au sintetizat materialul perfect pentru protecția organelor respiratorii, cercetare analitică și alte scopuri practice;Vorbind despre posibilele aplicații ale acestui material, oamenii de știință susțin că este mai mult decât purificarea evidentă a aerului și a apei din particule
Cercetarea utilizează compozite cu legături de înaltă calitate și altele în mod deliberat făcute cu legături mai slabe. Diferențele în rezultatele de a ajuta echipa îmbunătăți detectarea defectelor sau deteriorare. Un ecran de computer prezinta pete luminoase sau întunecate indică posibilele probleme care, și a realiza un grafic legăturile suprapuși adâncimea probleme potențiale la timpul indicat pe imagine.
| Posted: Feb 01, 2016 | |
Nondestructive testing: Looking inside composites(Nanowerk News) Researcher David Moore holds a rectangle of hard carbon composite material, smooth with a faint woven pattern on its surface. The sample shows normal wear and tear until he turns it over to reveal a circular impact mark with cracks radiating from it. |
|
| The question for Moore, his Sandia National Laboratories colleague Timothy Briggs in California and their teams is whether the impact caused significant, hidden damage inside the composite. They’re developing nondestructive ways to detect damage in composites, using traditional medical inspection techniques such as X-rays and sonograms and advanced methods including infrared imaging, ultrasonic spectroscopy and computed tomography. | |
 |
|
| Sandia National Laboratories technologist Andrew Lentfer passes a roller probe over a composite as researcher David Moore checks data on a screen. The nondestructive testing technique sends sound waves into the composite material, returning data with each swipe of the roller probe. | |
| Sandia began studying composites several years ago to see whether the lightweight materials could be used in national security applications. While a composite in a cell phone needs to last only a couple of years, “typically materials for national security applications must survive for decades. This makes you think differently about where and why you would use a material,” said Moore, who works in the Structural Dynamics and X-ray/Nondestructive Evaluation department. “We need to study the lifecycle of a component. We tend to think deeply about the consequences of fracture or deformation and how we can verify what happened.” | |
| The work supports many aspects of Sandia’s national security mission, including energy efficiency and performance improvements in lightweight vehicles or wind turbine blades, said Briggs of Sandia California’s Lightweight Structures organization. | |
| Composites join together separate materials with different characteristics. They often consist of a soft polymer matrix with reinforcing fibers like carbon, Kevlar or glass. Composites can use bundles of thinner-than-a-hair carbon strands that yield a high strength-to-weight ratio. The final shape and strength is obtained after heating the part in an industrial oven that sets the polymer resin and yields the qualities necessary for a structural component. | |
| Composites are increasingly important in aerospace and other industries because they’re strong and weigh less than metals. Most can be bonded to metal for such uses as aircraft wings, making planes lighter and less expensive to fly. | |
| Outside surface of a composite doesn’t hint at what’s inside | |
| “We have a rich history of understanding metals and their failure mechanisms,” Moore said. “Composite materials are very different.” | |
| If a service truck backs into a composite aircraft fuselage, an examination of the impact site might not detect damage under the surface. That highlights the reason for nondestructive techniques that can fully evaluate how composites react in various circumstances. | |
| The research team is assessing the accuracy of nondestructive methods and how they could be used on a production floor. “You have to know what could go wrong in the processing steps and how to circumvent those, and then you want to make sure if you’re going to make one or a hundred or a thousand that you’re making them the same way all the time,” Moore said. | |
| “Once we establish the limits of detectability, the threshold of good, bad and questionable, we’ll be able to say, ‘We want this composite bonded to this material with a defined quality and it shall be inspected with this technique,’” he said. | |
| Sandia’s Lightweight Structures Lab defines and consolidates materials to study, using particular stack sequences of composite material layers to tailor strength and stiffness. It works in concert with the National Security Campus in Kansas City, Missouri, in everything from developing process methods to building prototypes to qualifying designs for particular applications. | |
| After making composites, the fabrication lab cuts out specimens for instrumented experiments — abusing the carefully made sample to study deformation, fracture and damage growth. Briggs “pulls, stretches, torques and crushes them. He performs these mechanical experiments so we can understand the fracture mechanisms around failure,” Moore said. “Then we try to detect some of those failure modes.” | |
| Characterizing material properties helps computer modeling, simulation | |
| “The fundamental characterization of composites measures material properties and structural characteristics, which in turn provides information to validate computer modeling and simulation,” Briggs said. | |
