Autor: Liliana Decu

Cercetătorii despică câteva eșantioane de straturi de material magnetic NiPS3(Researchers cleave few-layer samples of magnetic material NiPS3)

Heterostructurile (denumite în continuare Van der Waals (VdW) atrag multă atenție datorită proprietăților lor fizice și chimice diverse. O heterostructură VdW este asamblată prin stivuirea a două sau mai multor cristale semiconductoare 2D diferite unul de celălalt . Structura este crescută prin repetarea practicii, iar stiva rezultată reprezintă un material artificial construit într-o anumită secvență, asemănător blocurilor Lego.

Posted: Mar 17, 2016

Researchers cleave few-layer samples of magnetic material NiPS3

(Nanowerk News) Heterostructures (referred to as Van der Waals (VdW) are attracting a great deal of attention due to their diverse physical and chemical properties. A VdW heterostructure is assembled by stacking two or more different 2D semiconducting crystals on top of each other. The structure is grown by repeating the practice, the resulting stack represents an artificial material constructed in a certain sequence, akin to Lego blocks.
There has been huge interest in these materials as they hold vast potential in helping science to find a new semiconductor that can replace silicon which decomposes and segregates in a natural environment.
A VdW heterostructure can overcome the limitations of 2D crystals and offer an alternative for the construction of smaller and more powerful storage devices, supercomputers, administration of medicine and enhanced memory and graphics in hand held devices.
Electrons within semiconductors roam freely and have internal states or ‘spins’. These spin currents exhibit magnetic order and can be tuned to prevent energy dissipation which occurs naturally when information is processed at vast speeds.
However, not all VdW’s have this spin state; scientifically known as an antiferromagnetic state.
Atomic structure and optical characterization_of exfoliated NiPS3
Atomic structure and optical characterization of exfoliated NiPS3.
PARK Je-Geun, a scientist from CCES, explains the unique qualities of their tested material NiPS3: “The compound nickel phosphorus trisulfide (NiPS3) is an intrinsically magnetic material and is an invaluable building block for the design for multi-layered VdW heterostructures.”
The Center is the first to obtain monolayer and multilayer samples of magnetic VdW materials; the results lay the foundation for the development of future semiconductors that are high speed, low energy consuming and highly compact.
The VdW material the IBS team experimented on belongs to a class of transition metals phosphorus trisulfides (MPS3) and, more importantly, exhibits antiferromagnetic order. With further developments, it can, theoretically, replace silicon as an ideal material for future magnetic semiconductors.
The results compiled by the IBS team have never before been reported in the form of ultrathin sheets. The team’s scientific paper, published on February 15 in Scientific Reports („Exfoliation and Raman Spectroscopic Fingerprint of Few- Layer NiPS3 Van der Waals Crystals”), outlined the potential of their work as such: “Beyond their already fascinating properties, these VdW heterostructures and superlattices may exhibit even more exotic behavior. In particular, for the design of spintronic devices, VdW materials that exhibit magnetic order would be highly desirable building blocks.”
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Raman spectra of exfoliated NiPS3.
Methods
Using the well-established Scotch tape technique, the Korean team exfoliated flakes of NiPS3 onto silicon capped by silicon oxide (SiO2). The resulting material was subjected to a heavy bombardment of high intensity lasers: a process called Raman spectroscopy, designed to provide specific information about molecular vibrations.
Other forms of atomic scanning were performed to ascertain how different the atomic make-up of NiPS3 is, in comparison, to its bulk form: MPS3. The team recorded stark differences in the Raman spectra of thin NiPS3 from the bulk material and the Raman spectra varied clearly between sheets of different layer numbers.
According to the paper these results exhibit a “key significance of our results is that bulk MPS3compounds exhibit magnetism, and antiferromagnetic ordering strongly influenced by interlayer coupling is known to take place at moderately low temperature.”
Up until now, it is quite expensive to obtain magnetic monolayer oxides materials as it requires a high-end device and the material itself is less likely to be commercially available for technical use.
This study proves that monolayer magnetic material can be obtained using magnetic atom like nickel (Ni) as well as many other magnetic atoms such as iron (Fe). The work of the IBS team is, tentatively, laying the foundations for the future study of spin-memory materials.
Research is continuously driven by our collective scientific curiosity; we are within reach of precise control of electrons and atoms which would herald a new era of scientific exploration.
The research team’s next mission is to obtain a magnetic monolayer material at moderate temperature. If they succeed, it will be very crucial step in commercializing magnetic semiconductors.
Source: Institute for Basic Science

