Lună: noiembrie 2017

Observarea atomilor care se deplasează în cristale perovskite hibride dezvăluie indicii pentru îmbunătățirea celulelor solare(Watching atoms move in hybrid perovskite crystals reveals clues to improving solar cells)

Utilizând raze X și lasere, cercetătorii au studiat modul în care o nouă clasă promițătoare de materiale cu celule solare, numite perovskite hibride, se comportă la nivel de nanometrie în timpul funcționării. Experimentele lor au arătat că atunci când se aplică tensiune, ionii migrează în interiorul materialului, creând zone care nu mai sunt la fel de eficiente la conversia luminii în energie electrică.cercetătorii au strălucit un laser pe cristale pentru a măsura o proprietate numită fotoluminescență – capacitatea materialului de a emite lumină când este excitată de un laser – în diferite zone ale cristalelor. Un bun material cu celule solare emit foarte bine lumina, deci cu cât este mai mare fotoluminescența, cu atât este mai eficientă celula solară. Zonele cu concentrații mai mari de brom au avut o fotoluminescență mai mare cu 180% decât zonele epuizate de ioni de brom.

Posted: Nov 21, 2017

Watching atoms move in hybrid perovskite crystals reveals clues to improving solar cells

(Nanowerk News) A team of researchers led by the University of California San Diego has for the first time observed nanoscale changes deep inside hybrid perovskite crystals that could offer new insights into developing low-cost, high-efficiency solar cells.
Using X-ray beams and lasers, researchers studied how a new promising class of solar cell materials, called hybrid perovskites, behaves at the nanoscale level during operation. Their experiments revealed that when voltage is applied, ions migrate within the material, creating regions that are no longer as efficient at converting light to electricity.
„Ion migration hurts the performance of the light absorbing material. Limiting it could be a key to improving the quality of these solar cells,” said David Fenning, a professor of nanoengineering and member of the Sustainable Power and Energy Center at UC San Diego.
Perovskite Photoluminescence
The inside back cover image of the Nov. 20, 2017 issue of Advanced Materials illustrates how ion migration in a hybrid perovskite crystal affects solar cell performance in different areas of the crystal. (Image: AMOLF)
The team, led by Fenning, includes researchers from the AMOLF Institute in the Netherlands and Argonne National Laboratory. Researchers published their findings in Advanced Materials („Direct Observation of Halide Migration and its Effect on the Photoluminescence of Methylammonium Lead Bromide Perovskite Single Crystals”).
Hybrid perovskites are crystalline materials made of a mixture of both inorganic and organic ions. They are promising materials for making next-generation solar cells because they are inexpensive to manufacture and are considerably efficient at converting light to electricity.
However, hybrid perovskites are not very stable, which can make them difficult to study. Microscopic techniques typically used to study solar cells often end up damaging the hybrid perovskites or can’t image beyond their surfaces.
Now, a UC San Diego-led team has shown that by using a technique called nanoprobe X-ray fluorescence, they can probe deep into hybrid perovskite materials without destroying them. „This is a new window to peer inside these materials and see precisely what’s going wrong,” Fenning said.
The researchers studied a type of hybrid perovskite called methylammonium lead bromide, which contains negatively charged bromine ions. Like other hybrid perovskites, its crystalline structure contains many vacancies, or missing atoms, which have been suspected to allow ions to move readily within the material when a voltage is applied.
The researchers first performed nanoprobe X-ray fluorescence measurements on the crystals to create high-resolution maps of the atoms inside the material. The maps revealed that when voltage is applied, the bromine ions migrate from negatively charged areas to positively charged areas.
Next, the researchers shined a laser on the crystals to measure a property called photoluminescence – the material’s ability to emit light when excited by a laser – in different areas of the crystals. A good solar cell material emits light very well, so the higher the photoluminescence, the more efficient the solar cell should be. The areas with higher bromine concentrations had up to 180 percent higher photoluminescence than areas depleted of bromine ions.
„We watch the bromine ions migrate within minutes and see that the resulting bromine-rich areas have the potential to become better solar cells while the performance is degraded in bromine-poor areas,” Fenning said. Fenning and his team are now exploring ways to limit bromine migration in methylammonium lead bromide and other hybrid perovskites. Researchers say that one potential option would be growing hybrid perovskite crystals in different conditions to minimize the number of vacancies and limit ion migration in the crystalline structure.
Source: University of California – San Diego

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

Dezvoltarea „ABC” pentru exploatarea noilor fenomene în interacțiunile ușoare(Developing ‘ABCs’ for exploiting new phenomena in light-matter interactions)

