Categorie: Materiale noi cu structura compozita

Nanotuburi din fibre fine – un nou material compozit realizat din nanotuburi de carbon(Fine felted nanotubes – a new composite material made of carbon nanotubes)

au dezvoltat acum o metodă alternativă, prin care tuburile mici pot fi combinate cu alte materiale, astfel încât să își păstreze proprietățile caracteristice. Ca atare, au „simțit” tuburile asemănătoare firului într-o rețea 3D stabilă, capabilă să reziste forțelor extreme.

Posted: Nov 21, 2017

Fine felted nanotubes – a new composite material made of carbon nanotubes

(Nanowerk News) Extremely lightweight, electrically highly conductive, and more stable than steel: due to their unique properties, carbon nanotubes would be ideal for numerous applications, from ultra-lightweight batteries to high-performance plastics, right through to medical implants. However, to date it has been difficult for science and industry to transfer the extraordinary characteristics at the nanoscale into a functional industrial application. The carbon nanotubes either cannot be combined adequately with other materials, or if they can be combined, they then lose their beneficial properties.
Scientists from the Functional Nanomaterials working group at Kiel University (CAU) and the University of Trento have now developed an alternative method, with which the tiny tubes can be combined with other materials, so that they retain their characteristic properties. As such, they „felt” the thread-like tubes into a stable 3D network that is able to withstand extreme forces.
The research results have now been published in Nature Communications („Hierarchical self-entangled carbon nanotube tube networks”).
thread-like carbon nanotubes
In this new process, the tiny, thread-like carbon nanotubes (CNTs) arrange themselves – almost like felting – to form a stable, tear-resistant layer. (Image: Fabian Schütt)

A difficult candidate
Industry and science have been intensively researching the significantly less than one hundred nanometre wide carbon tubes (carbon nanotubes, CNTs), in order to make use of the extraordinary properties of rolled graphene. Yet much still remains just theory. „Although carbon nanotubes are flexible like fibre strands, they are also very sensitive to changes,” explained Professor Rainer Adelung, head of the Functional Nanomaterials working group at the CAU. „With previous attempts to chemically connect them with other materials, their molecular structure also changed. This, however, made their properties deteriorate – mostly drastically.”
In contrast, the approach of the research team from Kiel and Trento is based on a simple wet chemical infiltration process. The CNTs are mixed with water and dripped into an extremely porous ceramic material made of zinc oxide, which absorbs the liquid like a sponge. The dripped thread-like CNTs attach themselves to the ceramic scaffolding, and automatically form a stable layer together, similar to a felt. The ceramic scaffolding is coated with nanotubes, so to speak. This has fascinating effects, both for the scaffolding as well as for the coating of nanotubes.
dripped CNT fibres form a thick felt-like coating around a ceramic structure
The image from the scanning electron microscope shows how the dripped CNT fibres form a thick felt-like coating around the ceramic structure. This increases its load-bearing capacity by 100,000 times. (Image: Fabian Schütt)

Following the principle of bamboo buildings
On the one hand, the stability of the ceramic scaffold increases so massively that it can bear 100,000 times its own weight. „With the CNT coating, the ceramic material can hold around 7.5kg, and without it just 50g – as if we had fitted it with a close-fitting pullover made of carbon nanotubes, which provide mechanical support,” summarised first author Fabian Schütt. „The pressure on the material is absorbed by the tensile strength of the CNT felt. Compressive forces are transformed into tensile forces.”
The principle behind this is comparable with bamboo buildings, such as those widespread in Asia. Here, bamboo stems are bound so tightly with a simple rope that the lightweight material can form extremely stable scaffolding, and even entire buildings. „We do the same at the nano-scale with the CNT threads, which wrap themselves around the ceramic material – only much, much smaller,” said Helge Krüger, co-author of the publication.

Using tiny carbon tubes to create high-performance plastics
The materials scientists were able to demonstrate another major advantage of their process. In a second step, they dissolved the ceramic scaffolding by using a chemical etching process. All that remains is a fine 3D network of tubes, each of which consists of a layer of tiny CNT tubes. In this way, the researchers were able to greatly increase the felt surface, and thus create more opportunities for reactions.
„We basically pack the surface of an entire beach volleyball field into a one centimetre cube,” explained Schütt. The huge hollow spaces inside the three-dimensional structure can then be filled with a polymer. As such, CNTs can be connected mechanically with plastics, without their molecular structure – and thus their properties – being modified. „We can specifically arrange the CNTs and manufacture an electrically conductive composite material. To do so only requires a fraction of the usual quantity of CNTs, in order to achieve the same conductivity,” said Schütt.