| Data from these destructive tests is correlated with nondestructive evaluations from Moore’s team to understand what caused the material to respond the way it did, Briggs said. The effort hinges on close collaboration with Sandia’s materials characterization groups and modeling and simulation colleagues to help validate their computer-based simulations. | |
| Composites must support a particular weight and size. “Anyone can build a structure to carry the load, but we have to design our structures to fit within a geometric envelope and be lightweight,” Briggs said. “We cannot simply over-engineer to unrealistic levels. We have to be very smart and efficient with our designs, yet provide enough margin for long-term reliability.” | |
| Materials bonded in an oven or autoclave often have different thermal expansion rates — aluminum expands more than fiber-reinforced plastics, for example. Once a composite cools after curing, residual stresses can build up inside, particularly at interfaces. If the composite can’t handle those stresses, the bonds can fail. | |
| Sandia is developing advanced techniques to complete sample inspections in less than 5 minutes in some cases. “This is a way to gain a lot of information very quickly about the quality of the bonds,” Moore said. | |
| Team studies specific nondestructive techniques | |
| His team uses the deliberately mistreated composites to assess such inspection techniques as advanced ultrasonics, flashed or active thermography and computed tomography. | |
| Ultrasonic testing has been around for 60 years, but computers and other improvements now allow study of more complex applications. Technologist Andrew Lentfer demonstrates, scanning a piece of composite with a handheld ultrasonic roller that resembles a small paint roller with a hollow, water-filled barrel. As he scans the composite’s layers, a computer screen maps them in color: Yellow-green is OK; blue indicates weakness. Rollers can scan curved surfaces, even large ones like airplanes. | |
| Fibers and interfaces in a composite scatter ultrasonic waves moving through the material. Moore compares it to ocean waves: “If a wave hits a rock face in the ocean it moves around it; if a wave washes up on the sand it gets absorbed; and if it hits a seawall the wave energy is redirected quickly. Those are the same fundamentals we investigate: ultrasonic energy moving through a composite matrix.” | |
| Knowledge gained from characterizing materials helps develop new nondestructive techniques “so when we establish an inspection criteria, we have a better feel for what we can detect and what we cannot,” he said. | |
| Flashed thermography, commercially available for more than 20 years, flashes very high-energy light onto a surface for 15 microseconds, then an infrared camera watches how the surface cools. The process takes only minutes. | |
| “It’s very fast, but you have to understand the fundamentals of heat flow and how the material surface either gives off heat to its surroundings or transfers heat within itself,” Moore said. | |
| Studies use good, not-so-good composites to test differences | |
| The research uses composites with high-quality bonds and others deliberately made with weaker bonds. Differences in results help the team improve detection of defects or damage. A computer screen shows light or dark spots indicating possible problems, and an overlaid graph ties the depth of the potential problem to the time indicated on the image. | |
| “The question becomes, is that a concern? Is that a crack or not?” Moore said. “We’ll be able to answer those questions. If the defect propagates deep into the material, we may not detect it. It’s wise to understand the capabilities of the technique and then perform the math and science behind it.” | |
| Computed tomography systems are efficient for finding small defects. The technique rotates a sample 360 degrees while taking 1,000 images, similar to a medical CT scan, and generates an image from each thin slice of the object. Since each image taken is two dimensional, computer algorithms reconstruct, calculate, locate and display everything to represent the object in three dimensions. | |
| “Once the 3-D image is reconstructed, you look at the front surface and then start moving through the thickness to view what is below the surface,” Moore said. “This technology gives us a knowledge baseline and validates how the other techniques are performing.” | |
| Sandia must ensure designs meet requirements by specifying and qualifying an inspection technique, and now is writing inspection procedures for the National Security Campus, Moore said. “Once we establish criteria and limits of acceptability, the product definition can be established,” he said. |
| Source: Sandia National Laboratories |
Read more: Nondestructive testing: Looking inside composites
Autorii au folosit date din spectroscopie infraroșie și termogravimetrie pentru a identifica rezistența interacțiunii dintre sondă și suprafața de oxid, care le-a ajutat, de asemenea, să determine tipul de legare la suprafață.
Ei au stabilit doi parametri cheie: în primul rând, densitatea speciilor de suprafață adsorbite utilizate pentru a caracteriza interacțiunea moleculei de sondă cu suprafața. Acest parametru depinde de natura nanoparticulelor de oxid și de existența nanoporilor. Al doilea parametru exprimă raportul dintre moleculele conținute în stratul de suprafață având un comportament dinamic din sticlă față de numărul total al moleculelor adsorbite.
