Categorie: Materiale noi cu structura compozita

Graphene la toast, oricine? (W / video)(Graphene on toast, anyone? (w/video))

investighează modalitățile de a scrie modele de grafen în produsele alimentare și în alte materiale pentru a încorpora rapid etichetele și senzorii conductivi de identificare în produsele în sine.separată pe mâncare, ci pe mâncarea în sine”.
Multi pași laser cu un fascicul defocalizat au permis cercetătorilor să scrie modelele LIG în pânză, hârtie, cartofi, coji de nucă de cocos și plută, precum și toast. (Pâinea este prăjită mai întâi pentru a „carboniza” suprafața.) Procesul se întâmplă în aer la temperaturi ambiante.
„În unele cazuri, lexarea multiplă creează o reacție în două etape”, a spus Tour. In primul rand, laserul transforma fototeramatic suprafata tinta in carbon amorf. Apoi, pe trecerea ulterioara a laserului, absorbtia selectiva a luminii infrarosii transforma carbonul amorf in LIG, descoperind ca lungimea de unda are importanta.Acest lucru are aplicații pentru a pune urme conductive pe îmbrăcăminte, indiferent dacă doriți să încălziți îmbrăcămintea sau să adăugați un senzor sau un model conductiv”,

Posted: Feb 13, 2018

Graphene on toast, anyone? (w/video)

(Nanowerk News) Rice University scientists who introduced laser-induced graphene (LIG) have enhanced their technique to produce what may become a new class of edible electronics.
The Rice lab of chemist James Tour, which once turned Girl Scout cookies into graphene, is investigating ways to write graphene patterns onto food and other materials to quickly embed conductive identification tags and sensors into the products themselves.
„This is not ink,” Tour said. „This is taking the material itself and converting it into graphene.”
text
Laser-induced graphene is a highly conductive addition to a piece of bread. A Rice University lab is using an industrial laser to write graphene patterns on everyday objects, including food, cloth, cardboard and wood. (Image: Jeff Fitlow/Rice University)
The process is an extension of the Tour lab’s contention that anything with the proper carbon content can be turned into graphene. In recent years, the lab has developed and expanded upon its method to make graphene foam by using a commercial laser to transform the top layer of an inexpensive polymer film.
The foam consists of microscopic, cross-linked flakes of graphene, the two-dimensional form of carbon. LIG can be written into target materials in patterns and used as a supercapacitor, an electrocatalyst for fuel cells, radio-frequency identification (RFID) antennas and biological sensors, among other potential applications.
The new work reported in the American Chemical Society journal ACS Nano(DOI:10.1021/acsnano.7b08539″) demonstrated that laser-induced graphene can be burned into paper, cardboard, cloth, coal and certain foods, even toast.
„Very often, we don’t see the advantage of something until we make it available,” Tour said. „Perhaps all food will have a tiny RFID tag that gives you information about where it’s been, how long it’s been stored, its country and city of origin and the path it took to get to your table.” He said LIG tags could also be sensors that detect E. coli or other microorganisms on food. „They could light up and give you a signal that you don’t want to eat this,” Tour said. „All that could be placed not on a separate tag on the food, but on the food itself.”
Multiple laser passes with a defocused beam allowed the researchers to write LIG patterns into cloth, paper, potatoes, coconut shells and cork, as well as toast. (The bread is toasted first to „carbonize” the surface.) The process happens in air at ambient temperatures.
„In some cases, multiple lasing creates a two-step reaction,” Tour said. „First, the laser photothermally converts the target surface into amorphous carbon. Then on subsequent passes of the laser, the selective absorption of infrared light turns the amorphous carbon into LIG. We discovered that the wavelength clearly matters.”
The researchers turned to multiple lasing and defocusing when they discovered that simply turning up the laser’s power didn’t make better graphene on a coconut or other organic materials. But adjusting the process allowed them to make a micro supercapacitor in the shape of a Rice „R” on their twice-lased coconut skin.
Defocusing the laser sped the process for many materials as the wider beam allowed each spot on a target to be lased many times in a single raster scan. That also allowed for fine control over the product, Tour said. Defocusing allowed them to turn previously unsuitable polyetherimide into LIG.
„We also found we could take bread or paper or cloth and add fire retardant to them to promote the formation of amorphous carbon,” said Rice graduate student Yieu Chyan, co-lead author of the paper. „Now we’re able to take all these materials and convert them directly in air without requiring a controlled atmosphere box or more complicated methods.”
The common element of all the targeted materials appears to be lignin, Tour said. An earlier study relied on lignin, a complex organic polymer that forms rigid cell walls, as a carbon precursor to burn LIG in oven-dried wood. Cork, coconut shells and potato skins have even higher lignin content, which made it easier to convert them to graphene.
Tour said flexible, wearable electronics may be an early market for the technique. „This has applications to put conductive traces on clothing, whether you want to heat the clothing or add a sensor or conductive pattern,” he said.
Source: By Mike Williams, Rice University

Compozit-piezoelectric de cea mai înaltă calitate de astăzi(Today’s highest quality composite-piezoelectric)

au reușit să dezvolte un material compozit care are astăzi cele mai bune proprietăți piezoelectrice.Piezoelectrica este unul dintre cele mai uimitoare materiale din lume.Materialele compozite bazate pe polimeri și feroelectrice clasice, care au proprietăți piezo- și piroelectrice, au un număr de avantaje în comparație cu ceramica pură: densitatea, capacitatea de a produce părți de orice dimensiune și formă, elasticitatea mecanică, stabilitatea proprietăților electrofizice și simplitatea și costul relativ scăzut al producției. În plus, compozitul sintetizat sa dovedit a fi excelent la presiuni ridicate, ceea ce îl face o bază excelentă pentru senzori de presiune „.