Simple procedure for numerous applications
Applications for use range from battery and filter technology as a filling material for conductive plastics, implants for regenerative medicine, right through to sensors and electronic components at the nano-scale. The good electrical conductivity of the tear-resistant material could in future also be interesting for flexible electronics applications, in functional clothing or in the field of medical technology, for example.
„Creating a plastic which, for example, stimulates bone or heart cells to grow is conceivable,” said Adelung. Due to its simplicity, the scientists agree that the process could also be transferred to network structures made of other nanomaterials – which will further expand the range of possible applications.
Source: Christian-Albrechts-Universität zu Kiel

Eliberarea potențialului de nano-sulf(Unleashing nano sulfur’s potential)

Nanosferele de sulf goale înfășurate în foi de disulfură de molibden ar putea forma materialul catod ideal pentru următoarea generație de baterii litiu-ion

Posted: Nov 16, 2017

Unleashing nano sulfur’s potential

(Nanowerk News) Hollow sulfur nanospheres wrapped inside sheets of molybdenum disulfide could form the ideal cathode material for the next generation of lithium-ion batteries, research from A*STAR suggests (JACS, „In situ observation and electrochemical study of encapsulated sulfur nanoparticles by MoS2 flakes”).
The amount of energy a lithium-ion battery can hold is partly determined by the amount of lithium ions its cathode can absorb. Sulfur’s high chemical affinity for lithium ions means a lithium-sulfur battery could hold five times the energy of today’s lithium-ion batteries.
Scanning electron microscopy image showing a sheet of the MoS2-wrapped sulfur nanoparticles
Scanning electron microscopy image showing a sheet of the MoS2-wrapped sulfur nanoparticles. (© ACS)
Sulfur does have drawbacks, however. Once ‘lithiated’, it becomes soluble in the battery’s electrolyte, and so can break away from the cathode. Sulfur also swells by up to 80 per cent when soaking up lithium. Both processes shorten the cathode’s life.
Complicating matters, the process by which sulfur absorbs lithium is hard to study in situ. Sulfur has a high vapor pressure, which means that its atoms rapidly sublime under the high vacuum conditions required for imaging techniques, such as transmission electron microscopy.
With an initial aim of getting a better look at sulfur during lithiation, Guangyuan Wesley Zheng from the A*STAR Institute of Materials Research and Engineering co-led an international effort to seal sulfur nanoparticles inside sheets of a 2D nanomaterial to suppress sublimation. The team selected nanoflakes of molybdenum disulfide (MoS2), a material known to have a good binding interaction with sulfur and lithium sulfide, to encase the particles.
The researchers were then able to examine the nanoparticles using transmission electron microscopy. “The most significant insight we gained related to the ‘lithiation kinetics’ of sulfur particles,” Zheng says. “We observed relatively fast lithium reaction kinetics — quite a surprise, as the common understanding is that sulfur is highly insulating, and it is difficult to directly lithiate sulfur particles.”
As well as gaining fundamental insights into lithium’s interaction with sulfur, the team showed the MoS2-wrapped hollow sulfur nanoparticles could become more than just a study tool. Sealing the sulfur within MoS2 restricted the damaging volume change and the loss of lithiated sulfur into the electrolyte, avoiding the two key hurdles blocking the use of sulfur in lithium-ion batteries.
“I do believe there is practical application for the technique in batteries, if we can further improve the MoS2 production process,” Zheng says. “We are currently exploring the scaled-up production of the encapsulated sulfur particles, and working with a battery company to develop a commercial prototype battery,” he says.
Source: A*STAR

Filtrul de apă de la Grafen se transformă în whisky clar(Graphene water filter turns whisky clear)

Membranele cu oxid de grafen, dezvoltate de Institutul Național de Graphene, au atras atenția pe scară largă asupra aplicațiilor de filtrare a apei și de desalinizare, oferind o soluție potențială pentru deficitul de apă.
Prin utilizarea membranelor ultra-subțiri, acesta este primul experiment clar pentru a arăta cum pot fi filtrați alți solvenți, demonstrând că există potențial pentru nanofiltrarea cu solvenți organici.
Graphene – primul material bidimensional din lume este cunoscut pentru superlativele sale versatilate, poate fi hidrofob și hidrofil, mai puternic decât oțel, flexibil, flexibil și de un milion de ori mai subțire decât părul uman.

Posted: Nov 13, 2017

Graphene water filter turns whisky clear

(Nanowerk News) Previously graphene-oxide membranes were shown to be completely impermeable to all solvents except for water. However, a study published in Nature Materials(„Ultrathin graphene-based membrane with precise molecular sieving and ultrafast solvent permeation”), now shows that we can tailor the molecules that pass through these membranes by simply making them ultrathin.
The research team led by Professor Rahul Nair at the National Graphene Institute and School of Chemical Engineering and Analytical Science at The University of Manchester tailored this membrane to allow all solvents to pass through but without compromising it’s ability to sieve out the smallest of particles.
In the newly developed ultrathin membranes, graphene-oxide sheets are assembled in such a way that pinholes formed during the assembly are interconnected by graphene nanochannels, which produces an atomic-scale sieve allowing the large flow of solvents through the membrane.
This new research allows for expansion in the applications of graphene based membranes from sea water desalination to organic solvent nanofiltration (OSN). Unlike sea water desalination, which separate salts from water, OSN technology separates charged or uncharged organic compounds from an organic solvent.
As an example, Manchester scientists demonstrated that graphene-oxide membranes can be designed to completely remove various organic dyes as small as a nanometre dissolved in methanol.
Prof. Nair said, “Just for a fun, we even filtered whisky and cognac through the graphene-oxide membrane. The membrane allowed the alcohol to pass through but removed the larger molecules, which gives the amber colour. The clear whisky smells similar to the original whisky but we are not allowed to drink it in the lab, however it was a funny Friday night experiment!”
The newly developed membranes not only filter out small molecules but it boosts the filtration efficiency by increasing the solvent flow rate.
Prof. Nair added “Chemical separation is all about energy, various chemical separation processes consume about half of industrial energy useage. Any new efficient separation process will minimize the consumption of energy, which is in high demand now. By 2030, the world is projected to consume 60% more energy than today.”
Dr. Su, who led the experiment added “The developed membranes are not only useful for filtering alcohol, but the precise sieve size and high flux open new opportunity to separate molecules from different organic solvents for chemical and pharmaceutical industries. This development is particularly important because most of the existing polymer-based membranes are unstable in organic solvents whereas the developed graphene-oxide membrane is highly stable.”
Graphene-oxide membranes developed at the National Graphene Institute have attracted widespread attention for water filtration and desalination applications, providing a potential solution to the water scarcity.
By using ultra-thin membranes, this is the first clear-cut experiment to show how other solvents can be filtered out, proving that there is potential for organic solvent nanofiltration.
Graphene- the world’s first two-dimensional material is known for its versatile superlatives, it can be both hydrophobic and hydrophilic, stronger than steel, flexible, bendable and one million times thinner than a human hair.
This research has changed the perception of what graphene-oxide membranes are capable of and how we can use them. By being able to design these membranes to filter specific molecules or solvents, it opens up new potential uses that have previously not been explored.
Source: University of Manchester