Studiul arată că valoarea densității de suprafață poate fi utilizată pentru a diviza compozitele în mai multe grupuri. Acest lucru ajută la determinarea faptului că moleculele de sondă aplicate pe suprafața unui grup dat pot prezenta interacțiuni similare, așa cum se observă în suprafețele aceleiași familii.
| Posted: Feb 29, 2016 | |
Scrutinizing the tip of molecular probes(Nanowerk News) Studies of molecules confined to nano- or micropores are of considerable interest to physicists. That’s because they can manipulate or stabilise molecules in unstable states or obtain new materials with special properties. |
|
| In a new study published in EPJ Plus („Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species”), Stefan Frunza from the National Institute of Materials Physics in Romania and colleagues have discovered the properties of the surface layer in probe molecules on the surface of oxide particles. These properties depend on the interaction at the interface. | |
| In this particular study, probes are formed by adsorption of rod-like cyanophenyl derivates on the surface of oxide particles. The authors found that their surface layers behave like glass-forming liquids. | |
 |
|
| The solid lines indicate the temperature range used to estimate the amount of molecules loaded onto the probe. | |
| What physicists already knew is that confinement of molecules may induce disorder. Confinement and disorder have a considerable influence both on the structure of the trapped molecule but also on its mobility. As a result, they also affect aspects such as molecular dynamics upon relaxation of the material. Such structurally well-defined monolayers on solid surfaces will allow researchers to model a large variety of interfacial phenomena. | |
| The authors used data from infrared spectroscopy and thermogravimetry to identify the strength of the interaction between the probe and the oxide surface, which also helped them determine the type of bonding to the surface. | |
| They established two key parameters: firstly, the density of the adsorbed surface species used to characterise the interaction of the probe molecule with the surface. This parameter depends on the nature of the oxide nanoparticles and on the existence of nanopores. The second parameter expresses the ratio of the molecules contained in the surface layer having a glassy dynamic behaviour to the total number of the adsorbed molecules. | |
| The study shows that the value of the surface density can be used to divide the composites into several groups. This helps to determine that the probe molecules applied to the surface of a given group can display similar interactions, as observed in surfaces of the same family. |
| Source: SciencePOD |
Read more: Scrutinizing the tip of molecular probes
au dezvoltat un material care menține stabilitatea A unui catalizator „dispersat^ și de constând dintr-un singur atom și de modalitatea de a produce boabe mici de platină prin exploatarea proprietăților substratului
Platina este unul dintre metalele costisitoare utilizate ca catalizatori în noile tehnologii folosite pentru procesele chimice industriale, sursele de energie regenerabilă, controlul poluării și multe alte scopuri. În special, se utilizează pentru celulele de combustie, dispozitive care transformă energia chimică direct în energie electrică, fără ardere. Cercetările au arătat că cea mai mare eficiență este obținută atunci când catalizatorul este disponibil sub formă de nanoparticule (mai mici de 10-9 m). Pur și simplu, cu cât este mai mare dispersia materialului și cu cât dimensiunea particulelor este mai mică, cu atât mai mult este disponibilă pentru cataliză. Din nefericire, legile termodinamicii determină particulele să se „lipsească” unul de celălalt și să formeze clustere mai mari, motiv pentru care materialul devine mai puțin eficient în timp. Deci, ce se poate face pentru a menține dispersia maximă a „nanopulberii”
| Posted: Feb 29, 2016 | |
Nanoparticles on nanosteps(Nanowerk News) New technologies are starved for efficient and inexpensive catalysts. The best materials are made up of nanoparticles, whose properties are the result of their small size. The single catalyst particles have, however, an ugly tendency to cluster into larger particles, thereby reducing their effectiveness. A group of scientists from the International School of Advanced Studies in Trieste and the DEMOCRITOS centre of the Istituto Officina dei Materiali of the Italian National Research Council (IOM-CNR), with the collaboration of other institutions, have developed a material that maintains the stability of a “dispersed” catalyst, thus maximising the efficiency of the process and decreasing costs and wastage. |
|
| The study has just been published in Nature Communications („Creating single-atom Pt-ceria catalysts by surface step decoration”). | |
 |
|
| Nanoparticles adhering to steps. | |
| Platinum is one of the costly metals used as catalysts in new technologies employed for industrial chemical processes, renewable energy sources, pollution control and many other purposes. In particular, it is used for fuel cells, devices that turn chemical energy directly into electrical energy, without combustion. Research has shown that the greatest efficiency is achieved when the catalyst is available in the form of nanoparticles (smaller than 10-9 m). Simply put, the greater the dispersion of the material and the smaller the size of the particles, the more is it available for catalysis. Unfortunately, the laws of thermodynamics cause the particles to “stick” to one another and form larger clusters, which is why the material becomes less effective over time. So what can be done to maintain maximal dispersion of the “nanopowder”? | |