Posted: Feb 12, 2018

Today’s highest quality composite-piezoelectric

(Nanowerk News) NUST MISIS scientists jointly with an international group of scientists have managed to develop a composite material that has the best piezoelectric properties today. The research results were published in Scientific Reports („Evolution of poled state in P(VDF-TrFE)/(Pb,Ba)(Zr,Ti)O3 composites probed by temperature dependent Piezoresponse and Kelvin Probe Force Microscopy”).
Piezoelectrics are one of the world`s most amazing materials. It is possible to literally squeeze electricity from them. That is, an electric charge appears at the time of the material`s compression (or stretching). This is called the piezoelectric effect. Piezoelectric materials can be applied in many fields – from pressure sensors and sensitive elements of a microphone to the controller ink pressing in ink-jet printers and quartz resonators.
Composite-Piezoelectric
Topography (a), PFM images of a pristine state (b) and after poling by +/ 60V (c). (Image: NUST MISIS)
Lead zirconate titanate is one of the most popular piezoelectric materials. However, it has several disadvantages: it is heavy and inflexible. Additionally, lead production often causes great harm to the environment. That is why scientists are constantly looking for new materials with low lead content as well as with less weight and greater flexibility. In particular, the creation of flexible piezoelectric materials (while maintaining the key properties) would greatly expand piezoelectric materials` possibilities both as acoustic membrane and as pressure sensors.
An international team of scientists from the University of Duisburg-Essen (Germany), NUST MISIS, National Research Tomsk State University and the National Research University of Electronic Technology, working with the financial support of the Russian Science Foundation (grant 16-19-10112), has managed to create such a material and analyze its properties. For this, the nanoparticles consisting of titanate-zicronate barium-lead were placed in a complex polymer consisting of vinylidene disluoride and trifluoroethylene. By diversifying the composition of the components, scientists were able to get the most ideal composite.
„The Russian-German group of scientists, including Dmitri Kiselev, a Senior Researcher at the NUST MISIS R&D Center for Materials Science & Metallurgy, has managed to create a composite material based on ceramics and organic polymer whose properties exceed today`s best piezoelectric materials. The research’s experimental part was carried out with an atomic-force microscope in the University of Duisburg-Essen (Germany). Thanks to this scientific collaboration, Dmitri Kiselev has gained skills from the world`s best scanning probe microscope, which he can later apply at NUST MISIS”, said Alevtina Chernikova, Rector of NUST MISIS.
According to Dmitri Kiselev, the developed material has a very distinct field of application due to its polymer component: „Composite materials based on polymer and classic ferroelectrics, which have piezo- and pyroelectric properties, have a number of advantages compared to pure ceramics: low density, the ability to manufacture parts of any size and shape, mechanical elasticity, stability of electrophysical properties, and the simplicity and relatively low cost of production. Additionally, the synthesized composite has proved to be excellent at high pressures which makes it an excellent base for pressure sensors”.
According to Kiselev, to study the composite they had to modify the standard technique which allowed them to correctly visualize the nanoparticles of ceramics in the volume of the polymer matrix: „In order to capture the electrical signal more clearly, we heated our sample in a certain way from room temperature to 60 degrees Celsius. It allowed us to measure the material’s characteristics very qualitatively and reproducibly. Our method will greatly simplify the work of our colleagues in the study of composites, so I hope that it will be in demand among our colleagues microscopists”.
Source: National University of Science and Technology MISIS

Putine straturi de telur ca succesor promitator al fosforului negru(Few-layer tellurium as a promising successor of black phosphorus)

Acest material reușește majoritatea proprietăților izbitoare ale BP și, în plus, oferă o stabilitate mai bună a mediului, un cost de fabricație mult mai mic (cu metode de chimie umedă) și o absorbție mai puternică a luminii decât cele ale BP. În acest scenariu, FL-α-Te ar putea fi considerat un succesor superior al BP.

Posted: Feb 09, 2018

Few-layer tellurium as a promising successor of black phosphorus

(Nanowerk News) Two-dimensional (2D) layered materials have received considerable attention because of their potential applications in various fields since the experimental discovery of graphene.
Two-dimensional elementary semiconductors are particularly desired owing to their superior features in terms of fabrication, purification and doping.
Few-layer black phosphorus (BP) is the first 2D mono-elementary semiconductor showing high electronic carrier mobility, strong optical absorption, linear dichroism, promising figure of merit and high tunability with external fields. All the properties immediately put few-layer BP under spotlights since its discovery in 2014.
However, the flawed air-stability and difficulties in largescale fabrication were found to be two remaining issues that obscure practical applications of few-layer BP in the industry. People thus get started to question if a promising or even superior successor of BP exists. The target semiconductor is preferably an elementary one. It should also allow low-cost and large-scale synthesis and offer good environmental stability without sacrificing those striking properties offered by BP.
Professor Wei Ji has led a research group at Renmin University of China to theoretically model surfaces and interfaces of emerging electronic materials and to predict physical properties of devices comprised of these materials.
Recently, they collaborated with Prof. Yang Chai from the Hong Kong Polytechnic University to report a theoretical study of a novel chain-like 2D-material, namely few-layer α-Tellurium (FL-α-Te), and predicted this material to have extremely high carrier mobility with a layer-tunable bandgap, strong light absorption, mixing of vibrational modes, layer-dependent energy maps of valence and conduction bands and among other striking properties („Few-layer Tellurium: one-dimensional-like layered elementary semiconductor with striking physical properties”).
few-layer alpha-Tellurium
A chain-like two-dimensional material, few-layer alpha-Tellurium, has intrinsically geometric anisotropy, anisotropic inter-chain (-layer) vibrational behaviors, higher mobility along the non-covalent bonding direction and isotropic light absorption, as governed by the found covalent-like quasi-bonding for the inter-chain (-layer) interactions. (© Science China Press) (click on image to enlarge)
The FL-α-Te is a representative material of layered one-dimensional materials, which are a novel and fast developing category of 2D-materials. They first examined the stability of three likely few-layer phases using state-of-the-art density functional theory calculations.
Their calculation shows α-Tellurium is the most stable phase for bilayer and thicker layers. Given the stability unveiled, they found that a covalent-like quasi-bonding (CLQB) dominates the inter-chain interaction in both intra- and inter-layer directions. This CLQB is in analogy to the found interlayer interactions in BP, PtS2 or PtSe2, in which it shows wavefunction hybridization but does not provide extra energy gain.
They managed to correlate this bonding with the layer-dependent geometric and electronic structures and their resulting behaviors in terms of electric, optical, and vibrational properties.
Few-layer α-Te has extremely high hole-mobility up 105 cm2/Vs exceptionally along the non-covalent-bound (CLQB) direction and 103 cm2/Vs for the covalent-bound direction, tunable bandgap from 0.31 eV (Bulk) to 1.17 eV (2L), anisotropic inter-chain (-layer) vibrational behaviors, a crossover of interlayer shear and breathing force constants, large ideal strength (over 20%) and nearly isotropic strong light absorption (up to 9% per layer) from a highly anisotropic geometry.
They also found, specifically in few-layer α-Te, that the energy surfaces of both valence and conduction bands substantially develop from bulk to bilayer, exhibiting an „M-like” line profile of the hole pocket, which was usually found in topological insulators and is ideal for thermoelectrics.
This material succeeds most of the striking properties of BP and additionally offers a better environmental stability, a much lower fabrication cost (with wet-chemistry methods) and a stronger light absorption than those of BP. In this scenario, FL-α-Te could be regarded as a superior successor of BP.
The extraordinarily high carrier mobility revealed in the CLQB direction conceptually updates the understanding of the role of non-covalent interactions in carrier mobility and may open a new avenue for seeking high carrier mobility materials.
Source: Science China Press