Materialele compozite pe bază de grafen deblochează calea către tranzistoare cu putere redusă(Graphene-based composite materials unlock the path to ultra-low-power transistors)

a descoperit un nou traseu pentru tranzistoarele cu putere redusă, folosind un material compozit pe bază de grafen. cred că soluția constă în materiale compozite realizate din monostraturi de grafen și dicalcogenide de metale tranziționale (TMDC). Au descoperit că aceste materiale ar putea fi folosite pentru a obține un control electric fin asupra procesului de rotație a electronilor, acul mic al busolei.

Posted: Nov 07, 2017

Graphene-based composite materials unlock the path to ultra-low-power transistors

(Nanowerk News) An international team of scientists has discovered a new route to ultra-low-power transistors using a graphene-based composite material.
As transistors are squeezed into ever smaller areas within computer chips, the semiconductor industry struggles to contain overheating in devices.
Now researchers from the University of York and Roma Tre University believe the solution lies in composite materials built from monolayers of graphene and the transition metal dichalcogenide (TMDC).They discovered these materials could be used to achieve a fine electrical control over the electron’s spin – its tiny compass needle.
The new research, published today in the journal Physical Review Letters („Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides”), could lead the way to much needed low-energy consumption electronics.
Lead researcher Dr Aires Ferreira, of the University of York’s Department of Physics, said: „For many years, we have been searching for good conductors allowing efficient electrical control over the electron’s spin.
„We found this can be achieved with little effort when two-dimensional graphene is paired with certain semiconducting layered materials. Our calculations show that the application of small voltages across the graphene layer induces a net polarization of conduction spins.
„We believe that our predictions will attract substantial interest from the spintronics community. The flexible, atomically thin nature of the graphene-based structure is a major advantage for applications. Also, the presence of a semiconducting component opens up the possibility for integration with optical communication networks.”
The electron’s spin is like a tiny, point-like magnet which can point only in two directions, up or down. In materials where a major fraction of electrons’ spins is aligned, a magnetic response is produced, which can be used to encode information.
‘Spin currents’ – built from ‘up’ and ‘down’ spins flowing in opposite directions – carry no net charge, and therefore in theory, produce no heating. The control of spin information would therefore open the path towards ultra-energy-efficient computer chips. The team of researchers showed that when a small current is passed through the graphene layer, the electrons’ spin polarize in plane due to ‘spin-orbital’ forces brought about by the proximity to the TMDC base. They also showed that the efficiency of charge-to-spin conversion can be quite high even at room temperature.
Manuel Offidani, a PhD student with York’s Department of Physics, carried out most of the complex calculations in this study. He said: „The current-induced polarization of the electron’s spin is an elegant relativistic phenomenon that arises at the interface between different materials.
„We chose graphene mainly because of its superb structural and electronic properties. In order to enhance the relativistic effects experienced by charge carriers in graphene, we investigated the possibility of matching it with recently discovered layered semiconductors.”
Professor Roberto Raimondi, who leads the spintronics group at Roma Tre University, said: „The possibility of orienting the electron spin with electrical currents is attracting a lot of attention in the spintronics community and arises generally as a consequence of specific symmetry conditions.
„As such this phenomenon represents a perfect example where fundamental and applied research go happily together. In this respect, our calculations demonstrate that graphene combined with the transition metal dichalcogenides is an ideal platform where abstract theoretical principles may find immediate application in showing the way to experimental and technological development.”
Current-induced spin polarization in non-magnetic media was first demonstrated in 2001 in semiconductors and, more recently, in metallic hetero-interfaces. Now the researchers predict that a similar effect occurs in graphene on TMDC monolayer.
Surprisingly they found that the unique character of electronic states in graphene enable charge-to-spin conversion efficiency of up to 94 per cent. This opens up the possibility of a graphene-based composite material becoming the basis for ultra-compact and greener spin-logic devices.
Dr Mirco Milletarì, a former member of the spintronics group at Roma Tre University, said: „This work follows insights gained from understanding fundamental laws that enabled us to envisage systems where the efficiency of charge-to-spin conversion can be optimal for technological applications. In particular, the much needed low-energy consumption electronics that will improve durability and performances of future devices.”
Source: University of York

Noua tehnică simplificată face din nanofoam metalic ușor(New, simplified technique makes light metallic nanofoam)