| A group of SISSA/CNR IOM scientists (with the collaboration of the Univerzita Karlova in Prague) has studied a way to produce tiny platinum grains consisting of one atom only and to keep them dispersed in a stable manner, by exploiting the properties of the substrate on which they rest. | |
| “Theoretical work demonstrated that irregularities in the surface known as steps and observed in experiments conducted at the Trieste Synchrotron tend to attract and separate the nanoparticles, causing them to remain literally attached in the form of single atoms”, explains Stefano Fabris, CNR-IOM/SISSA research fellow. | |
| “The particles adhering to the steps were no longer visible even using an atomic resolution microscope” explains Nguyen-Dung Tran, a SISSA PhD student. “However, their presence was detected by spectroscopy, so they were indeed there, but they were no longer visible or free to move around”. “Our computer simulations solved this dilemma, showing that the particles on the steps are reduced to single atoms” adds Matteo Farnesi Camellone (CNR-IOM), another author of the study. | |
| “If the surface is engineered to contain a large number of these defects, then the force that binds the particles to the substrate effectively offsets the aggregation force”, explains Fabris. The theoretical work, led by Fabris, allowed the researchers to develop a “system model” on the computer able predict the behaviour of the material. The model’s predictions were confirmed by the experimental measurements. Materials like this can be used for fuel cell electrodes, with far lower costs than the current ones. | |
| “Reducing the amount of platinum used in fuel cell electrodes is a priority, not only to contain costs but also to ensure environmental sustainability, as also indicated by the recent European directives” concludes Fabris. The European project ChipCAT, which funded this research, aims precisely to achieve this goal. |
| Source: SISSA | |
Read more: Nanoparticles on nanosteps
Au demonstrat că prin combinarea celor trei elemente este posibil să se obțină un material de 2 atomi gros, cu adevărat 2D, cu proprietăți care pot fi reglate pentru a se potrivi diferitelor aplicații dincolo de ceea ce este posibil cu grafenul
| Posted: Feb 29, 2016 | |
New 2-D material could upstage graphene(Nanowerk News) A new one atom-thick flat material that could upstage the wonder material graphene and advance digital technology has been discovered by a physicist at the University of Kentucky working in collaboration with scientists from Daimler in Germany and the Institute for Electronic Structure and Laser (IESL) in Greece. |
|
| Reported in Physical Review B, Rapid Communication („Prediction of a new graphenelike Si2BN solid”), the new material is made up of silicon, boron and nitrogen – all light, inexpensive and earth abundant elements – and is extremely stable, a property many other graphene alternatives lack. | |
 |
|
| The atoms in the new structure are arranged in a hexagonal pattern as in graphene, but that is where the similarity ends. The three elements forming the new material all have different sizes; the bonds connecting the atoms are also different. As a result, the sides of the hexagons formed by these atoms are unequal, unlike in graphene. (Image: Madhu Menon) | |
| „We used simulations to see if the bonds would break or disintegrate – it didn’t happen,” said Madhu Menon, a physicist in the UK Center for Computational Sciences. „We heated the material up to 1,000 degree Celsius and it still didn’t break.” | |
| Using state-of-the-art theoretical computations, Menon and his collaborators Ernst Richter from Daimler and a former UK Department of Physics and Astronomy post-doctoral research associate, and Antonis Andriotis from IESL, have demonstrated that by combining the three elements, it is possible to obtain a one atom-thick, truly 2D material with properties that can be fine-tuned to suit various applications beyond what is possible with graphene. | |
| While graphene is touted as being the world’s strongest material with many unique properties, it has one downside: it isn’t a semiconductor and therefore disappoints in the digital technology industry. Subsequent search for new 2D semiconducting materials led researchers to a new class of three-layer materials called transition-metal dichalcogenides (TMDCs). TMDCs are mostly semiconductors and can be made into digital processors with greater efficiency than anything possible with silicon. However, these are much bulkier than graphene and made of materials that are not necessarily earth abundant and inexpensive. | |
| Searching for a better option that is light, earth abundant, inexpensive and a semiconductor, the team led by Menon studied different combinations of elements from the first and second row of the Periodic Table. | |