Un material magnetic unic pentru haine de protecție(A unique magetic material for protective clothes)

au dezvoltat un material de super-rezistent pe bază de nichel si pe bază de cobalt, cu particule de ferită de stronțiu ultrafine magnetice implantate ;Experții observă o gamă largă de aplicații posibile ale materialului – de la hainele de protecție ale unui lucrător de intervenție în caz de urgență implicat în răspunsul de urgență la haina specială utilizată în industria de apărare

A unique

Perovskitul CH3NH3PbI3 bidimensional: un material optoelectronic nou promitator(

Recent, perovskitul ABX3 hibrid organic-anorganic (A = molecule organice; B = Pb 2+ sau Sn 2+ și X = Cl-, I- și / sau Br-) la proprietățile optoelectronice impresionante și performanțe ridicate în dispozitive fotovoltaice cu eficiență de conversie a puterii de peste 20%. Aceste materiale prezintă multe proprietăți interesante, cum ar fi transportul ambipolar intrinsec, coeficientul de absorbție optic ridicat, bandgap tunibil, eficiența cuantică ridicată și lungimea lungimii purtătoare a difuzorului, care prezintă potențial promițător pentru dispozitivele optoelectronice, cum ar fi celulele solare, fotodetectoarele, precum și diodele emițătoare de lumină.

Posted: Mar 16, 2016

Two-dimensional CH3NH3PbI3 perovskite: a new promising optoelectronic material

(Nanowerk News) Recently, organic-inorganic hybrid perovskites ABX3 (A=organic molecules; B=Pb2+ or Sn2+; and X=Cl-, I-, and/or Br-)) have received increasing research attention owing to their impressive optoelectronic properties and high performance in photovoltaic devices with the power conversion efficiency over 20%. These materials exhibit many interesting properties such as intrinsic ambipolar transport, high optical absorption coefficient, tunable bandgap, high quantum efficiency and long carrier diffusion length, showing promising potential for optoelectronic devices such as solar cells, photodetectors, as well as light-emitting diodes.
Perovskites CH3NH3PbX3 (X=Cl, Br, or I) can be considered as two-dimensional (2D) layered structures and they exhibit strong quantum confinements in reduced dimensions (numbers of layers). So, it is intriguing to explore the optoelectronic properties of perovskites when reducing the thickness into a few atomic layers at which they shows quantum confinement effects.
Meanwhile, the realization of 2D perovskite with controllable thickness (less than 10 nm) even single unit cell thickness will contribute to the better understanding of the intrinsic optoelectronic properties, charge carrier characters and the development of perovskite based functional devices.
A variety of methods have been developed to synthesize both colloidal as well as thin films of CH3NH3PbX3 perovskite materials from polycrystalline film to bulk single crystal. However, the introduction of defects and grain boundaries in perovskite is unavoidable, which could influence the optoelectronic properties.
Additionally, it is expected that the perovskite will exhibit unique properties after reducing it into few- or single-unit-cell thickness crystal since that the 2D quantum wells are exposed and the electronic coupling between top and bottom layers may be varied. However, an important issue need to be addressed is that perovskites can obtain different dimensionalities based on component sizes. Occupation of A sites by monovalent cations, such as CH3NH3+ and HC(NH2)2+, form a 3D framework, whereas if a larger cation, such as CH3CH2NH3+, is used, 2D or 1D structures can be obtained.
In this regard, It is extremely challenging to synthesize ultrathin 2D CH3NH3PbX3 perovskite with a thickness down to a single unit cell because of the intrinsically non-van der Waals-type 3D characteristics.
Schematic illustration of photodetector based on 2D CH3NH3PbI3
Schematic illustration of photodetector based on 2D CH3NH3PbI3.
A research team lead by Bao et al. at Soochow University demonstrated the world’s thinnest CH3NH3PbI3 perovskite nanosheets by a two-step synthesis method through the combination of solution process to produce 2D PbI2 nanosheets and vapour-phase conversion of the PbI2 to CH3NH3PbI3 nanosheets.
This research was published in ACS Nano on 24th February („Two-Dimensional CH3NH3PbI3Perovskite: Synthesis and Optoelectronic Application”).
The prepared high quality nanosheets with triangle and hexagonal shapes can be as thin as a single unit cell (~1.3 nm). They also shows tunable photoluminescence while the thickness or composition is changed. Thanks to its high quantum efficiency and excellent photoelectric properties, a high-performance photodetector was demonstrated. The device not only shows greatly enhanced photo responsivity (23 AW-1) and an ultra-fast response (< 20 ms), but also has the capability for broadband photodetection from the ultraviolet to the entire visible spectral range. Furthermore, they also experimentally demonstrated the fabrication of in-plane 2D pervoskite heterostucture, which may find interesting applications for light emission diodes.
AFM topography images of 2D CH3NH3PbI3 nanosheets with different thicknesses
(a-b) AFM topography images of 2D CH3NH3PbI3 nanosheets with different thicknesses. Scale bars: 2 µm.
This synthesis approach allows the researchers to investigate the exact correlation between the number of layers in perovskites and their optoelectronic properties. This approach could be extended to the perovskites made of different halide ions with different compositions, stated by Dr. Bao. Moreover, it will be highly important to tune the optical properties of perovskites across the whole visible spectrum.
This pioneering work on low-dimensional perovskites is an important milestone not only for the fundamental understanding of the hybrid perovskites family, but also for their new applications in optoelectronics. This work has far-ranging impact and will stimulate interest in several communities, e.g. synthesis and characterization of low-dimensional other hybrid organic-inorganic perovskites, development of perovskite-based photonics and optoelectronics with wavelength tunability, concluded