„Aceasta deschide o nouă platformă pentru explorări materiale interesante”, a spus el.
Noua tehnică folosește nanofire de paladiu ca blocuri de construcție. Nanofirele se pun în apă, apoi se amestecă într-o suspensie cu vibrații ultrasonice. Suspensia este rapid scufundată în azot lichid pentru a îngheța firele în loc. În cele din urmă, amestecul de gheață-nanofire este plasat într-un vid până când gheața se evaporă, lăsând în urmă o spumă pură de nanofire de paladiu. Densitatea materialului este la fel de mică ca o mie de densitate de paladiu în forma metalică în vrac și poate fi reglată pentru aplicații diferite

Posted: Nov 02, 2017

New, simplified technique makes light metallic nanofoam

(Nanowerk News) A simple method for manufacturing extremely low-density palladium nanofoams could help advance hydrogen storage technologies, reports a new study from the University of California, Davis (Chemistry of Materials, „Tunable Low Density Palladium Nanowire Foams”).
nanowire foam
UC Davis physicists Dustin Gilbert, Kai Liu and colleagues have come up with a new, simpler method to make a nanofoam of palladium. A nanofoam is a low density, porous material with very small pore size. The foamy metal could be used to store hydrogen in vehicles or for other purposes. (Image: Dustin Gilbert and Kai Liu, UC Davis)
A nanofoam is what it sounds like – a foamy version of some material, filled with very small pores. First introduced about 20 years ago, metallic nanofoams have potential for diverse applications. The porous structures are strong and lightweight – like their natural counterparts of bone and cork. Palladium and certain other metal nanofoams can also rapidly store and release hydrogen, making them an ideal candidate for hydrogen fuel cells.
But before cars can start fueling up via nanofoam, using metallic foams on an industrial scale must overcome challenges including demanding manufacturing conditions, contamination and poor crystallinity, said senior author Kai Liu, professor of physics in the UC Davis College of Letters and Science. It is also difficult to achieve extremely lightweight foams without compromising their stability, Liu noted.
Traditional metallic foam manufacturing techniques may require high temperature, high pressure and controlled chemical environments. The UC Davis-led team instead relies on a wet chemistry approach that is well-suited for industrial applications and adaptable to other types of lightweight metal foams as well, Liu said.
„This opens up a whole new platform for exciting materials explorations,” he said.
The new technique uses nanowires of palladium as building blocks. The nanowires are put in water, then mixed into a slurry with ultrasonic vibrations. The slurry is quickly immersed in liquid nitrogen to freeze the wires in place. Finally, the ice-nanowire mix is placed in a vacuum until the ice vaporizes, leaving behind a pure palladium nanowire foam. The density of the material is as low as one-thousandth of the density of palladium in it’s bulk metal form and can be tuned for different applications, the team found.
The researchers also studied the hydrogen storage properties of the palladium nanofoam, finding the material demonstrated excellent loading capacity and rate of absorption. The nanofoam exhibits excellent thermodynamic stability, as measured by specialized calorimetric techniques at the UC Davis Peter A. Rock Thermochemistry Laboratory. The laboratory is led by study co-author Alexandra Navrotsky, who holds the Edward Roessler Chair in Mathematical and Physical Science.
Source: University of California – Davis

Forța electrostatică preia polimerii bioinpuși(Electrostatic force takes charge in bioinspired polymers)

Acest avans s-ar putea dovedi util în proiectarea de noi materiale bioinpuse și inteligente pentru aplicații variind de la livrarea de medicamente până la sensibilizarea la remedierea contaminanților de mediu. O clasa de polimeri, numite coacervates, care se separa ca ulei si apa si formeaza o substanta asemanatoare cu gelul

Posted: Nov 02, 2017

Electrostatic force takes charge in bioinspired polymers

(Nanowerk News) Researchers at the University of Illinois and the University of Massachusetts, Amherst have taken the first steps toward gaining control over the self-assembly of synthetic materials in the same way that biology forms natural polymers. This advance could prove useful in designing new bioinspired, smart materials for applications ranging from drug delivery to sensing to remediation of environmental contaminants.
Proteins, which are natural polymers, use amino acid building blocks to link together long molecular chains. The specific location of these building blocks, called monomers, within these chains creates sequences that dictate a polymer’s structure and function. In the journal Nature Communications („Sequence and entropy-based control of complex coacervates”), the researchers describe how to utilize the concept of monomer sequencing to control polymer structure and function by taking advantage of a property present in both natural and synthetic polymers – electrostatic charge.
professor Charles Sing, left, and graduate students Jason Madinya and Tyler Lytle
Inspired by the principles of natural polymer synthesis, Illinois chemical and biomolecular engineering professor Charles Sing, left, and graduate students Jason Madinya and Tyler Lytle co-authored a study that found they could create new synthetic materials by tuning the electrostatic charge of polymer chains. (Photo by L. Brian Stauffer)
„Proteins encode information through a precise sequence of monomers. However, this precise control over sequence is much harder to control in synthetic polymers, so there has been a limit to the quality and amount of information that can be stored,” said Charles Sing, a professor of chemical and biomolecular engineering at Illinois and a study co-author. „Instead, we can control the charge placement along the synthetic polymer chains to drive self-assembly processes.”
„Our study focuses on a class of polymers, called coacervates, that separate like oil and water and form a gel-like substance,” said Sarah Perry, a study co-author and University of Massachusetts, Amherst chemical engineering professor, as well as an Illinois alumna.
Through a series of experiments and computer simulations, the researchers found that the properties of the resulting charged gels can be tuned by changing the sequence of charges along the polymer chain.
„Manufacturers commonly use coacervates in cosmetics and food products to encapsulate flavors and additives, and as a way of controlling the ‘feel’ of the product,” Sing said. „The challenge has been if they need to change the texture or the thickness, they would have to change the material being used.”
Sing and Perry demonstrate that they can rearrange the structure of the polymer chains by tuning their charge to engineer the desired properties. „This is how biology makes the endless diversity of life with only a small number of molecular building blocks,” Perry said. „We envision bringing this bioinspiration concept full circle by using coacervates in biomedical and environmental applications.”
The results of this research open a tremendous number of opportunities to expand the diversity of polymers used and the scale of applications, the researchers said. „Currently, we are working with materials on the macro scale – things that we can see and touch,” Sing said. „We hope to expand this concept into the realm of nanotechnology, as well.”
Source: University of Illinois at Urbana-Champaign