O clasă unică de materiale manipulate de lumină, cunoscute sub denumirea de metamateriale sau materiale structurate, utilizează modele de lungimi de undă puternic interacționate sau elemente cu dimensiuni de lungime de undă. Datorită acestor structuri interne și superficiale complexe, au apărut noi proprietăți, unele dintre ele prezentând un comportament care a dus la rescrierea „legilor” de lungă durată în ceea ce privește modul în care lumina și alte unde electromagnetice (EM) interacționează cu materialele;Aplicațiile specifice includ vizibilitatea nocturnă, reflectarea căldurii și gestionarea în motoarele aeronavelor și reglarea temperaturii electronice pe sateliți în zonele extreme de temperatură și temperatură.

Posted: Nov 20, 2017

Developing ‘ABCs’ for exploiting new phenomena in light-matter interactions

(Nanowerk News) A unique class of engineered light-manipulating materials, known as metamaterials or structured materials, makes use of patterns of strongly interacting wavelength or sub-wavelength-sized elements. Because of these intricate internal and surface structures, new properties have emerged, some exhibiting behavior that has resulted in rewriting long-understood “laws” for how light and other electromagnetic (EM) waves interact with materials. These materials have been opening up new options for controlling EM waves in many technological arenas, among them imaging, thermal control, and frequency conversion. Specific applications include night-vision, heat reflection and management in aircraft engines, and temperature regulation of electronics on satellites in the hot-and-cold extremes of space.
how an engineered material might be able to convert, generate, or harvest electromagnetic fields exploiting interactions
DARPA’s Nascent Light-Matter Interactions (NLM) program aims to develop theory-anchored models that could yield new structures for materials with never-before-seen electromagnetic properties. This artist’s concept depicts an example of how an engineered material might be able to convert, generate, or harvest electromagnetic fields exploiting interactions that could have far-reaching effects in areas such as sensing, thermal control, frequency conversion, and dynamics.
Although researchers have been taking steps toward putting these materials to practical use, they remain puzzled about the optimal structure designs for desired matter-light interactions. They have yet to model the materials in ways that enable predictions about how specific structured materials will behave under different conditions, such as increased illumination intensities. To fill in these knowledge gaps, DARPA today announced the Nascent Light-Matter Interactions (NLM) program, which seeks to finally develop theory-anchored models that can expand the state of the art in already-observed phenomena while pointing to never-before-realized and new functionality.
“Recent advances in our understanding of light-matter interactions have revealed nascent concepts that could yield new materials with properties way beyond anything we have now,” said Mike Fiddy, DARPA program manager. “Through NLM we aim to identify building blocks to better understand the physics of 2-D and 3-D structured materials, which can then lead to a systematic design approach for controlling electromagnetic waves through these materials. The end goal is to equip designers with rigorous predictive models and design tools to answer the currently elusive question: ‘If I want a material with X property, how do I build it?’”
For example, can we open new pathways for designing materials that provide more efficiency in up-conversion or down conversion of frequencies, which could benefit military capabilities such as night vision? “At the moment, the state-of-the-art of these complicated structures is you pump them with one frequency and they’ll emit maybe 10 percent at another frequency, but they require lots of power in the process,” he said. “Can we develop design tools to create materials with 80, 90, or 100 percent efficiency in converting infrared light into visible light that require very little or no power?”
As Fiddy sees it, lessons learned in the NLM program also might help engineers design better materials, for example, that automatically block the frequency of a laser if it’s shined directly into the eye. Another example is managing extremely hot temperatures, such as those found in turbine aircraft engines. New engineered materials could help precisely manage temperatures in critical hot parts of the engine, which in turn could lead to more efficiency, thus reducing fuel and maintenance costs.
“Similarly, on satellites, as they orient toward the sun they can get ‘cooked’ and when they are out of the sun they are very cold,” Fiddy said. “Those big temperature extremes have to be controlled somehow in the satellite’s design. But if there were more efficient ways of radiating away the sun’s heat using structured materials, that would be very valuable. A general approach to solving this problem could be beneficial for keeping computer chips cool while at the same time opening up new ways to harvest electromagnetic energy.”
It could take years to realize such possibilities, Fiddy noted, but he hopes the NLM program will deliver new levels of understanding and modeling tools that could hasten that day. As such, he added, this new program should benefit existing programs, such as EXTREME, which focuses on specific uses for engineered materials.
The NLM program will unfold in three phases. The first will challenge performers to develop a model and show that it can predict new phenomena and serve as a design tool. The second phase will push researchers to test the models’ actual utility for identifying new materials useful for specific applications. The goal for Phase 3 is to identify specific challenge problems and tie selected performers and their respective focus and applications to the operational needs of DoD stakeholders.
DARPA announced a webcast Proposers Day for potential NLM proposers on Nov. 28, 2017. A Special Notice with registration information and other details is available here: https://go.usa.gov/xnWut. A Broad Agency Announcement (BAA) solicitation will be posted on FBO in the near future.
Source: DARPA