Aplicat în nanoparticule deformate în apă și aplicația sa pentru moartea celulelor induse de fotografie(Water-soluble warped nanographene and its application for photo-induced cell death)

Nanographene are grila hexagonală de carbon din grafen, dar constă doar din câteva inele de carbon cu proprietăți electronice reglabile. Una dintre problemele sale majore care împiedică aplicarea pe scară largă a dispozitivelor optoelectronice sau a biomedicinei este insolubilitatea sa. Prin urmare, pentru a suprima stivuirea și agregarea, s-a sintetizat un nou tip de nanograf cu o structură îndoită, așa-numitul nanographene deformat.

Posted: Feb 09, 2018

Water-soluble warped nanographene and its application for photo-induced cell death

(Nanowerk News) Graphene and its nano-sized little sibling, nanographene, are well known for their remarkable photoelectronic properties. However, biomedical applications are hampered by the insolubility of the materials, especially in water.
A Japanese team of scientists has now introduced substituted “warped nanographene,” which is soluble in a broad range of solvents while maintaining its photophysical properties. In their publication in Angewandte Chemie („A Water-Soluble Warped Nanographene: Synthesis and Applications for Photoinduced Cell Death”), the authors also emphasize its photodynamic potential to selectively kill cells upon irradiation.
Water-Soluble Warped Nanographene
Water-Soluble Warped Nanographene – Synthesis of a water-soluble warped nanographene and its application for photo-induced cell death. (© Wiley-VCH)
Nanographene has the hexagonal carbon lattice of graphene but consists of only a few carbon rings with tunable electronic properties. One of its big issues hampering widespread application in optoelectronic devices or biomedicine is its insolubility. Therefore, to suppress stacking and aggregation, a new type of nanographene with a bended structure has been synthesized, the so-called warped nanographene.
Kenichiro Itami at Nagoya University, Japan, and his colleagues have now found a way to furnish the warped nanographene even further to obtain a fully soluble, amphiphilic product. The new structure was biocompatible, but upon irradiation it killed its host cell. This effective photosensitization behavior could inspire future research in photodynamic cancer therapy, the authors believe.
The poor solubility of graphene-like materials has been regarded problematic since the discovery of graphene as an intriguing one-layer carbon modification in 2004. To improve solubility, Itami and his colleagues have developed warped nanographene molecules with chemical substituents at the outer rim of the aromatic structure.
The substituents were introduced by the relatively simple and powerful strategy of borylation. Once the molecule is borylated, the boron substituent can be replaced by other substituents, in this case, by an aromatic molecule bearing highly soluble tetra(ethylene glycol) chains (TEG).
Applying this substitution–replacement strategy twice, the scientists accomplished the synthesis of a warped, i.e., bended, nanographene molecule that was stable in a broad range of solvents including water. Excited with a laser, it exhibited green fluorescence.
This fluorescence points to applications in biology, for example, as a dye in bioimaging. A further application came rather unexpected, the scientists reported. Upon excitation, the molecule, which was otherwise not harmful to the cells, killed the cell population of the human HeLa cell line to almost 100 percent.
The authors proposed: “Although the mechanism is unclear, the relatively high efficiency of the singlet oxygen generation of [the soluble warped nanographene] may contribute to its HeLa cell death.” Thus, a mechanism similar to dye sensitization and production of reactive oxygen species can be assumed.
These second-generation nanographenes combine the remarkable optoelectronic properties of graphene with biocompatibility. They may well play a future role in bioimaging, photodynamic therapy, and similar applications.
Source: Wiley

Stivuirea pe grafen(Stacking on the graphene)

Cercetătorii din Japonia au găsit o modalitate de a forma două materiale, fiecare realizat din trei straturi de grafen. Ghepena fiecărui material este stivuită diferit și are proprietăți electrice unice. Munca lor are implicații pentru dezvoltarea unor noi dispozitive electronice, cum ar fi senzorii foto care convertesc lumina în energie electrică.