| Although there are many ways to combine silicon, boron and nitrogen to form planar structures, only one specific arrangement of these elements resulted in a stable structure. The atoms in the new structure are arranged in a hexagonal pattern as in graphene, but that is where the similarity ends. | |
| The three elements forming the new material all have different sizes; the bonds connecting the atoms are also different. As a result, the sides of the hexagons formed by these atoms are unequal, unlike in graphene. The new material is metallic, but can be made semiconducting easily by attaching other elements on top of the silicon atoms. | |
| The presence of silicon also offers the exciting possibility of seamless integration with the current silicon-based technology, allowing the industry to slowly move away from silicon instead of eliminating it completely, all at once. | |
| „We know that silicon-based technology is reaching its limit because we are putting more and more components together and making electronic processors more and more compact,” Menon said. „But we know that this cannot go on indefinitely; we need smarter materials.” | |
| Furthermore, in addition to creating an electronic band gap, attachment of other elements can also be used to selectively change the band gap values – a key advantage over graphene for solar energy conversion and electronics applications. | |
| Other graphene-like materials have been proposed but lack the strengths of the material discovered by Menon and his team. Silicene, for example, does not have a flat surface and eventually forms a 3D surface. Other materials are highly unstable, some only for a few hours at most. | |
| The bulk of the theoretical calculations required were performed on the computers at the UK Center for Computational Sciences with collaborators Richter and Andriotis directly accessing them through fast networks. Now the team is working in close collaboration with a team led by Mahendra Sunkara of the Conn Center for Renewable Energy Research at University of Louisville to create the material in the lab. The Conn Center team has had close collaborations with Menon on a number of new materials systems where they were able to test his theory with experiments for a number of several new solar materials. | |
| „We are very anxious for this to be made in the lab,” Menon said. „The ultimate test of any theory is experimental verification, so the sooner the better!” | |
| Some of the properties, such as the ability to form various types of nanotubes, are discussed in the paper but Menon expects more to emerge with further study. | |
| „This discovery opens a new chapter in material science by offering new opportunities for researchers to explore functional flexibility and new properties for new applications,” he said. „We can expect some surprises.” |
| Source: University of Kentucky |
Read more: New 2-D material could upstage graphene
Au demonstrat recent transferul energetic de înaltă eficiență între tijele cuantice semiconductoare și enzimele luciferazăș transfer de energie prin rezonanță bioluminescență
| Posted: Feb 29, 2016 | |
Chemists combine biology, nanotechnology to create alternate energy source(Nanowerk News) Chemists in Syracuse University’s College of Arts and Sciences have made a transformational advance in an alternate lighting source–one that doesn’t require a battery or a plug. |
|
| Associate Professor Mathew Maye and a team of researchers from Syracuse, along with collaborators from Connecticut College, have recently demonstrated high-efficient energy transfer between semiconductor quantum rods and luciferase enzymes. Quantum rods and luciferase enzymes are nanomaterials and biomaterials, respectively. When combined correctly, these materials produce bioluminescence–except, instead of coming from a biomaterial, such as a firefly enzyme, the light eminates from a nanomaterial, and is green, orange, red, or near-infrared in color. | |
 |
|
| A schematic of the nano-biosystem (top) and an electron microscope image of quantum rods. | |
| The findings are the subject of a recent article in ACS Nano („Probing Bioluminescence Resonance Energy Transfer in Quantum Rod–Luciferase Nanoconjugates”). | |
| „Think of our system as a design project,” Maye says. „Our goal has been to build a nano-biosystem that’s versatile enough to teach us a lot, while allowing us to overcome significant challenges in the field and have practical applications. The design involves materials from our chemistry and biology labs, as well as various nanoscience and self-assembly tools. It’s a true team effort with multiple collaborations.” | |
| Maye illustrates his point by referencing quantum rods, each of which is four nanometers wide and 50 nanometers long. (A nanometer is 1 billionth of a meter.) „The rods were chemically synthesized with amazing precision,” he says. „To get the best information, we realized that we needed at least two different types of rods, each with three synthetically tuned variations, and up to 10 different assembly conditions.” | |
| Having a wide range of variables has enabled Maye and his team to learn more about the science of nano-biology energy transfer. | |
| Prior to becoming a postdoc at the University of Notre Dame, Rabeka Alam G’13 led the project at Syracuse as a Ph.D. student. She says this work illuminates a special kind of interaction known as bioluminescence resonance energy transfer (BRET). „In nanoscience, a quantum dot or rod is typically an energy donor,” she says. „In our case, the energy came from bioluminescent luciferase.” | |