Studiile noi privind catodii dezordonați pot furniza baterii de litiu foarte necesare(New studies on disordered cathodes may provide much-needed jolt to lithium batteries)

„Materialele catodice noi reprezintă direcția cea mai fierbinte în bateriile Li-ion”, a spus Ceder. „Câmpul este un pic blocat.Pentru a obține mai multe îmbunătățiri în stocarea de energie există doar câteva direcții de a merge.Una este baterii solid-state, iar cealaltă este de a continua să îmbunătățească densitatea de energie a materialelor electrod.Două nu sunt reciproc exclusiv această linie de cercetare nu este încă epuizată. „

Posted: Oct 30, 2017

New studies on disordered cathodes may provide much-needed jolt to lithium batteries

(Nanowerk News) Today’s lithium-ion battery was invented so long ago, there are not many more efficiencies to wring out of it. Now researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) report major progress in cathodes made with so-called „disordered” materials, a promising new type of lithium battery.
In a pair of papers published this month in Nature Communications („Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials”) and Physical Review Letters („Electronic-Structure Origin of Cation Disorder in Transition-Metal Oxides”), a team of scientists led by Gerbrand Ceder has come up with a set of rules for making new disordered materials, a process that had previously been driven by trial-and-error. They also found a way to incorporate fluorine, which makes the material both more stable and have higher capacity.
„This really seems to be an interesting new direction for making high energy density cathodes,” said Ceder, a Senior Faculty Scientist at Berkeley Lab who also has an appointment at UC Berkeley’s Department of Materials Science and Engineering. „It’s remarkable that all the disordered rock salts people have come up with so far have very high battery capacity. In the PRL paper we give a guideline for how to more systematically make these materials.”
Gerbrand Ceder
A team of scientists led by Gerbrand Ceder reported major progress in cathodes made with so-called „disordered” materials, a promising new type of lithium battery. (Image: Berkeley Lab)

The benefits of disorder
The cathode material in lithium batteries is typically „ordered,” meaning the lithium and transition metal atoms are arranged in neat layers, allowing lithium to move in and out of the layers. A few years ago, Ceder’s group discovered that certain types of disordered material could store even more lithium, giving batteries higher capacity.
The lead author of the PRL paper is Alexander Urban, a Berkeley Lab postdoctoral fellow.
„Despite their attractive properties, discovering new disordered materials has been mostly driven by trial-and-error and by relying on human intuition,” Urban said. „Now we have for the first time identified a simple design criterion to predict novel disordered compositions. The new understanding establishes a relationship between the chemical species, local distortions of the crystal structure, and the tendency to form disordered phases.”
The other advantage of using disordered materials is the ability to avoid the use of cobalt, a limited resource, with more than half the world’s supply existing in politically unstable countries. By moving to disordered rock salts, battery designers could be free to use a wider range of chemistries. For example, disordered materials have been made using chromium, titanium, and molybdenum.
„We want the ability to have more compositional freedom, so we can tune other parameters,” Ceder said. „There are so many properties to optimize – the voltage, the long-term stability, whether it’s easy to synthesize – there’s so much that goes into taking a battery material to a commercial stage. Now we have a recipe for how to make these materials.”

How and why to fluorinate batteries
Another major advance in lithium-ion batteries is reported in the Nature Communications paper, which shows that disordered materials can be fluorinated, unlike other battery materials. Fluorination confers two advantages: it allows more capacity and makes the material more stable. In a battery, the increased stability would translate into a device with long cycle life and that is less likely to catch fire.
The lead author of the paper, Jinhyuk Lee, formerly a Berkeley Lab researcher, worked with scientists at Berkeley Lab’s Advanced Light Source (ALS), a source of X-ray beams for scientific research, to conduct in situ experiments. „The ALS was really important to understand the mechanism by which we get higher capacity,” Ceder said. „What’s really cool is you can look at the battery while it’s operating, and look at the electronic structure of the cathodes. So you learn how it charges and discharges, where the electrons go, which is a crucial aspect of charge storage.”
ALS scientists Shawn Sallis and Wanli Yang are co-authors, as is Bryan McCloskey of Berkeley Lab. „His group was crucial in showing these materials are more stable and don’t lose oxygen,” Ceder said.
Now that they have demonstrated the concept, Ceder plans to follow up by trying to add even more fluorine to the materials.
„New cathode materials is the hottest direction in Li-ion batteries,” Ceder said. „The field is a bit stuck. To get more improvements in energy storage there are only a few directions to go. One is solid-state batteries, and the other is to keep improving the energy density of electrode materials. The two are not mutually exclusive. This research line is definitely not exhausted yet.”
Source: Lawrence Berkeley National Laboratory