Dr. Qiaoliang Bao.
Source: Monash University

Nanoparticulele de nanoparticule ar putea conduce la utilizarea extinsă a bioplastelor în materialele de ambalare(Eggshell nanoparticles could lead to expanded use of bioplastic in packaging materials)

oamenii de știință declară că adăugarea de mici fragmente de coji de ouă la bioplastice ar putea crea un material de ambalaj biodegradabil de primă clasă care se îndoaie, dar nu se rupe ușor.unii producători produc bioplastice – o formă de plastic derivată din amidon de porumb, cartofi dulci sau alte surse regenerabile pe bază de plante – care se descompun sau se biodegradează imediat după ce se află în pământ. Cu toate acestea, majoritatea acestor materiale nu au forța și flexibilitatea necesare pentru a funcționa bine în industria ambalajelor.

Posted: Mar 15, 2016

Eggshell nanoparticles could lead to expanded use of bioplastic in packaging materials

(Nanowerk News) Eggshells are both marvels and afterthoughts. Placed on end, they are as strong as the arches supporting ancient Roman aqueducts. Yet they readily crack in the middle, and once that happens, we discard them without a second thought. But now scientists report that adding tiny shards of eggshell to bioplastic could create a first-of-its-kind biodegradable packaging material that bends but does not easily break.
The researchers present their work today at the 251st National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 12,500 presentations on a wide range of science topics.
bioplastic
Adding eggshell nanoparticles to a bioplastic (shown above) increases the strength and flexibility of the material, potentially making it more attractive for use in the packaging industry. (Image: Vijaya Rangari/Tuskegee University)
„We’re breaking eggshells down into their most minute components and then infusing them into a special blend of bioplastics that we have developed,” says Vijaya K. Rangari, Ph.D. „These nano-sized eggshell particles add strength to the material and make them far more flexible than other bioplastics on the market. We believe that these traits – along with its biodegradability in the soil – could make this eggshell bioplastic a very attractive alternative packaging material.”
Worldwide, manufacturers produce about 300 million tons of plastic annually. Almost 99 percent of it is made with crude oil and other fossil fuels. Once it is discarded, petroleum-based plastics can last for centuries without breaking down. If burned, these plastics release carbon dioxide into the atmosphere, which can contribute to global climate change.
As an alternative, some manufacturers are producing bioplastics – a form of plastic derived from cornstarch, sweet potatoes or other renewable plant-based sources – that readily decompose or biodegrade once they are in the ground. However, most of these materials lack the strength and flexibility needed to work well in the packaging industry. And that’s a problem since the vast majority of plastic is used to hold, wrap and encase products. So petroleum-based materials continue to dominate the market, particularly in grocery and other retail stores, where estimates suggest that up to a trillion plastic bags are distributed worldwide every year.
To find a solution, Rangari, graduate student Boniface Tiimob and colleagues at Tuskegee University experimented with various plastic polymers. Eventually, they latched onto a mixture of 70 percent polybutyrate adipate terephthalate (PBAT), a petroleum polymer, and 30 percent polylactic acid (PLA), a polymer derived from cornstarch. PBAT, unlike other oil-based plastic polymers, is designed to begin degrading as soon as three months after it is put into the soil.
This mixture had many of the traits that the researchers were looking for, but they wanted to further enhance the flexibility of the material. So they created nanoparticles made of eggshells. They chose eggshells, in part, because they are porous, lightweight and mainly composed of calcium carbonate, a natural compound that easily decays.