| With BRET, the enzyme is attached to the surface of the rod. Luciferin is added, and acts as a kind of fuel. When the enzyme and fuel interact, they release an energy that is transferred to the rod, causing it to glow. | |
| „The trick to increasing the efficiency [of BRET] is finding the right donor-acceptor combination, which requires different rods and enzymes,” says Liliana Karam, a Syracuse Ph.D. student who currently heads up the project. „Thanks to our colleagues at Connecticut College, we have genetically manipulated enzymes of multiple colors that are attached to the rods, which, in turn, are prepared in our lab at Syracuse.” | |
| Maye says the quantum rods are composed of semi-conductive elements–specifically, an outer shell of cadmium sulfide and an inner core of cadmium selenide. By manipulating the size and shape of the core, the length of the rod, and the way the enzymes are attached and packed onto the surface of the rod, researchers are able to alter the color and intensity of the light that is emitted, thus demonstrating the overall efficiency of the process. | |
| Postodc Tennyson Doane, a senior member of the Maye Research Group, says one of the breakthroughs of the project involves a special type of rod known as a „rod-in-rod.” The group has been hypothesizing why this particular rod results in high-efficiency gains. | |
| „When you have a rod-shaped core, the resulting fluorescence is polarized, meaning circular light comes in, and linearly polarized light comes out,” says Doane, adding that the shape of the material makes BRET more efficient. „We believe that, when aligned correctly with the luciferase-excited state, the rod experiences efficiency gains that otherwise are not witnessed in a self-assembled nanosystem. Controlling the enzyme location and bioluminescence polarization may, one day, lead to novel ‘light switches,” in which only certain enzymes around the quantum rod are able to interact via BRET.” | |
| Maye calls this „using biology for non-biological applications.” | |
| „Our nanorods are made of the same materials used in computer chips, solar panels, and LED [light-emitting diode] lights. At the moment, our system works best in the red to near-infrared range, which has longer wavelengths than visible light, and is invisible to the eye,” he says, alluding to night-vision goggles, medical imaging, and rapid microbial detection. „Our work is patent-pending at Syracuse. Perhaps, we’ll someday have firefly-covered nanorods that can be inserted into LED lights and don’t require a plug.” |
| Source: Syracuse University |
Read more: Chemists combine biology, nanotechnology to create alternate energy source
echipă de cercetare a susținut-o în trecut și dezvăluie recent proprietățile unice ale materialelor carbonice pe bază de grafit cum ar fi grafenul , Care ar putea fi folosite ca materiale noi în dispozitive electronice sau pentru cataliză.
| Posted: Feb 04, 2016 | |
Discovery of the specific properties of graphite-based carbon materials(Nanowerk News) University of Tsukuba Faculty of Pure and Applied Sciences Associate Professor Takahiro Kondo and Professor Junji Nakamura, in cooperation with Researcher Donghui Guo and Professor Susumu Okada of the same faculty, have shown from detailed measurements that in atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields, Landau levels manifest corresponding to super strong magnetic fields of approximately 100 tesla across bilayer graphene (Scientific Reports, „Observation of Landau levels on nitrogen-doped flat graphite surfaces without external magnetic fields”). |
|
 |
|
| Prof. Junji Nakamura (front), Dr. Donghui Guo (left), Assoc. Prof. Takehiro Kondo (right). | |
| There has been some debate thus far that the source of Landau levels generated under non-magnetic fields has been pseudo-magnetic fields induced by asymmetries, but in this study the researchers observed Landau levels on atomically flat surfaces without asymmetries, showing for the first time the existence of Landau levels generated by sources other than asymmetries. | |
| These results further endorse the “domain model” (the mechanism for Landau level generation under a non-magnetic field) that this same research team has advocated for in the past, and newly reveals the unique properties of graphite-based carbon materials such as graphene, which could be used as new materials in electronic devices or for catalysis. | |
| Graphite-based carbon materials such as graphene exhibit powerful electrical conductivity and excellent strength in small quantities, so there is hope that they may contribute to next-generation materials in a variety of fields. The discovery of new physical properties of carbon materials in this study could lead to new applications in environmental materials like electronic materials that make use of electronic state controls such as band gap controls, catalysts, or batteries. |
| Source: University of Tsukuba |
Read more: Discovery of the specific properties of graphite-based carbon materials
a dezvoltat așa-numita „metoda de turnare cu semințe unice” folosind un cristal de semințe pentru metoda de turnare cu siliciu. Cercetătorii au reușit să producă lingouri de înaltă calitate, cu impurități scăzute de siliciu monocristal (mono-siliciu).