Ghidarea laserului aleatoriu(Guiding the random laser)

Cercetătorii sunt capabili să obțină aceste rezultate prin fabricarea și utilizarea unei fibre optice din fibră optică Anderson. Fibra este fabricată dintr-un „cuart satinos”, un geam artizan extrem de poros, utilizat în mod obișnuit doar pentru calibrarea mașinilor care atrag fibră optică. Când este tras în bucle lungi, materialul poros formează zeci de canale microscopice de aer în fiecare fibră.Echipa de cercetare a fabricat un nou tip de fibră optică care este capabilă să controleze aceste lasere aleatorii.

Posted: Oct 27, 2017

Guiding the random laser

(Nanowerk News) At its most basic level, a random laser is precisely what its name implies; random. It’s random in the spectrum of light it produces and in the way that light is emitted, making what could be an extremely versatile laser source, nearly useless for most practical applications.
So, how do you control some of the randomness to make useful devices? It’s a question that’s led a team of researchers at The University of New Mexico to a discovery that’s taking laser technology to the next level.
„It’s been incredible to see how this project has progressed,” said Behnam Abaie, a Ph.D. student at UNM’s Center for High Technology Materials (CHTM). „When I first came to work with Professor [Arash] Mafi, I knew this project had the potential to be very successful but I never expected this.”
Abaie is the first-author on a paper recently published in Nature’s Light: Science & Applications („Random lasing in an Anderson localizing optical fiber”). The article provides a technical analysis of how the research team, led by CHTM Interim Director Arash Mafi, is able to reliably control these extremely powerful, but previously uncontrollable, lasers.
Glass Anderson Localized Optical Fiber
The research team fabricated a new type of optical fiber that is capable of controlling these random lasers. (Image: University of New Mexico)
„Our success in being able to control these random lasers addresses decade-old issues that have prevented these lasers from becoming mainstream devices,” said Mafi, who is also an associate professor in UNM’s Dept. of Physics & Astronomy. „It’s a very exciting contribution.”
Traditional lasers consist of three main components: an energy source, gain medium and optical cavity. The energy source is provided through a process called ‘pumping’ and can be supplied through an electrical current or another light source. That energy then passes through the gain medium which contains properties that amplify the light. The optical cavity ­- a pair of mirrors on either side of the gain medium – bounce the light back and forth through the medium, amplifying it each time. The result is a directed, intense beam of light called a laser.
Random lasers, by comparison, perform using a pump, a highly-disordered gain medium but no optical cavity. They are extremely useful due to their simplicity and broad spectral features, meaning a single random laser can produce a beam of light containing multiple spectra, a very beneficial property for certain applications like biomedical imaging. However, given their nature, random lasers are difficult to reliably control due to their multi-directional output and chaotic fluctuation.
The UNM team, in collaboration with researchers at Clemson University and the University of California San Diego, has been able to overcome these obstacles in an efficient way – a victory they hope will continue to push the use of random lasers forward.
„Our device has all the great qualities of a random laser, plus spectral stability and it is highly directional,” said Mafi. „It’s a wonderful development.”
Researchers are able to achieve these results through the fabrication and use of a unique glass Anderson localizing optical fiber. The fiber is made of a ‘satin quartz’, an extremely porous artisan glass that is typically only used to calibrate the machinery that draws fiber optics. When pulled into long rods, the porous material forms dozens of microscopic air channels in each fiber.
„The glass that we’re using for these fiber optics is actually material that we would typically throw away because it is very porous,” said Abaie. „But, it’s those holes in the glass that are actually creating the channels that control the laser.”
Once filled with a gain medium and pumped using a single-colored green laser, the random laser becomes less random and highly controllable, thanks to a phenomenon known as Anderson Localization.
„There is still a lot to learn about Anderson Localization but it’s exciting for us to be part of this development,” said Mafi. „To be able to actually make devices that utilize this phenomenon, it’s taking the science to yet another level.”
Mafi and his research team are some of the leading experts in Anderson Localization. In 2014, they published an article on a different device capable of transmitting images using the phenomenon. That research was named one of Physics World’s Top Ten Breakthroughs of the year.
Moving forward, Mafi says they hope to broaden the spectrum of this new device and make it more efficient, creating a broad spectrum illumination source that can be utilized around the world.
Source: University of New Mexico

Dispozitivele fabricate din materiale 2D separă sărurile din apa de mare(Devices made from 2D materials separate salts in seawater)

Frezele sunt realizate din grafen, nitrură de bor hexagonală (hBN) și disulfură de molibden (MoS 2 ) și, în mod surprinzător, permit ionilor cu diametre mai mari decât dimensiunea fantei să treacă prin. Studiile de excludere a dimensiunilor permit o mai bună înțelegere a modului în care funcționează filtre biologice similare la scară largă, cum ar fi aquaporins, și astfel vor contribui la dezvoltarea unor filtre cu flux înalt pentru desalinizarea apei și a tehnologiilor aferente.