The shells were washed, ground up in polypropylene glycol and then exposed to ultrasonic waves that broke the shell fragments down into nanoparticles more than 350,000 times smaller than the diameter of a human hair. Then, in a laboratory study, they infused a small fraction of these particles, each shaped like a deck of cards, into the 70/30 mixture of PBAT and PLA. The researchers found that this addition made the mixture 700 percent more flexible than other bioplastic blends. They say this pliability could make it ideal for use in retail packaging, grocery bags and food containers – including egg cartons.
In addition to bioplastics, Rangari’s team is investigating using eggshell nanoparticles to enhance wound healing, bone regeneration and drug delivery.
Title
Nano Engineered Eggshell Toughened Polylactic Acid/Aliphatic-Aromatic Copolyester Flexible Polymer Blend
Abstract
The need for compostable alternative packaging materials is an urgent one, due to the inevitable demand in copious quantities by the increasing consumer population. Unfortunately, the mostly used polymeric materials (polypropylene and polyethylene) are recalcitrant to degradation, and contribute significantly to the concerning is of climate change. The demands for such materials have surged in commensurate proportions to match the increasing demand by growing global population. Worldwide yearly plastics production is estimated to exceed 300 million tons by 2015. Currently, the bioplastics market is surging up and capturing the plastics consumer market by a rate of 30 % annually. Hence, the development of compostable substitute plastics will immensely help in the replacement of their petroleum sourced counterparts, curtailing the complex issues related to environmental waste management and climate change. In this research, extruded compostable poly (butylene adipate-co-terephthalate) (PBAT)/agro-based polylactic acid (PLA) blend films were studied to select a suitable blend for further investigations. These blends (90/10, 80/20, 70/30, 60/40 and 50/50) were characterized using DSC, TGA, Raman spectroscopy, XRD, SEM and tensile testing. After this screening, the 70/30 blend was selected based on its desirable tensile properties and further studied by reinforcing with eggshell nanoparticles (> 30 nm by TEM analysis) engineered through mechanical attrition and ultrasound irradiation. Eggshell nanoparticles have shown great potential in tailoring of weak polymer properties toward their enhancement, at the same time the inherent egg proteins in the shells have the potential of acting as biocides (antibacterial agents) in the polymer matrix. DSC results revealed that the two polymers are immiscible, due to the presence of distinct melting points. Raman spectroscopy showed frequency vibrations and intensities unique to the individual polymers. Also, SEM microanalysis showed heterogeneous mixtures of the two matrixes with distinct phases. The tensile test showed that PLA led to improvement in tensile strength and modulus whiles PBAT significant led to enhancement in train-to-failure of the pristine blends systems. The inclusion of nano eggshell led to improvement in thermal stability, strain-to-failure and strain at maximum load of the 70/30 blend.
Source: American Chemical Society

Nanostructurile promit un impact mare asupra dispozitivelor optice cu o viteză mai mare și cu putere redusă(Nanostructures promise big impact on higher-speed, lower-power optical devices)

Nanofirele semiconductoare pot duce la avansuri în tehnologia electronică sensibilă, incluzând detectarea căldurii a senzorilor infraroșii optici și testarea biomedicală, toate putând fi încadrate în interiorul dispozitivelor electrice mici.