Noua metodă constă în dizolvarea siliciului în interiorul unui creuzet și în creșterea siliciului unic cristalin dintr-o sămânță mică. În mod special, costurile de producție pot fi reduse prin această metodă, comparativ cu metodele convenționale.
| Posted: Feb 04, 2016 | |
Seeding better efficiencies in monocrystalline silicon solar cells(Nanowerk News) Researchers at MANA have developed the ‘single-seed cast method’ that is a new method of silicon casting („Advantage in solar cell efficiency of high-quality seed cast mono Si ingot”). Compared with conventional casting, the new method enabled dramatic improvements in the crystalline quality of the silicon that are expected to improve the efficiency of silicon solar cells. |
|
 |
|
| Photograph of the silicon ingot grown with the optimum conditions observed in the current study. | |
| The conversion efficiency of silicon solar cells –that are the mainstream of commercial photovoltaics– is now going to reach 20% using single crystalline silicon. Increasing conversion efficiency is recent target for adding higher value to the solar cells. However, it is not possible to achieve such high efficiencies using conventional cast multicrystalline silicon. Furthermore, since semiconductor grade single crystal silicon is too expensive for solar cells, there is strong demand for the development of a ‘third type’ of silicon as an alternative to multicrystalline and single-crystalline semiconductor silicon. | |
| As a solution to this problem, a research team led by Takashi Sekiguchi, Group Leader of the Nano Device Characterization Group, Nano-Electronic Materials Unit, International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), and Koichi Kakimoto, Professor of Kyushu University, has developed the so-called ‘single-seed cast method’ using a seed crystal for the silicon cast method. The researchers succeeded in producing high quality, low impurity ingots of single crystal silicon (mono-silicon). | |
| The new method consists of dissolving silicon inside a crucible and growing single crystalline silicon from a small seed. Notably, production costs can be reduced by this method it compared with conventional methods. | |
| Importantly, solar cells produced using crystals produced by the new method yielded solar cells with conversion efficiencies of 18.7%, which approach the value of 18.9% obtained for cells produced with dislocation free semiconductor-silicon (CZ silicon) wafers. | |
| In the future, further reductions of crystalline defects and impurities are expected to yield conversion efficiencies greater than CZ silicon. |
| Source: International Center for Materials Nanoarchitectonics |
Read more: Seeding better efficiencies in monocrystalline silicon solar cells
Autorii au concluzionat că materialele 2D sunt probabil grupul cel mai promițător de blocuri de construcții nanometrice bine construite pentru construirea materialelor inginerice nanostructurate în vrac: „Foi 2D sunt capabili să formeze un contact intim față-în-față și pot să se îndoaie, În timpul asamblării, unele se pot deforma chiar plastic la nivelul unui singur strat, prin urmare, ele pot construi mostre de volum de înaltă densitate cu volume și porozități libere reglabile, în termeni de stabilitate, dacă materialele stratificate părinte sunt stabile termodinamic, Foi 2D exfoliate pentru a fi rezistente la sinterizare și capabile să mențină grosimea lor cu un singur strat sau cu câteva straturi. Cu toate acestea, suprafața lor ridicată conduce, de asemenea, la o reactivitate chimică mai ridicată decât la materialele în vrac, care ar trebui abordate pentru aplicațiile țintă.Încapsularea adecvată sau pasivarea suprafeței ar putea contribui la atenuarea acestei probleme fără a sacrifica performanța
Posted: Feb 04, 2016
(Nanowerk Spotlight) Two-dimensional (2D) materials like graphene and molybdenum disulfide (MoS2) are known to have unique properties. The family of 2D structures with a wide range of chemistries can open the door for better understanding of differences between properties of 2D and 3D materials; lead to identification of useful properties of 2-D carbides, nitrides, oxycarbides and other related structures; and ultimately result in new applications.A recent study („Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes)”) has shown that the family of 2D materials, in particular MXenes (read more about MXenes in our previous Nanowerk Spotlight), can be greatly expanded based on a new ‘double metal’ strategy.With these 2D systems complementing other nanostructures, a diverse array of well-defined nanostructured materials has now become available to allow researchers to focus more on scaling up the syntheses of these nanoscale building blocks, and studying them in bulk forms rather than as individual units.This scaling up of nanomaterials in the broader