Posted: Feb 09, 2018

Stacking on the graphene

(Nanowerk News) Researchers in Japan have found a way to form two materials, each made of three layers of graphene. Each material’s graphene is stacked differently and has unique electrical properties. Their work has implications for the development of novel electronic devices, such as photo sensors that convert light into electrical energy.
In 2004, two scientists realized they had isolated a single layer of carbon atoms on a scotch tape used to clean a graphite crystal. Since then, graphene has captured the imagination of researchers due to its fascinating properties: it is 200 times stronger than steel, is very flexible, and it is an excellent conductor of electricity.
Graphene’s carbon atoms are arranged into hexagons, forming a honeycomb-like lattice. Placing one layer of graphene on top of another leads to the formation of bilayer graphene. The layers can be arranged in one of two positions: the centres of the carbon hexagons of each layer can be organized immediately above one another, called AA-stacking, or they can be displaced forwards so that a hexagon centre in one layer is above a carbon atom below it, called AB-stacking. AB-stacking of two layers of graphene leads to the formation of a material with semiconducting properties by applying an external electric field.
The schematic crystal structures of (a) ABA- and (b) ABC- stacked three layer graphene
The schematic crystal structures of (a) ABA- and (b) ABC- stacked three layer graphene. (Image: Katsuaki Sugawara)
Deliberately stacking three layers of graphene has proven difficult. But doing so could help researchers study how the physical properties of tri-layered materials change based on how the layers are stacked. This could lead to the development of novel electrical devices.
Researchers at Japan’s Tohoku University and Nagoya University have now fabricated two different types of trilayer graphene with different electrical properties.
They heated silicon carbide using one of two methods. In one experiment, silicon carbide was heated to 1,510°C under pressurized argon. In another, it was heated to 1,300°C in a high vacuum. Both materials were then sprayed with hydrogen gas in which the bonds were broken to form single hydrogen atoms. Two types of trilayer graphene then formed. The silicon carbide heated under pressurized argon formed into ABA-stacked graphene, in which the hexagons of the top and bottom layers were exactly aligned while the middle layer was slightly displaced. The silicon carbide heated in a vacuum developed into ABC-stacked graphene, in which each layer was slightly displaced in front of the one below it.
The researchers then examined the physical properties of each material and found that their electrons behaved differently.
The ABA graphene was an excellent electrical conductor, similar to monolayer grapheme. The ABC grapheme, on the other hand, acts more like AB graphene in that it had semi-conductor properties.
„The present success in selective fabrication of ABA and ABC trilayer graphene would widen the feasibility of graphene-based nano-electronic devices with variable layer numbers and stacking sequences,” conclude the researchers in their study published in the journal NPG Asia Materials(„Selective fabrication of free-standing ABA and ABC trilayer graphene with/without Dirac-cone energy bands”).
Source: Tohoku University

Metasuprafețele permit o performanță îmbunătățită a obiectivelor optice(Metasurfaces enable improved optical lens performance)

Obiectivele lentile apochromatice – cele care focalizează în mod corespunzător cele trei culori roșu, albastru și verde – care au o curbură mai mică și sunt mai subțiri și mai ușoare ar putea îmbunătăți camerele telefonului mobil și permit fabricarea de telefoane celulare mai subțiri. De asemenea, acestea ar putea face camere mai ușoare, mai bune pentru corp, camere pentru cască, zone de lunetist, dispozitive de imagistică termică și vehicule aeriene fără pilot sau dronuri. În esență, orice lucru care folosește lentile pentru imagine poate fi simplificat și mai ușor.

Posted: Feb 09, 2018

Metasurfaces enable improved optical lens performance

(Nanowerk News) Producing the perfect color images we need and love often requires multiple, heavy lenses so that each color focuses in exactly the same plane. Now Penn State engineers have developed a new theory that solves the problem using a single thin lens comprised of gradient index materials and metasurface layers to properly direct the light.
„If we want high performance optical systems, then we have to overcome material dispersion,” said Sawyer D. Campbell, assistant research professor in electrical engineering. „If we don’t, we get smeary colors, which significantly degrades image quality.”
Single apochromatic lenses – ones that properly focus the three colors red, blue and green – that have less curvature and are thinner and lighter could improve cell phone cameras and allow manufacture of thinner cell phones. They also could make lighter, better body cameras, helmet cameras, sniper scopes, thermal imaging devices and unmanned aerial vehicles or drones. In essence, anything that uses lenses to image could be made simpler and lighter.
„Usually there are several lenses, but that increases the weight,” said Jogender Nagar, graduate student in electrical engineering. „Our aim is to improve SWaP – reduce size and weight while increasing performance.”
The researchers thought to combine two technologies: that of gradient-index (GRIN) lens, and metasurfaces – ultra-thin optical layers with sub-wavelength features that manipulate the wavefront in a desired manner. The researchers report the results of their work in the current issue of Optica („Multi-element, multi-frequency lens transformations enabled by optical wavefront matching”).
focussing light through lenses
Traditional glass lenses (a) focus different colors to different points resulting in color separation and image blurring. In contrast, newly developed metasurface-augmented gradient-index lenses (b) correct for color separation by focusing blue, green, and red light to the same point. (Image: Jogender Nagar, Penn State)
„Our system uses one lens,” said Nagar. „We use the curvature of the lens, the distribution of materials in the lens, and a metasurface – a pattern placed on the surface – to make the lens thinner, lighter, but still focus properly.”
Most lenses use curvature to control the focal point, but three separate conventional lenses are needed to focus the three separate colors to one focal point and produce a high quality image. By spatially varying the material composition inside the lens, one GRIN lens can perfectly focus two colors. Then, by adding a metasurface to the GRIN lens, one layered lens can perfectly focus all three colors and do the work of three conventional lenses.
„The gradient in the lens can be axial – varying along the direction of light propagation, or optical axis; or radial – varying outwardly from the optical axis,” said Douglas H. Werner, John L. and Genevieve H. McCain Chair Professor in electrical engineering. „Or it could be more complex.”
The researchers developed a theoretical model and simulation framework for creating these lenses.
„We had to use some advanced tools that were specially developed in the lab,” said Werner. „Tools for modeling, simulation and optimization that we created for solving such a challenging design problem.”
The theoretical model specifies the proper surface curvature and gradient in the GRIN lens and the proper patterning for the metasurface to satisfy the requirements of perfect focusing of all three colors. The model optimizes both the lens and the metasurface to work together.
„The theory is very general and covers a wide range of conditions,” said Werner. „Fabrication will be the challenge initially. We hope development of the theory will steer the fabrication, making it possible to produce such lenses at a low cost and high volume.”
Source: Penn State