Posted: Mar 15, 2016

Nanostructures promise big impact on higher-speed, lower-power optical devices

(Nanowerk News) With new technology getting smaller and smaller, requiring lower power, University of Cincinnati physics research points to new robust electronic technologies using quantum nanowire structures.
The semiconductor nanowires may lead to advances in sensitive electronic technology including heat detecting optical infrared sensors and biomedical testing, all of which can fit inside small electrical devices.
Supported by multiple National Science Foundation grants, the UC research team is working with a collaborative team of physicists, electronic materials engineers and doctoral students from around the world – all to perfect the growth and development of crystalline nanowires that could form the backbone of new nanotechnologies.
But to fully apply this technology to modern devices, UC researchers are first looking closely – on a fundamental level – at how energy is distributed and measured along thin-strand nanowires so small that thousands of them could theoretically fit inside a human hair.
„Now that we know the technology can be developed, we need to understand exactly how the electrical processes work inside the nanowire cores,” say Howard Jackson and Leigh Smith, professors of physics at the University of Cincinnati. „After finally perfecting a standardized process for growing and developing crystalline nanowire fibers with our partners at the Australian National University in Canberra, we have been able to take it one step further.
„Using a combination of materials like indium gallium arsenide and indium phosphide, we can develop thin nanowire cores with protective outer shells.”
It turns out that these unique nanowire materials have unusually large spin orbit interactions, which the researchers find can conduct electricity really well and may allow the use of spin to enable new computing paradigms.
Jackson and Smith are presenting these findings at the American Physical Society Conference, in Baltimore, March 16, titled, „Exploring Dynamics and Band Structure in Mid Infrared GaAsSb and GaAsSb/InP Nanowire Heterostructures.”
SMALL YET MIGHTY
The researchers claim the secret to the success of this multi-collaborative effort is in the combination of materials used to create the nanowires. Initially grown at the Australian National University in Canberra, the nanowires are sprouted from a combination of beads of molten gold scattered across a particular surface.
As the process is heated inside a chamber using indium gallium arsenide gases, long microscopically thin core fibers sprout up from between the controlled surface environment.
Other material combinations are then introduced to form an outer shell acting as a sheath around each core, resulting in quantum nanowire semiconducting heterostructures all uniform in size, shape and behavior.
After the fibers are shipped across the globe to Cincinnati, Jackson, Smith and their team of doctoral students are then able to use sophisticated equipment to measure the electrical and photovoltaic potentials of each fiber along its surface.
In earlier research, the collaborative team found extrinsic and intrinsic problems when the fiber cores did not have the outer sheath-like shells.
„If we don’t have this outer sheath, the nanowires have a very short energy lifetime, says Jackson. „When we surround the core with this sheath, the energy lifetime can go up by an order or two orders of magnitude.”
And while gallium arsenide alone is a very common semiconductor, its energy gap is large and in the visible range, which absorbs light. To achieve success in detecting optical heat or infrared, the team says using indium gallium arsenide fibers have smaller energy gaps that can be used successfully in optical detector devices.
„The goal for one of our research equipment grants is to work with the local L3 Cincinnati Electronics Company, which makes infrared (small gap) detectors for night-vision imaging for military applications,” says Smith. „Future direct applications for this type of technology also include medical devices that detect body heat, as well as remote sensors installed in iphones that can be used for environmental purposes that detect and measure heat loss in houses.”
The researchers say this new nanowire technology is unique because it can turn different wavelengths of light into an electrical signal, and in this case it means turning an infrared light into an electric signal that can be measured.
Smith explains that with the geometry of the nanowires you can have a long axis running the length of the wire, which gives you lots of possibilities for absorption as the light comes down, but then you also have this very small diameter.
„When contacts are interspersed along either side, essentially then the electrons in the holes don’t have to travel very far before they are collected,” says Smith. „So in principle it can become a more effective detector as well as a more effective solar cell.”
SMALL DIMENSION NANOWIRES
„When you get to very small dimensions in nanowires that are small in diameter, but are a few microns long, those properties then change and can show quantum properties and become almost one-dimensional,” says Jackson. „The physics then changes as you change those sizes.”
Jackson and Smith found that the nanowire’s ultra-thin outer shells functioned best at widths of four to eight nanometers.
When looking at the overarching benefits of working with microscopic nanostructures the researchers see tremendous potential for its ability to pack much more high-energy efficiency into small devices with finite space. It’s getting closer to a win-win for everyone, they’re saying, especially when this research enters the next stage, bringing it closer to functioning inside electronic and optical sensor devices.
„Our fundamental investigation is still a step away from a direct optical device application,” says Jackson. „But you can clearly see over time that this collaborative research has made an impact.”
Source: University of Cincinnati