Posted: Oct 26, 2017

Devices made from 2D materials separate salts in seawater

(Nanowerk News) Researchers at the National Graphene Institute (NGI) at The University of Manchester have succeeded in fabricating tiny slits in a new membrane that are just several angstroms (0.1nm) in size. This has allowed the study of how various ions pass through these tiny holes.
The slits are made from graphene, hexagonal boron nitride (hBN) and molybdenum disulphide (MoS2) and, surprisingly, allow ions with diameters larger than the size of the slit to permeate through. The size-exclusion studies allow for a better understanding of how similar scale biological filters such as aquaporins work and so will help in the development of high-flux filters for water desalination and related technologies.
2D materials have been successfully assembled into devices with the smallest possible man made holes for water desalination
2D materials have been successfully assembled into devices with the smallest possible man made holes for water desalination. (University of Manchester)
For scientists interested in the behaviour of fluids and their filtration, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and individual water molecules.
Researchers have been trying to mimic naturally-occurring ion transport systems, but this has proved to be no easy task. Channels fabricated with standard techniques and conventional materials have unfortunately been limited in size by the intrinsic roughness of a material’s surface, which is usually at least ten times bigger than the hydrated diameter of small ions.
Earlier this year graphene-oxide based membranes developed at the NGI attracted considerable attention as promising candidates for new filtration technologies. This research utilising the new toolkit of 2D materials demonstrates the real-world potential of providing clean drinking water from salt water.
To better understand the fundamental mechanisms behind ion transport, a team led by Sir Andre Geim of The University of Manchester made atomically flat slits measuring just several angstroms in size. These channels are chemically inert with smooth walls on the angstrom scale.
The researchers made their slit devices from two 100-nm thick crystal slabs of graphite measuring several microns across that they obtained by shaving off bulk graphite crystals. They then placed rectangular-shaped pieces of 2D atomic crystals of bilayer graphene and monolayer MoS2 at each edge of one of the graphite crystal slabs before placing another slab on top of the first. This produces a gap between the slabs that has a height equal to the spacers’ thickness.
“It’s like taking a book, placing two matchsticks on each of its edges and then putting another book on top.” explains Geim. “This creates a gap between the books’ surfaces with the height of the gap being equal to the matches’ thickness. In our case, the books are the atomically flat graphite crystals and the matchsticks the graphene or MoS2 monolayers.”
The assembly is held together by van der Waals forces and the slits are roughly the same size as the diameter of aquaporins, which are vital for living organisms. The slits are the smallest size possible since slits with thinner spacers are unstable and collapse because of attraction between opposite walls.
Ions flow through the slits if a voltage is applied across them when they are immersed in an ionic solution, and this ion flow constitutes an electric current. The team measured the ionic conductivity as they passed through chloride solutions via the slits and found that ions could move through them as expected under an applied electric field.
“When we looked more carefully, we found that bigger ions moved through more slowly than smaller ones like potassium chloride” explains Dr Gopi Kalon, a postdoctoral researcher who led the experimental effort.
Dr Ali Esfandiar, who is the first author of the paper, adds “The classical viewpoint is that ions with a diameter larger than the slit size cannot permeate, but our results show that this explanation is too simplistic. Ions in fact behave like soft tennis balls rather than hard billiard ones, and large ions can still pass – either by distorting their water shells or maybe shedding them altogether.
The new research as published in Science, shows that these newly observed mechanisms plays a key role for desalination using the size exclusion and is a key step to creating high-flux water desalination membranes.
Source: University of Manchester

Cercetătorii introduc un nou catalizator pentru bateriile reîncărcabile metal-aer(Researchers introduce novel catalyst for rechargeable metal-air batteries)

Noul lor catalizator posedă structura de materiale perovskite pe bază de nanofibre și prezintă performanțe electrochimice excelente, apropiate de cele ale catalizatorilor de metale prețioase de astăzi, dar totuși