Super lemnul ar putea înlocui oțelul(Super wood could replace steel)

au gasit o modalitate de a face lemnul de peste 10 ori mai puternic si mai dur decat inainte, creand o substanta naturala mai puternica decat multe aliaje de titan.
„Acest nou mod de a trata lemnul îl face de 12 ori mai puternic decât lemnul natural și de 10 ori mai dur”.Acest lucru ar putea fi un concurent pentru oțel sau chiar aliaje de titan, este atât de puternic și durabil. Este de asemenea comparabil cu fibra de carbon, dar mult mai puțin costisitor”

Posted: Feb 07, 2018

Super wood could replace steel

(Nanowerk News) Engineers at the University of Maryland, College Park (UMD) have found a way to make wood more than 10 times times stronger and tougher than before, creating a natural substance that is stronger than many titanium alloys.
„This new way to treat wood makes it 12 times stronger than natural wood and 10 times tougher,” said Liangbing Hu of UMD’s A. James Clark School of Engineering and the leader of the team that did the research, to be published on February 8, 2018 in the journal Nature(„Processing bulk natural wood into a high-performance structural material”).
Liangbing Hu and Teng Li, University of Maryland
Liangbing Hu, left, and Teng Li, right, are engineers at the University of Maryland, College Park who have found a way to make wood more than 10 times stronger and tougher than before. (Image: University of Maryland)
„This could be a competitor to steel or even titanium alloys, it is so strong and durable. It’s also comparable to carbon fiber, but much less expensive.” Hu is an associate professor of materials science and engineering and a member of the Maryland Energy Innovation Institute.
„It is both strong and tough, which is a combination not usually found in nature,” said Teng Li, the co-leader of the team and Samuel P. Langley Associate Professor of mechanical engineering at UMD’s Clark School. His team measured the dense wood’s mechanical properties. „It is as strong as steel, but six times lighter. It takes 10 times more energy to fracture than natural wood. It can even be bent and molded at the beginning of the process.”
The team also tested the new wood material and natural wood by shooting bullet-like projectiles at it. The projectile blew straight through the natural wood. The fully treated wood stopped the projectile partway through.
„Soft woods like pine or balsa, which grow fast and are more environmentally friendly, could replace slower-growing but denser woods like teak in furniture or buildings,” Hu said.
„The paper provides a highly promising route to the design of lightweight, high performance structural materials, with tremendous potential for a broad range of applications where high strength, large toughness and superior ballistic resistance are desired, ” said Huajian Gao, a professor at Brown University who was not involved in the study. „It is particularly exciting to note that the method is versatile for various species of wood and fairly easy to implement.”
„This kind of wood could be used in cars, airplanes, buildings – any application where steel is used,” Hu said.
„The two-step process reported in this paper achieves exceptionally high strength, much beyond what [is] reported in the literature,” said Zhigang Suo, a professor of mechanics and materials at Harvard University, also not involved with the study. „Given the abundance of wood, as well as other cellulose-rich plants, this paper inspires imagination.”
„The most outstanding observation, in my view, is the existence of a limiting concentration of lignin, the glue between wood cells, to maximize the mechanical performance of the densified wood. Too little or too much removal lower the strength compared to a maximum value achieved at intermediate or partial lignin removal. This reveals the subtle balance between hydrogen bonding and the adhesion imparted by such polyphenolic compound. Moreover, of outstanding interest, is the fact that that wood densification leads to both, increased strength and toughness, two properties that usually offset each other,” said Orlando J. Rojas, a professor at Aalto University in Finland.
Hu’s research has explored the capacities of wood’s natural nanotechnology. They previously made a range of emerging technologies out of nanocellulose related materials: (1) super clear paper for replacing plastic; (2) photonic paper for improving solar cell efficiency by 30%; (3) a battery and a supercapacitor out of wood; (4) a battery from a leaf; (5) transparent wood for energy efficient buildings; (6) solar water desalination for drinking and specifically filtering out toxic dyes. These wood-based emerging technologies are being commercialized through a UMD spinoff company, Inventwood LLC.
Source: American Chemical Society

Progrese în fabricarea diamantelor nanocristaline pentru studierea materialelor în condiții extreme(Advances in fabricating nanocrystalline diamonds to study materials under extreme conditions)

Diamantele nanocristaline arata ca un mic nubbin de material cultivat pe partea superioara a suprafetei cutelui plat dintr-un diamant de bijuterie de oa treia carate. Pentru a construi nubina, diamantul bijuteriei este acoperit cu o peliculă subțire de tungsten care are un cerc de 15 până la 20 de micrometri gravat în centru. Diamantul nanocristalina incepe sa creasca ca si boabe de diamante mici in acel cerc deasupra suprafetei diamantelor bijuterie. Granulele se formează prin depunerea de vapori din plasmă, obținută prin încălzirea gazelor de metan, hidrogen și azot

Posted: Feb 06, 2018

Advances in fabricating nanocrystalline diamonds to study materials under extreme conditions