Borofenul strălucește singur ca material plasmonic 2-D(Borophene shines alone as 2-D plasmonic material)

Un film cu grosime de atom de bor ar putea fi primul material bidimensional pur, capabil să emită lumină vizibilă și aproape infraroșie prin activarea plasmonilor;Tehnicile actuale de nanostructurare au reușit să reducă în mod semnificativ conductivitatea termică a acestor materiale, îmbunătățind astfel performanțele lor. Un factor de putere ridicat este, de asemenea, necesar pentru generarea eficientă a energiei, însă îmbunătățirea acestuia a fost limitată deoarece necesită creșterea simultană a puterii termice a materialului și a conductivității sale electrice, ceea ce este dificil. Conductivitatea electrică a rămas scăzută datorită impurităților ionizate din material care suprimă mobilitatea electronilor.

Posted: Nov 20, 2017

Borophene shines alone as 2-D plasmonic material

(Nanowerk News) An atom-thick film of boron could be the first pure two-dimensional material able to emit visible and near-infrared light by activating its plasmons, according to Rice University scientists.
That would make the material known as borophene a candidate for plasmonic and photonic devices like biomolecule sensors, waveguides, nanoscale light harvesters and nanoantennas.
borophene
Rice University scientists calculate that the atom-thick film of boron known as borophene could be the first pure two-dimensional material naturally able to emit visible and near-infrared light by activating its plasmons. The Rice team tested models of three polymorphs and found that triangular borophene, at left, was capable of emitting visible light, while the other two reached near-infrared. (Illustration: Sharmila Shirodkar)
Plasmons are collective excitations of electrons that flow across the surface of metals when triggered by an input of energy, like laser light. Significantly, delivering light to a plasmonic material in one color (determined by the light’s frequency) can prompt the emission of light in another color.
Models by Rice theoretical physicist Boris Yakobson and his colleagues predict that borophene would be the first known 2-D material to do so naturally, without modification.
The lab’s simulations are detailed in a paper by Yakobson with lead authors Yuefei Huang, a graduate student, and Sharmila Shirodkar, a postdoctoral researcher, in the Journal of the American Chemical Society („Two-Dimensional Boron Polymorphs for Visible Range Plasmonics: A First-Principles Exploration”).
Boron is a semiconductor in three dimensions but a metal in 2-D form. That prompted the lab to have a look at its potential for plasmonic manipulation.
“This was kind of anticipated, but we had to do careful work to prove and quantify it,” said Yakobson, whose lab often predicts possible materials that experimentalists later make, like borophene or the boron buckyball. With colleagues Evgeni Penev, an assistant research professor at Rice, and alumnus Zhuhua Zhang, he recently published an extensive review of the state of boron research.
In the new study, the researchers used a computational modeling technique called density functional theory to test plasmonic behavior in three types of free-standing borophene. The material’s baseline crystal structure is a grid of triangles — think graphene but with an extra atom in the middle of each hexagon.
The lab studied models of plain borophene and two polymorphs, solids that incorporate more than one crystalline structure that are formed when some of those middle atoms are removed. Their calculations showed triangular borophene had the widest emission frequencies, including visible light, while the other two reached near-infrared.
“We don’t have enough experimental data to determine which mechanisms contribute how much to the losses in these polymorphs, but we anticipate and include scattering of plasmons against defects and excitation of electrons and holes that lead to their damping,” Shirodkar said.
The researchers said their results present the interesting possibility of manipulating data at subdiffraction wavelengths.
“If you have an optical signal with a wavelength that’s larger than an electronic circuit of a few nanometers, there’s a mismatch,” she said. “Now we can use the signal to excite plasmons in the material that pack the same information (carried by the light) into a much smaller space. It gives us a way to squeeze the signal so that it can go into the electronic circuit.”
“It turns out that’s important because, roughly speaking, it can improve the resolution by 100 times, in some cases,” Yakobson said. “Resolution is limited by wavelength. By using plasmons, you can store information or write into a material at a much higher resolution because of the shrinkage of the wavelength. This could have great benefits for data storage.”
Experimentalists have made borophene only in very small amounts so far and lack methods to transfer the material from the surfaces on which its grown, Yakobson said. Still, there’s plenty for theoretical scientists to study and plenty of progress in the labs.
“One should explore other polymorphs and look for the best one,” Yakobson suggested. “Here, we didn’t. We just considered three, because it’s pretty heavy work — but others need to be screened before we know what is achievable.”
Source: By Mike Williams, Rice University