Straturile electronice noi acoperite cu grafenie detectează gaze nocive(New graphene-coated e-fabrics detect noxious gases)

au acoperit fire de bumbac și poliester cu un nanoglue numit albumină serică bovină (BSA). Firele au fost apoi învelite în foi de oxid de grafen.Materialele cu acoperire cu oxid de grafen redus s-au dovedit a fi deosebit de sensibile la detectarea dioxidului de azot, un gaz poluant întâlnit frecvent în evacuarea vehiculului, care rezultă și din arderea combustibililor fosili

Posted: Mar 15, 2016

New graphene-coated e-fabrics detect noxious gases

(Nanowerk News) The researchers, from the Electronics and Telecommunications Research Institute and Konkuk University in the Republic of Korea, coated cotton and polyester yarn with a nanoglue called bovine serum albumin (BSA). The yarns were then wrapped in graphene oxide sheets.
Graphene is an incredibly strong one-atom-thick layer of carbon that is known for its excellent conductive properties of heat and electricity. The graphene sheets stuck very well to the nanoglue: so much so that further testing showed the fabrics retained their electrical conducting properties after 1,000 consecutive cycles of bending and straightening and ten washing tests with various chemical detergents. Finally, the graphene oxide yarns were exposed to a chemical reduction process, which involves the gaining of electrons.
fiber sensor
The fiber sensor. (Image: Electronics and Telecommunications Research Institute)
The reduced-graphene-oxide-coated materials were found to be particularly sensitive to detecting nitrogen dioxide, a pollutant gas commonly found in vehicle exhaust that also results from fossil fuel combustion. Prolonged exposure to nitrogen dioxide can be dangerous to human health, causing many respiratory-related illnesses. Exposure of these specially-treated fabrics to nitrogen dioxide led to a change in the electrical resistance of the reduced graphene oxide.
The fabrics were so sensitive that 30 minutes of exposure to 0.25 parts per million of nitrogen dioxide (just under five times above the acceptable standard set by the U.S. Environmental Protection Agency) elicited a response. The fabrics were three times as sensitive to nitrogen dioxide in air compared to another reduced graphene oxide sensor previously prepared on a flat material.
The new technology, according to the researchers, can be immediately adopted in related industries because the coating process is a simple one, making it suitable for mass production. It would allow outdoor wearers to receive relevant information about air quality. The materials could also be incorporated with air-purifying filters to act as “smart filters” that can both detect and filter harmful gas from air.
“This sensor can bring a significant change to our daily life since it was developed with flexible and widely used fibres, unlike the gas sensors invariably developed with the existing solid substrates,” says Dr Hyung-Kun Lee, who led this research initiative. The study was published in Scientific Reports („ARTIKEL”).
Source: Electronics and Telecommunications Research Institute

Programul Squad X prevede echipe de infanterie demontate ale viitorului(Squad X Program Envisions Dismounted Infantry Squads of the Future )

Angajamentele militare moderne se desfășoară din ce în ce mai mult în condiții de câmp de luptă complexe și incerte, unde atacurile pot veni de la mai multe direcții simultan și în spectrul electromagnetic și în domenii cibernetice.PROGRAM PENTRU A DEZVOLTA SISTEME PORTABILE, INTEGRATE, care ar oferi capabilități mult îmbunătățite în domeniul fizic, electromagnetic și cibernetic

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Un material pliabil care poate schimba dimensiunea, volumul și forma (A foldable material that can change size, volume and shape )

au proiectat un nou tip de material pliabil, care este versatil, tunabil și auto-acționat. Se poate schimba dimensiunea, volumul și forma; se poate plia pentru a rezista greutatea unui elefant fără a se rupe și pentru a se pregăti pentru următoarea sarcină.