(Nanowerk News) Using a nanocrystalline diamond built by plasma vapor deposition, Yogesh Vohra, Ph.D., has already produced a pressure nearly two times greater than that found at the center of the Earth.
Now he reports, in a study published in Scientific Reports („Rapid Growth of Nanocrystalline Diamond on Single Crystal Diamond for Studies on Materials under Extreme Conditions”), that the manufacturing process of these novel, nanocrystalline-diamond micro-anvils has proved to be “remarkably consistent” and demonstrates “a high level of reproducibility in fabrication.”
Single-crystal gem diamond sits on microscope under laser light
Single-crystal gem diamond sits on microscope under laser light. (Image: University of Alabama at Birmingham)
These results are encouraging for continued research to study materials under extreme conditions of pressure and temperature, says Vohra, a professor and university scholar of physics in the UAB College of Arts and Sciences at the University of Alabama at Birmingham.
The nanocrystalline diamond looks like a tiny nubbin of material grown on top of the flat culet surface of a one-third-carat gem diamond. To construct the nubbin, the gem diamond is coated with a tungsten thin film that has a 15- to 20-micrometer circle etched out at the center. The nanocrystalline diamond begins to grow as tiny diamond grains in that circle on top of the gem diamond surface. The grains form through vapor deposition from plasma made by heating methane, hydrogen and nitrogen gases
Plasma is a hot, ionized gaseous substance that is the fourth state of matter after liquids, solids and gasses. Grains of nanocrystalline diamond are typically between 5 and 100 nanometers in size.
Vohra and UAB colleagues looked at early-stage nucleation morphologies of the nanocrystals at one, three and 15 minutes after start of synthesis. They found that nucleation of nanocrystalline diamonds begins rapidly, and without need of pre-growth surface seeding with tiny specks of diamond. In contrast, such a seeding is required for diamond growth on some other surfaces.
After only one minute of growth, electron microscope images showed substantial nucleation sites on the surface of the single-crystal gem diamond anvil. At three minutes, only small areas of the gem surface lacked nanocrystalline diamond coverage, and by 15 minutes, there was complete and uniform coverage by nanocrystalline grains that begin to clump together over the entire growth region.
Growth slowed between three and six hours, and the nanocrystalline diamond tended to coalesce into a hemi-spherical structure. Vohra says this geometry has been observed consistently over every two-stage growth experiment the UAB researchers have performed. In addition, there seems to be a geometrical limit to the total dimensions of growth.
nanocrystalline diamond
This nubbin on the flat surface of a gem diamond (top) is a nanocrystalline diamond, half the width of an average human hair. Higher magnification (bottom) shows the granular structure of the nanocrystalline diamond. (Image: University of Alabama at Birmingham)
The nanocrystalline nubbin greatly enhances the pressures achievable with diamond micro-anvils. Single-crystal gem diamonds with a culet size of 300 microns, without the nanocrystalline nubbin, can generate only 75 gigapascals of pressure. When the nanocrystalline diamond is added, the micro-anvils can generate as much as 500 gigapascals of pressure. The UAB researchers hope to reach a pressure of 1,000 gigapascals, or one terapascal, of pressure with their nanocrystalline diamond micro-anvils. That is close to the pressure at the center of the planet Saturn.
This immense pressure can potentially create as yet unknown new materials and are also utilized to study phase changes and compression behavior of materials. In the natural world, such immense forces deep underground can turn carbon into diamonds, or volcanic ash into slate.
The UAB team also examined nanocrystalline diamond micro-anvils that showed detachment during the compression and decompression in a diamond-anvil cell device. Using electron force microscopy, scanning electron microscopy and Raman spectroscopy, the researchers found that the detachment failure occurred in the bulk of the single-crystal gem diamond anvil below the culet surface, not at the interface between the gem diamond and the nanocrystalline diamond nubbin.
This indicated that the interfacial adhesive strength between the gem diamond and the nanocrystalline diamond nubbin appears to be substantial, and that the interface can survive ultrahigh shear stresses.
Vohra says UAB researchers will continue studies to manipulate grain size and the adhesive strength at the interface to optimize nanocrystalline diamond micro-anvils for high-pressure research.
Besides Vohra, authors of the paper “Rapid growth of nanocrystalline diamond on single crystal diamond for studies on materials under extreme conditions” are Samuel L. Moore, Gopi K. Samudrala and Shane A. Catledge, UAB Department of Physics.
Source: University of Alabama at Birmingham

Cercetătorii descoperă un material excepțional de catod din baterii de metal de magneziu(Researchers discover an exceptional metal-oxide magnesium battery cathode material)

a descoperit un material catodic de metal de magneziu excepțional de metal de metale, cercetătorii mutând un pas mai aproape de livrarea bateriilor care promite o densitate mai mare de stocare a energiei, avansuri în ceea ce privește siguranța, costul și performanța în comparație cu omologii lor ubiquitous litiu-ion (Li-ion). bateriile ar fi mai puțin costisitoare, mai ușoare și mai sigure pentru a permite adoptarea mai ușoară a formatelor de dimensiuni mari necesare vehiculelor electrice și pentru a stoca energia generată de soarele și sursele eoliene.

Posted: Feb 06, 2018

Researchers discover an exceptional metal-oxide magnesium battery cathode material

(Nanowerk News) A multi-institution team of scientists led by Texas A&M University chemist Sarbajit Banerjee has discovered an exceptional metal-oxide magnesium battery cathode material, moving researchers one step closer to delivering batteries that promise higher density of energy storage on top of transformative advances in safety, cost and performance in comparison to their ubiquitous lithium-ion (Li-ion) counterparts.
„The worldwide push to advance renewable energy is limited by the availability of energy storage vectors,” says Banerjee in the team’s paper, published in the journal Chem („Reversible Mg-Ion Insertion in a Metastable One-Dimensional Polymorph of V2O5„). „Currently, lithium-ion technology dominates; however, the safety and long-term supply of lithium remain serious concerns. By contrast, magnesium is much more abundant than lithium, has a higher melting point, forms smooth surfaces when recharging, and has the potential to deliver more than a five-fold increase in energy density if an appropriate cathode can be identified.”
Venadium Pentaoxide
A redesigned metastable phase of vanadium pentoxide (V2O5) shows extraordinary performance as a cathode material for magnesium batteries. The graphic compares the conventional (right) and metastable structures of V2O5. (Image: Justin Andrews, Texas A&M University)
Ironically, the team’s futuristic solution hinges on a redesigned form of an old Li-ion cathode material, vanadium pentoxide, which they proved is capable of reversibly inserting magnesium ions.
„We’ve essentially reconfigured the atoms to provide a different pathway for magnesium ions to travel along, thereby obtaining a viable cathode material in which they can readily be inserted and extracted during discharging and charging of the battery,” Banerjee says.
This rare phenomenon is achieved by limiting the location of the magnesium ions to relatively uncomfortable atomic positions by design, based on the way the vanadium pentoxide is made – a property known as metastability. This metastability helps prevent the magnesium ions from getting trapped within the material and promotes complete harvesting of their charge-storing capacity with negligible degradation of the material after many charge-recharge cycles.