Curează curentul de căldură: materialul nou mărește eficiența(Spin current from heat: New material increases efficiency)

Studiul lor nou determină rezistența curentului de rotație pentru diverse combinații de filme subțiri.
Un curent de rotație este produs de diferențele de temperatură dintre cele două capete ale unei componente electronice. Aceste componente sunt extrem de mici și doar o milionime de grosime de milimetru. Deoarece sunt compuse din materiale magnetice, cum ar fi fier, cobalt sau nichel, ele sunt numite nanostructuri magnetice. Potrivit cercetătorilor, nanostructurile magnetice cu combinații speciale alcătuite din cobalt, fier, siliciu și aluminiu au fost deosebit de productive.

Posted: Nov 20, 2017

Spin current from heat: New material increases efficiency

(Nanowerk News) Electronic devices such as computers generate heat that mostly goes to waste. Physicists at Bielefeld University have found a way to use this energy: They apply the heat to generate magnetic signals known as ‘spin currents’. In future, these signals could replace some of the electrical current in electronic components.
In a new study, the physicists tested which materials can generate this spin current most effectively from heat. The research was carried out in cooperation with colleagues from the University of Greifswald, Gießen University, and the Leibniz Institute for Solid State and Materials Research in Dresden.
Their findings are being published in Nature Communications („Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes”).
researcher in the lab
In experiments, including those at the University of Greifswald, researchers are testing which material can generate spin current most effectively. (Image: University of Greifswald)
The Bielefeld physicists are working on the basic principles for making data processing more effective and energy-efficient in the young field of ‘spin caloritronics’. They are members of the ‘Thin Films & Physics of Nanostructures’ research group headed by Professor Dr. Günter Reiss. Their new study determines the strength of the spin current for various combinations of thin films.
A spin current is produced by differences in temperature between two ends of an electronic component. These components are extremely small and only one millionth of a millimetre thick. Because they are composed of magnetic materials such as iron, cobalt, or nickel, they are called magnetic nanostructures.
The physicists take two such nanofilms and place a layer of metal oxide between them that is only a few atoms thick. They heat up one of the external films – for example, with a hot nanowire or a focused laser. Electrons with a specific spin orientation then pass through the metal oxide. This produces the spin current. A spin can be conceived as electrons spinning on their own axes – either clockwise or anti-clockwise.
In their new study, Dr. Alexander Böhnke and Dr. Torsten Hübner together with their colleagues Dr. Timo Kuschel and Privatdozent Dr. Andy Thomas tested different combinations of ultra-thin films. Each time, they heated one of the external films in the same way. ‘Depending on which material we used, the strength of the spin current varied markedly,’ says Böhnke. ‘That is because of the electronic structure of the materials we used.’
Based on theoretical assumptions, the researchers were able to find suitable materials possessing the appropriate electronic structure. The measured strength of the spin current was up to ten times higher than that obtained with previously used materials. According to the researchers, magnetic nanostructures with special combinations made up of cobalt, iron, silicon, and aluminium were particularly productive.
The experiments conducted by the Bielefeld physicists were the product of a close cooperation with the team headed by Professor Dr. Markus Münzenberg from the Ernst Moritz Arndt University in Greifswald and Professor Dr. Christian Heiliger from the Justus Liebig University in Gießen. Dr. Andy Thomas started his research on this topic at Bielefeld University and is now continuing it at the Leibniz Institute for Solid State and Materials Research in Dresden.
Source: Bielefeld University

Determinarea simultană a DTPA, EDTA și NTA prin spectrometrie vizibilă UV și HPLC(Simultaneous determination of DTPA, EDTA, and NTA by UV-visible spectrometry and HPLC )

Spectrofotometria vizibilă UV și cromatografia lichidă de înaltă performanță au fost utilizate pentru analiza simultană a agenților de chelatizare a acidului dietilenetriamin pentaacetic, a acidului etilen-diamină tetraacetic și a acidului nitrilotriacetic, ca chelați metalici în detergenții de spălare a apei,