Posted: Mar 11, 2016

A foldable material that can change size, volume and shape

(Nanowerk News) Imagine a house that could fit in a backpack or a wall that could become a window with the flick of a switch.
Harvard researchers have designed a new type of foldable material that is versatile, tunable and self actuated. It can change size, volume and shape; it can fold flat to withstand the weight of an elephant without breaking, and pop right back up to prepare for the next task.
The research was lead by Katia Bertoldi, the John L. Loeb Associate Professor of the Natural Sciences at the John A. Paulson School of Engineering and Applied Sciences (SEAS), James Weaver, Senior Research Scientist at the Wyss Institute for Biologically Inspired Engineering at Harvard University and Chuck Hoberman, of the Graduate School of Design. It is described in Nature Communications.
3-D Material with Controllable Shape and Size
Harvard researchers have designed a new type of foldable material that is versatile, tunable and self actuated. Here a single cell is folds according to its actuation. (Image: Johannes Overvelde/SEAS)
„We’ve designed a three-dimensional, thin-walled structure that can be used to make foldable and reprogrammable objects of arbitrary architecture, whose shape, volume and stiffness can be dramatically altered and continuously tuned and controlled,” said Johannes T. B. Overvelde, graduate student in Bertoldi’s lab and first author of the paper.
The structure is inspired by an origami technique called snapology, and is made from extruded cubes with 24 faces and 36 edges. Like origami, the cube can be folded along its edges to change shape. The team demonstrated, both theoretically and experimentally, that the cube can be deformed into many different shapes by folding certain edges, which act like hinges. The team embedded pneumatic actuators into the structure, which can be programmed to deform specific hinges, changing the cube’s shape and size, and removing the need for external input.
The team connected 64 of these individual cells to create a 4x4x4 cube that can grow, and shrink, change its shape globally, change the orientation of its microstructure and fold completely flat. As the structure changes shape, it also changes stiffness – meaning one could make a material that’s very pliable or very stiff using the same design. These actuated changes in material properties adds a fourth dimension to the material.
„We not only understand how the material deforms, but also have an actuation approach that harnesses this understanding,” said Bertoldi. „We know exactly what we need to actuate in order to get the shape we want.”
3-D Origami Inspired Metamaterial
A self actuating folding structure is pictured. (Image: Johannes Overvelde/Harvard SEAS)
The material can be embedded with any kind of actuator, including thermal, dielectric or even water.
„The opportunities to move all of the control systems onboard combined with new actuation systems already being developed for similar origami-like structures really opens up the design space for these easily deployable transformable structures”, said Weaver.
„This structural system has fascinating implications for dynamic architecture including portable shelters, adaptive building facades and retractable roofs,” said Hoberman. „Whereas current approaches to these applications rely on standard mechanics, this technology offers unique advantages such as how it integrates surface and structure, its inherent simplicity of manufacture, and its ability to fold flat.”
„This research demonstrates a new class of foldable materials that is also completely scalable,” Overvelde said, ” It works from the nanoscale to the meter-scale and could be used to make anything from surgical stents to portable pop-up domes for disaster relief.”
Source: Harvard John A. Paulson School of Engineering and Applied Sciences

Read more: A foldable material that can change size, volume and shape

Design nou al celulelor de combustibil alimentat cu nanocristale învelite în grafen ( New fuel cell design powered by graphene-wrapped nanocrystals )

au elaborat o nouă rețetă de materiale pentru baterii pile de combustie cu hidrogen – care înconjoară nanocristalele de magneziu absorbante de hidrogen cu foi grafenice atomice subțiri – pentru a-și împinge performanțele înainte în zonele cheie.
Grafenul protejează nanocristalele de oxigen, umiditate și contaminanți, în timp ce găurile naturale mici permit moleculelor de hidrogen mai mici să treacă. Acest proces de filtrare depășește problemele comune care degradează performanța hidrurilor metalice pentru stocarea de hidrogen. Într-un vehicul alimentat cu celule de combustie pe bază de hidrogen, care utilizează aceste materiale, cunoscut sub numele de „hidrură metalică legată cu metal”, gazul hidrogen pompat într-un vehicul ar fi absorbit chimic de pulberea de nanocristalină de magneziu și ar fi asigurat în condiții de presiune scăzută .

Posted: Mar 11, 2016

New fuel cell design powered by graphene-wrapped nanocrystals

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

Read more: New fuel cell design powered by graphene-wrapped nanocrystals