The Ins and Outs of Intercalation
Banerjee, a Davidson Professor of Science in the Texas A&M Department of Chemistry and an affiliated faculty member in the Department of Materials Science and Engineering, has been working for a number of years to better understand ion intercalation – the critical process by which ions like lithium and magnesium move in and out of other materials within intercalation batteries.
Using one of the world’s most powerful soft X-ray microscopes – the Scanning Transmission X-ray Microscope (STXM) and X-ray Emission beamlines – at the Canadian Light Source in tandem with one of the world’s highest resolution aberration-corrected transmission electron microscopes housed at the University of Illinois at Chicago (UIC), Banerjee and collaborators from the Lawrence Berkeley National Laboratory, the UIC and Argonne National Laboratory were able to observe the unique electronic properties of their novel vanadium pentoxide and directly prove magnesium-ion intercalation into the material. Collectively, the team applied decades of combined experience in materials science to explain the fundamental reasons why this new type of vanadium pentoxide is superior to the old version as well as to Li-ion batteries.
Laptops and cell phones are two examples of the many technologies enabled by the rapid development of the lithium-ion battery, which revolutionized energy storage capacity and rechargeability in comparison to its lead-acid and nickel-metal hydride predecessors. However, given the widespread use of lithium not only in portable electronic devices but increasingly in the much larger batteries required for electric vehicles and grid energy storage, lithium is expected to be in increasingly short supply in the long-term. Furthermore, Li-ion batteries are a risky game, as highlighted by recent widely publicized reports detailed in Scientific American, Reuters and Forbes, for example, in which Li-ion-powered devices have either caught fire or exploded as a result of the fundamental flammability and reactivity of lithium.
„Apart from being much safer for consumer applications, magnesium-ion technology is appealing fundamentally because each magnesium ion gives up two electrons per ion – twice the charge, whereas each lithium ion gives up only one,” says Texas A&M chemistry graduate student and NASA Space Technology Research Fellow Justin Andrews, first author on the team’s paper. „This means that, all other considerations aside, if you can store as much magnesium in a material as you can store lithium, you immediately almost double the capacity of the battery.”

Double the Capacity, Double the Trouble
But for all their perceived advantages, magnesium batteries have proven too good to be true since they were first proposed in the 1990s and essentially sidelined by a variety of problems; primarily, the lack of a suitable cathode, or positive electrode – otherwise known as the part of a battery where the magnesium ions enter during discharge of the battery to power an electronic device and then exit during charging.
„Indeed, the most exciting thing about magnesium ions – namely, that they store twice the charge in battery applications – also forms the basis for the biggest challenge,” says collaborating UIC chemist Jordi Cabana. „The higher charge of the magnesium ions make them ‘stick’ much more strongly with surrounding atoms.”
In other words, Banerjee says, the magnesium ions get waylaid as they are traversing through the paths within the cathode material. Their sluggish movement is what makes it so difficult to make viable magnesium batteries.
„In many structures, some of these interactions are very favorable, meaning that the magnesium is quite happy to sit and stay a while in those specific sites,” Andrews explains. „In our material, the magnesium is ‘frustrated’ as it moves through the lattice, because it encounters many less-than-optimal environments. In this sense, it is more than happy to just keep moving right along, leading to an improvement in capacity and diffusion.”
The team’s National Science Foundation-funded research features two additional current and former Texas A&M graduate students, Abhishek Parija and Peter M. Marley, respectively. David Prendergast, a Facility Director at Berkeley Lab’s Molecular Foundry, a U.S. Department of Energy National User Facility for Nanoscale Science Research, helped the Texas A&M team design and interpret their calculations, which were experimentally verified in part by Fakra using Berkeley Lab’s Advanced Light Source along with structural data collected at Argonne National Lab’s Advanced Photon Source. Atomic resolution images of the new form of vanadium pentoxide were collected in collaboration with UIC physicist Robert F. Klie and physics graduate student Arijita Mukherjee and show direct evidence of magnesium intercalated within the material. Battery measurements that show reversibility and confirm the robustness of the cathode material complete the story and were conducted in collaboration with Cabana and former Cabana group member Hyun Deog Yoo.
„On paper, magnesium batteries are highly desirable because they promise greater energy density on top of the ability to solve several of the key issues researchers – and unfortunately consumers – are discovering with lithium-ion batteries, including cost, safety, and performance at the most fundamental levels,” Andrews says. „But the shift from lithium- to magnesium-ion technologies is not straightforward, and the many problems encountered when designing magnesium-ion cathodes have stymied the development of these more sustainable and safer batteries.”

Working Toward a Safer Energy Future
Andrews says the team’s research marks an important turning point in the field because it represents a significant advance toward solving the cathode problem while also highlighting the inherent advantages of using much more imaginative, metastable materials like this new form of vanadium pentoxide. But even he admits there’s much more work to do before this particular ’90s trend comes back in vogue.
„While this research has provided a great deal of insight, there are still several other fundamental problems to overcome before magnesium batteries become a reality,” Andrews adds. „Nevertheless, this work moves magnesium batteries one step closer to reality – namely, a reality where batteries would be less-expensive, lighter and safer for allowing for easier adoption to large-area formats necessary for electric vehicles and to store energy generated by solar and wind sources.”
Source: Texas A&M University

Ceramica de vindecare cu auto-spargere, inspirată de oase, capabilă de recuperare rapidă(Bone-inspired self-crack-healing ceramics capable of quick full strength recovery)

Ceramica auto-vindecată a fost descoperită de un grup de cercetare YNU în 1995. Ușoare și rezistente la căldură, au atras atenția globală pentru utilizarea lor potențială ca materiale de turbină în motoarele de avioane. grupul de cercetare intenționează să dezvolte produse ceramice inovatoare, rezistente la căldură, care nu se vor rupe nici măcar atunci când sunt crăpate prin selectarea unor faze eficiente de vindecare a vindecătorului și, prin urmare, manipularea precisă a capacității de auto-vindecare a ceramici

Posted: Feb 05, 2018

Bone-inspired self-crack-healing ceramics capable of quick full strength recovery