Stimp31

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

Culorile adevarate satisfac minimizarea – Senzorul de culori stivuit(True colors meet minimization – The stacked color sensor)

Sensori de culoare sensibili la roșu, sensibili la albastru și sensibili la culoarea verde, stivuiți unul peste celălalt în loc să fie aliniați într-un model mozaic – acest principiu ar putea permite senzorilor de imagine cu rezoluție fără precedent și sensibilitate la lumină să fie creatș au dezvoltat un prototip senzor care absoarbe aproape în mod optim lumina – și este, de asemenea, ieftin să produca…

Posted: Nov 16, 2017

True colors meet minimization – The stacked color sensor

(Nanowerk News) Red-sensitive, blue-sensitive and green-sensitive color sensors stacked on top of each other instead of being lined up in a mosaic pattern – this principle could allow image sensors with unprecedented resolution and sensitivity to light to be created. However, so far, the reality hasn’t quite met expectations.
Researchers from Empa and ETH Zurich have now developed a sensor prototype that absorbs light almost optimally – and is also cheap to produce (Science, „Properties and potential optoelectronic applications of lead halide perovskites nanocrystals”).
Original image (left) and corresponding portrayal of the red, green and blue regions, and a composite image
Original image (left) and corresponding portrayal of the red, green and blue regions, and a composite image. (Image: Empa)
The human eye has three different types of sensory cells for the perception of color: cells that are respectively sensitive to red, green and blue alternate in the eye and combine their information to create an overall colored image. Image sensors, for example in mobile phone cameras, work in a similar way: blue, green and red sensors alternate in a mosaic-like pattern. Intelligent software algorithms calculate a high-resolution color image from the individual color pixels.
However, the principle also has some inherent limitations: as each individual pixel can only absorb a small part of the light spectrum that hits it, a large part of the light is lost. In addition, the sensors have basically reached the limits of miniaturization, and unwanted image disturbances can occur; these are known as color moiré effects and have to be laboriously removed from the finished image.

Transparent only for certain colors
Researchers have, therefore, been working for a number of years on the idea of stacking the three sensors instead of placing them next to each other. Of course, this requires that the sensors on top let through the light frequencies that they do not absorb to the sensors underneath. At the end of the 1990s, this type of sensor was successfully produced for the first time. It consisted of three stacked silicon layers, each of which absorbed only one color.
Stack instead of mosaic: the perovskite layers each absorb only part of the light spectrum
Stack instead of mosaic: the perovskite layers each absorb only part of the light spectrum. (Image: Empa)
This actually resulted in a commercially available image sensor. However, this was not successful on the market because the absorption spectra of the different layers were not distinct enough, so part of the green and red light was absorbed by the blue-sensitive layer. The colors, therefore, blurred and the light sensitivity was thus lower than for ordinary light sensors. In addition, the production of the absorbing silicon layers required a complex and expensive manufacturing process.
Empa researchers have now succeeded in developing a sensor prototype that circumvents these problems. It consists of three different types of perovskites – a semiconducting material that has become increasingly important during the last few years, for example in the development of new solar cells, due to its outstanding electrical properties and good optical absorption capacity (see „Further reading”). Depending on the composition of these perovskites, they can, for example, absorb part of the light spectrum, but remain transparent for the rest of the spectrum.
The researchers in Maksym Kovalenko’s group at Empa and ETH Zurich used this principle to create a color sensor with a size of just one pixel. The researchers were able to reproduce both simple one-dimensional and more realistic two-dimensional images with an extremely high color fidelity.

Accurate recognition of colors
The advantages of this new approach are clear: the absorption spectra are clearly differentiated and the color recognition is thus much more precise than with silicon. In addition, the absorption coefficients, especially for the light components with higher wavelengths (green and red), are considerably higher in the perovskites than in silicon.
As a result, the layers can be made significantly smaller, which in turn allows smaller pixel sizes. This is not crucial in the case of ordinary camera sensors; however, for other analysis technologies, such as spectroscopy, this could permit significantly higher spatial resolution. The perovskites can also be produced using a comparatively cheap process.
However, more work is still needed in order to further develop this prototype into a commercially viable image sensor. Key areas include the miniaturization of pixels and the development of methods for producing an entire matrix of such pixels in one step. According to Kovalenko, this should be possible with existing technologies.
Source: By Karin Weinmann, Empa

