016
Oscillating currents point to practical application for topological insulators (Nanowerk News) Scientists studying an exotic material have found a potential application for its unusual properties, a discovery that could improve devices found in most digital electronics.
Under the right conditions the material, a compound called samarium hexaboride, is a topological insulator—something that conducts electricity on its surface but not through its interior. The first examples of topological insulators were only recently created in the lab, and their discovery has sparked a great deal of theoretical and experimental interest.
Now, a team of physicists at JQI and the University of California, Irvine, may have found a use for tiny crystals of samarium hexaboride. When pumped with a small but constant electric current and cooled to near absolute zero, the crystals can produce a current that oscillates. The frequency of that oscillation can be tuned by changing the amount of pump current or the crystal size.

A scanning electron microscope picture of platinum wires on a samarium hexaboride crystal, which can produce an electric current that flips millions of times a second. (Image: A. Stern/UCI)
This behavior—which mimics that of components in modern cell phones and computers in a much smaller package—is due to a complex interaction between currents carried by protected electronic states on the crystal’s surface and the temperature changes they provoke in the crystal’s interior.
„It’s not often that devices rely on such sophisticated ingredients,” says JQI Fellow Victor Galitski, who partnered with Dmitry Efimkin, a postdoctoral researcher in the Condensed Matter Theory Center at the University of Maryland, as well as experimentalists at UCI on the new work. Galitski and his colleagues published the results April 20 in Physical Review Letters („Radio Frequency Tunable Oscillator Device Based on a SmB6 Microcrystal”).
The work is the latest development in more than four decades of research on samarium hexaboride (link is external), which is known for its unusual properties at low temperatures. At high temperatures, the material acts like an ordinary metal, but as it is cooled down, its resistance to electrical currents increases. Unlike most materials, however, the resistance doesn’t keep increasing. Rather, it plateaus, even as the temperature continues to drop.
In 2010, Galitski and several colleagues hypothesized that this mysterious behavior arose because samarium hexaboride is a particular kind of material, which they dubbed a topological Kondo insulator. They predicted that such a material would exhibit a transition from a conventional metal at high temperatures to a topological insulator when cooled down. Physicists raced to verify the prediction by trying to observe signature surface currents. Along the way a group at UCI noticed that the material could also produce an oscillating current („Limit Cycle and Anomalous Capacitance in the Kondo Insulator SmB6„).
„That was a completely accidental discovery,” says Jing Xia, an associate professor of physics at the University of California, Irvine, and a co-author of the new paper. „We had no clue what was going on.”
The frequency of those early oscillating currents was too low to be useful in modern devices, so Xia and Galitski began parallel investigations, with Xia trying to scale down the crystal size to create faster oscillations and Galitski trying to explain the origin of the fluctuating current.
The new paper is the culmination of their efforts. The crystals are now much smaller—just 100 microns long compared to sizes of millimeters in the previous work. This leads to current oscillations that occur tens of millions of times a second, frequencies which can drive radio transmitters or the clocks found in computer chips.
The small size also created headaches for Alex Stern, a graduate student at UCI and lead author of the paper, who painstakingly connected miniscule platinum wires to the tiny crystals in order to make the measurements. „It was really just getting lucky after doing it several times,” Stern says. „And once you get one wire on, the hardest thing was to get the second one on right next to it.”
Meanwhile, Galitski and Efimkin worked on developing a model to explain the origin of the current oscillations. In the paper, the researchers derive equations that describe how current-carrying charges are transported through the material. Depending on experimental parameters, the charges either flow steadily or fluctuate, the latter corresponding to an oscillating current. Those oscillations appear for only a narrow range of parameters, and the researchers say they were lucky that their sample fall into this regime.

Despite the technical complexity of the theory, Galitski says that the physical mechanism that drives these fluctuations is simple. The essential steps are shown in the graphic above. As a current begins to flow on the crystal’s surface, a high resistance causes some of the current’s energy to heat the sample’s interior. This causes the electrical resistance of the interior to decrease slightly, momentarily allowing more current to flow. But the decreased resistance also dissipates less energy, so the interior cools back down and the original resistance is restored. This process repeats itself many times a second to produce the fluctuating current seen in experiments.
The authors suspect that smaller crystals could produce even faster oscillations, on the order of a trillion per second. The team says that this might happen for crystals that are 10 times smaller than the 100-micron long crystals they are using now. They add that there is no fundamental reason that similar devices that support rapid oscillations cannot be engineered to operate at room temperature.

Source: Joint Quantum Institute

Strength and ductility for alloys

Scientists take a major leap toward a ‘perfect’ quantum metamaterial

New research shows how silver could be the key to gold-standard flexible gadgets

Scientists take a major leap toward a ‘perfect’ quantum metamaterial

New fuel cell design powered by graphene-wrapped nanocrystals

Novel functionalized nanomaterials for carbon dioxide capture

Changing the color of single photons in a diamond quantum memory

Exploring phosphorene, a promising new material

Scientists predict promising new family of materials for solid-state cooling

What is a quantum spin liquid?

Oscillating currents point to practical application for topological insulators