(Nanowerk News) A NIMS-YNU research group discovered that self-healing ceramics undergo three healing stages analogous to bone healing processes: inflammation, repair and remodeling. Using clues provided by bone healing mechanisms, the group added a healing activator to crystalline grain boundaries, enabling the ceramic to fully heal cracks in as little as one minute at 1,000°C, the operating temperature of an aircraft engine (Scientific Reports, „A Novel Design Approach for Self-Crack-Healing Structural Ceramics with 3D Networks of Healing Activator”).
Self-healing process in ceramics
(Left and middle) Self-healing process in ceramics, which completes in as little as one minute. (Right) A network of manganese oxide (green) facilitates self-healing (Image: NIMS)
Self-healing ceramics were discovered by an YNU research group in 1995. Lightweight and heat-resistant, they have been drawing global attention for their potential use as turbine materials in aircraft engines.
However, their self-healing mechanisms had been poorly understood, and cracks only fully healed within a limited temperature range between 1,200 and 1,300°C. Therefore, identification of the mechanism and development of ceramics capable of rapid self-healing within a larger temperature range have long been sought.
The present research group found that self-healing processes occur in three stages: when a ceramic cracks, oxygen enters though the crack and reacts with silicon carbide—a ceramic component—to form silicon dioxide (the inflammation stage). Alumina—a base ceramic material—and silicon dioxide then react to form a gap filling material, sealing the crack (the repair stage).
Finally, the filler crystallizes to restore the original strength in the cracked part (the remodeling stage). In addition, based on the insight that the bodily fluid network in humans promotes the healing of damaged bones, the research group added a trace amount of a healing activator – manganese oxide – to alumina grain boundaries as a 3D network structure.
As a result, newly developed ceramics healed cracks in as little as approximately one minute at 1,000°C, compared to conventional ceramics, which heal cracks in 1,000 hours at 1,000°C.
Based on these results, the research group plans to develop innovative, heat-resistant ceramics which will never break even when cracked by selecting effective healing activator phases and thereby precisely manipulating the self-healing capability of ceramics.
This project was carried out by a research team led by Senior Researcher Toshio Osada (Research Center for Structural Materials (RCSM), NIMS), Group Leader Toru Hara (RCSM, NIMS), Principal Researcher Taichi Abe (RCSM, NIMS), Takahito Ohmura (Deputy Director of the RCSM, NIMS), Chief Researcher Masanori Mitome (International Center for Materials Nanoarchitectonics, NIMS) and Professor Wataru Nakao (Faculty of Engineering, YNU).
Source: National Institute for Materials Science

Echipa de cercetare a materialelor luminează calea pentru LED-uri mai eficiente(Materials research team lights the way for more efficient LEDs)

a studiat perovskitul de halogenuri de plumb cu trei compoziții diferite, inclusiv clorul, bromul și iodul. Nanocristalele fabricate din aceste compuși și aliajele lor pot fi reglate pentru a emite lumină la lungimi de undă care acoperă întreaga gamă vizibilă, păstrând în același timp emisia rapidă de lumină care le conferă performanțe superioare.

Posted: Jan 31, 2018

Materials research team lights the way for more efficient LEDs

(Nanowerk News) Researchers at the U.S. Naval Research Laboratory (NRL) Center for Computational Materials Science, working with an international team of physicists, have revealed that nanocrystals made of cesium lead halide perovskites (CsPbX3), is the first discovered material which the ground exciton state is „bright,” making it an attractive candidate for more efficient solid-state lasers and light emitting diodes (LEDs) (Nature, „Bright triplet excitons in caesium lead halide perovskites”).
„The discovery of such material, and understanding of the nature of the existence of the ground bright exciton, open the way for the discovery of other semiconductor structures with bright ground excitons,” said Dr. Alexander Efros, research physicist, NRL. „An optically active bright exciton in this material emits light much faster than in conventional light emitting materials and enables larger power, lower energy use, and faster switching for communication and sensors.”
The work, which was partially sponsored by the Office of Naval Research through a program managed by Dr. Chagaan Baatar, studied lead halide perovskites with three different compositions, including chlorine, bromine, and iodine. Nanocrystals made of these compounds and their alloys can be tuned to emit light at wavelengths that span the entire visible range, while retaining the fast light emission that gives them their superior performance.
Dr. Alex Efros, Dr. Noam Bernstein, Dr. John Michopoulos, Dr. John Lyons; Naval Research Laboratory
Pictured standing (l-r) are NRL researchers Dr. Alex Efros and Dr. Noam Bernstein; sitting (l-r) are Dr. John Michopoulos and Dr. John Lyons. (Image: U.S. Naval Research Laboratory)
Semiconductors emit light when bound pairs of electrons and holes, known as excitons, recombine in a process called radiative decay.
„In all known semiconductors and semiconductor nanostructures, the lowest energy state for a bound electron-hole pair is a ‘dark’ state,” said Efros. „This means the material emits light slowly and weakly.”
Because in perovskite nanocrystals the lowest energy exciton is bright, the time it takes for the electron and hole to recombine and emit light, known as their radiative lifetime, is 20 times faster than conventional materials at room temperature and 1000 times faster at cryogenic temperatures.
It is known, that quantum-dot based LEDs, or QLEDs, can suffer from „droop,” or reduced efficiency, at high pumping intensity due to processes that dissipate the energy of excitons before they have time to emit light. The decreased radiative lifetime should make it possible for LEDs based on these perovskites to use all of the energy input to create light before it is dissipated through slower processes.
„The increased rate of light emission of these materials holds great promise for various technological applications that rely on LEDs and lasers,” Efros said. „In principle, the 20 times shorter lifetime could therefore lead to 20 times more intense LEDs and lasers.” The power of a laser depends on the gain of the material it is made of, and this gain is proportional to the radiative emission rate.
Communication in free space using visible light, which makes it possible to transmit information in tight beams for long distances without fiber optic or copper cables, would also benefit from the increased light emission rates. „The maximum bandwidth of the communication system is limited by the rate at which the LEDs can turn on and off, and the shorter radiative lifetime translates directly into faster switching and therefore a higher data transmission rate,” says Efros.
Source: By Daniel Parry, Naval Research Laboratory