Posted: Oct 25, 2017

Researchers introduce novel catalyst for rechargeable metal-air batteries

(Nanowerk News) Research in lithium-ion batteries has opened up a plethora of possibilities in the development of next-generation batteries. In particular, the metal-air batteries with significantly greater energy density close to that of gasoline per kilogram, has recently been acknowledged and invested by world’s leading companies, like IBM.
A recent study („A Highly Efficient and Robust Cation Ordered Perovskite Oxide as a Bifunctional Catalyst for Rechargeable Zinc-Air Batteries”) has presented novel catalyst to accelerate the commercialization of metal-air batteries.
This breakthrough has been jointly led by Professor Guntae Kim and Professor Jaephil Cho in the School of Energy and Chemical Engineering at UNIST in collaboration with Professor Yunfei Bu from Nanjing University of Science and Technology, Nanjing, China. Their new catalyst possesses the structure of nanofiber-based perovskite materials and exhibits excellent electrochemical performance, close that of today’s precious metal catalysts, yet still inexpensive.
Mesoporous nanofiber of cation ordered perovskite was prepared via electrospinning process
Mesoporous nanofiber of cation ordered perovskite was prepared via electrospinning process, which exhibited notable cell performance and exceptionally high stability for Zn-air battery. (Image: UNIST)
A metal-air battery is a type of fuel cell or battery that uses the oxidation of a metal with oxygen from atmospheric air to produce electricity. It is equipped with an anode made up of pure metals – like lithium or zinc – and an air cathode that is connected to an inexhaustible source of air. The catalysts in the air cathode aids the electrochemical reaction of the cell with oxygen gas. Metal-air batteries have attracted significant research attention as the new generation of high-performance batteries as they the advantages of (1) simple structure, (2) extremely high energy density, and (3) a relatively inexpensive production.
The currently existing metal-air batteries use rare and expensive metal catalysts for their air electrodes, such as platinum (Pt) and iridium oxide (IrO2). This has hindered its further commercialization into the marketplace.
In the study, Professor Kim and his research team have developed a new catalyst, using the cation ordered double perovskite with high electrical conductivity and catalyic performance. They prepared a series of PrBa0.5Sr0.5Co2-xFexO5+δ (x = 0, 0.5, 1, 1.5, and 2, PBSCF) and determined the optimum cobalt (Co) and iron (Fe) contents through electrochemical evaluation.
OER activities of PBSCF-NF, PBSCF-P, BSCF and IrO2.
OER activities of PBSCF-NF, PBSCF-P, BSCF and IrO2. (Image: UNIST)
„The structure of mesoporous PrBa0.5Sr0.5Co2-xFexO5+δ nanofiber (PBSCF-NF) has high surface areas, result from uniform pore diameters,” says Ohhun Gwon in the Combined M.S/Ph.D. of Energy and Chemical Engineering, the first author of the study. „This nanofiber has also brought significant improvements in the performance of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).”
According to the research team, this nanofiber has improved the bi-functionality of ORR/OER. Particularly, the OER performance was about 9 times higher than that of state-of-the-art precious metal oxide IrO2 at overpotential of 0.3 V. Furthermore, it also demonstrated notable charge-discharge stability even at high current density in Zn-air batteries.
„We envision that the high electrochemical and catalytic performance of this material will play a major role in the commercialization of metal-air batteries,” says Professor Kim. „Metal-air battery technology is still in its infancy and extensive additional research efforts appear to be required before a viable commercial implementation is developed.”
He adds, „However, as many global corporates, such as IBM, Toyota, and Samsung Electronics are already working on the development of metal-air batteries, the technical challenges could soon be cleared out in a much faster pace than anticipated.”
Source: Ulsan National Institute of Science and Technology

Un lichid cu spin quantum(A quantum spin liquid)

au creat un material structurat în formă de fagure evaziv capabil să frustreze proprietățile magnetice din interiorul acestuia pentru a produce o entitate chimică cunoscută sub numele de „lichid de centrifugare”, teoretizată ca o poartă către fluxul liber proprietăți ale computerelor cuantice.Iridatul de cupru este un izolator – electronii sunt imobilizați în solid – dar pot transporta în continuare un moment magnetic cunoscut sub numele de „spin”. Transportul de rotiri gratuite în material permite un flux de informații cuantice.

Posted: Oct 24, 2017

A quantum spin liquid

(Nanowerk News) Researchers from Boston College and Harvard have created an elusive honeycomb-structured material capable of frustrating the magnetic properties within it in order to produce a chemical entity known as „spin liquid,” long theorized as a gateway to the free-flowing properties of quantum computing, according to a new report in the Journal of the American Chemical Society („Cu2IrO3: A New Magnetically Frustrated Honeycomb Iridate”).
The first-of-its-kind copper iridate metal oxide – Cu2IrO3 – is one where the natural magnetic order is disrupted, a state known as geometric frustration, said Boston College Assistant Professor of Physics Fazel Tafti, a lead author of the study, titled Cu2IrO3: a new magnetically frustrated honeycomb iridate.
Copper Iridate Metal Oxide
Scientists from Boson College and Harvard turned to copper to create a first-of-its-kind iridate – Cu2IrO3 – where the natural magnetic order is disrupted, a state known as geometric frustration. (Image: Boston College) (click on image to enlarge)
The copper iridate is an insulator – its electrons are immobilized in the solid – but they can still transport a magnetic moment known as „spin”. The transport of free spins in the material allows for a flow of quantum information.
The Kitaev model, proposed in 2006 by Cal Tech Professor of Physics Alexei Kitaev, states that a hexagonal honeycomb structure offered a promising route to geometric frustration and therefore, to quantum spin liquid.
Only two honeycomb lattice have been successfully developed in an attempt to fulfill Kitaev’s model: a lithium iridate (Li2IrO3) and a sodium iridate (Na2IrO3). Yet both fell short of achieving an ideal spin liquid due to magnetic ordering, said Tafti, who co-authored the paper with Boston College post-doctoral researchers Mykola Abramchuk and Jason W. Krizan, BC Adjunct Professor of Chemistry and Director of Advanced Chemistry Laboratories Kenneth R. Metz, and Harvard’s David C. Bell and Cigdem Ozsoy-Keskinbora.
Tafti and his team turned to copper due to its ideal atomic size, which is between lithium and sodium. Their studies in x-ray crystallography found subtle flaws in the honeycombs formed in the lithium and sodium iridates. The team swapped copper for sodium in what Tafti termed a relatively simple „exchange” reaction. The effort produced the first oxide of copper and iridium, Tafti said.
„Copper is ideally suited to the honeycomb structure,” said Tafti. „There is almost no distortion in the honeycomb structure.”
A decade after the original prediction of quantum spin liquid on a honeycomb lattice by Kitaev, the young team of scientists from Boston College succeeded in making a material that almost exactly corresponds to the Kitaev model, Tafti said.
Tafti’s lab will pursue the „exchange” chemistry path to make new forms of honeycomb materials with more exotic magnetic properties, he said.