Noii senzori de mișcare buckypaper reprezintă un pas important spre tehnologia low-cost, de înaltă performanță care poate fi purtată(New buckypaper motion sensors a major step toward low-cost, high-performance wearable technology)

aplicațiile potențiale pentru senzorii buckypaper tipăriți sunt limitate doar de amploarea imaginației cercetătorilor. Designul cu profil redus ar putea fi integrat în foile de pat pentru a monitoriza calitatea somnului, pantofii pentru a urmări numărul de pasi și postura sau hainele de antrenament pentru a măsura intensitatea exercițiilor fizice.
Cercetătorii prevăd, de asemenea, aplicații potențiale dincolo de domeniul tehnologiei portabile. În domeniul roboticii moi, materialul ar putea facilita progresul în producerea mușchilor artificiali autocorecți responsabili.
Mai mult, senzorii scalabili reprezintă un alt pas spre viitorul mult așteptat al unui „internet al lucrurilor”, unde aproape toate computerele, dispozitivele, articolele de îmbrăcăminte, mobilierul și aparatele individuale sunt conectate digital pentru a face schimb de informații în mod liber în nor.

Posted: Nov 16, 2017

New buckypaper motion sensors a major step toward low-cost, high-performance wearable technology

(Nanowerk News) Researchers from the FAMU-FSU College of Engineering have developed a class of breakthrough motion sensors that could herald a near future of ubiquitous, fully integrated and affordable wearable technology.
In a paper published in the journal Materials and Design („Printable low-cost and flexible carbon nanotube buckypaper motion sensors”), engineers from FSU’s High-Performance Materials Institute, in collaboration with scientists from Institut National des Sciences Appliquées in Lyon, France, detail the impressive properties and cost-effective manufacturing process of an advanced series of motion sensors made using buckypaper — razor thin, flexible sheets of pure, exceptionally durable carbon nanotubes.
These new buckypaper sensors represent a marked improvement on current industry standards, with most sensors being either too crude or too inflexible to reliably monitor complex structures like the human body.
“Current technology is not designed for that,” said Richard Liang, director of the High-Performance Materials Institute and professor at the FAMU-FSU College of Engineering. “For sensor technology, you need it to be flexible, you need it to be affordable and you need it to be scalable. This new technology is versatile and the sensors are affordable to print. It’s a big innovation that presents many possibilities down the road.”
Joshua DeGraff
FAMU-FSU College of Engineering doctoral candidate Joshua DeGraff developed an advanced class of scalable motion sensors using silver ink electrodes and sheets of pure carbon nanotube buckypaper.
At this stage, potential applications for the printable buckypaper sensors are limited only by the breadth of researchers’ imaginations. The low-profile design could be integrated into bedsheets to monitor quality of sleep, shoes to track step count and posture or workout clothes to measure intensity of exercise.
Researchers also foresee potential applications beyond the realm of wearable technology. In the field of soft robotics, the material could facilitate advances in the production of responsive, self-correcting artificial muscles.
Moreover, the scalable sensors represent another step toward the long-predicted future of an “internet of things,” where virtually all of an individual’s computers, devices, garments, furniture and appliances are digitally connected to freely exchange information in the cloud.
“Most projects don’t have this many possible applications,” said doctoral candidate Joshua DeGraff, the lead author of the study. “This material could be used in structural health monitoring, wearable technology and everything in between. I’m excited because this is something that can affect a lot of people in their everyday lives.”
The novel sensor structure combines a strip of seven micron-thin buckypaper with silver ink electrodes printed from a common, commercially available ink-jet printer.
The result is a kind of perfect Goldilocks sensor: not as insensitive as common, flexible metallic sensors, but not as rigid or cumbersome as popular, more sensitive semi-conductor sensors.
The wearable buckypaper sensors are an ideal marriage of these competing qualities. They’re flexible, seamless and sensitive to subtle movements and strains.
“We measure sensors by gauge factor, which indicates how much resistance value changes as a material is strained or bent,” DeGraff said. “Our gauge factor has been up to eight times higher than commercial sensors and 75 percent higher than many other carbon nanotube sensors.”
As development of the printable sensor technology continues, researchers hope to improve upon the already remarkable thinness of the material so that it can be integrated into comfortable and non restrictive clothing. Additional testing on complex model structures is required to ensure the material’s ability to conform to the variable curves and crevices of the human body.
While the technology might not be ready for primetime quite yet, researchers are energized by its promising future.
“As engineering professors, we want to see the things we create in the lab become successful products,” Liang said. “We’re not quite there yet, but this is an important step. Consumers want great quality and affordable prices, and this material provides both of those things.”
Source: Florida State University