context of materials science and engineering is the topic of a Perspective article in ACS Nano („Bulk Nanostructured Materials Based on Two-Dimensional Building Blocks: A Roadmap”), where the authors construct a roadmap for assembling nanoscale building blocks into bulk nanostructured materials, and define some of the critical challenges and goals.As the authors write, 2D sheets are uniquely well-suited in this roadmap for constructing dense, bulk-sized samples with scalable material performance or interesting emergent properties. But no matter what structures are used, „when nanostructures with better-than-bulk material performances are used in bulk form, it is critical that those extraordinary nanoscale properties can be scaled to the macroscopic level.”A good example is the challenge to scale up the properties of carbon nanotubes (CNTs) to the macroscale. Materials engineers are keen to exploit the outstanding mechanical properties of CNTs for applications in fibers, composites, fabrics and other larger-scale structures and devices all the way to futuristic applications like a space elevator. The ability to fabricate continuous, multifunctional yarns represents an important step in this direction (read more: „Spinning kilometers-long, multi-layered carbon nanotube yarns„).
Bulk form of nanomaterials: Top-down and bottom-up. (a) Bulk nanostructured materials were initially demonstrated with metals processed by extensive plastic deformation, which significantly reduces their grain sizes, leading to unusual mechanical properties. The curve illustrates the general trend of an increasing volume fraction of grain boundaries with decreased grain sizes. On the other hand, discrete nanoscale entities are often assembled into bulk forms for creating new properties or to be used in applications. Some examples include the following: (b) plasmonic colloidal crystals with vibrant colors, tunable by the assembly of (c) octahedral Ag nanocrystals (© American Chemical Society). (d) Twisted yarns of carbon nanotubes with extraordinary strength and toughness (© American Association for the Advancement of Science). (e) Lamellar membrane made of exfoliated clay sheets showing unipolar ionic transport and high ionic conductivity (© Nature Publishing Group). (f) Pelletized powders of crumpled graphene balls with scalable surface area. (g) Dense yet nanoporous graphene monoliths19 with moldable shapes and extraordinary performance as supercapacitors (© Nature Publishing Group). (click on image to enlarge)With regard to defining a roadmap for the bottom-up assembly toward new bulk nanostructured materials, the authors point out that there are a number of challenges, which can be summarized as scalability and stability.”Scalability refers to both scalable synthesis of high-quality processable nanoscale building blocks, and scalable material performance, where the properties of the nanoscale units are still accessible in the final bulk pieces. Stability of the building blocks is also important, because they should not sinter into large grains or chemically transform into less useful materials during processing or application.”
A roadmap showing bottom-up assembly route toward new bulk nanostructured materials, highlighting the challenges of scalability and stability. (Reprinted with permission by American Chemical Society)The authors conclude that 2D materials are probably the most promising group of well-defined nanoscale building blocks for constructing bulk nanostructured engineering materials: „2D sheets are capable of forming intimate face-to-face contact, and they can bend, wrinkle, or crumple during assembly. Some can even plastically deform at the single layer level. Therefore, they can construct high-density bulk samples with tunable free volumes and porosities. In terms of stability, if the parent layered materials are thermodynamically stable, then we might expect the exfoliated 2D sheets to be sintering-resistant and capable of maintaining their single- or few-layer thickness. However, their high surface area also leads to higher chemical reactivity than in bulk materials, which should be addressed for target applications. Proper encapsulation or surface passivation could help to mitigate this problem without sacrificing performance.”By Michael Berger – Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny.
Read more: A roadmap for bulk nanomaterials based on 2D building blocks
Un pas spre transformarea industrială a ligninei în intermediari chimici valoroși se face prin dezvoltarea a doi noi fotocatalizatori. Componenta lor principală este dioxidul de titan TiO2, depozitat pe un purtător selectat în mod corespunzător: într-un caz, acestea sunt nanocompozite care conțin Fe2O3 și în al doilea – zeoliți (aluminosilicați), cu un mic adaos de fier. Fotocatalizatorul cu nanocompozite de oxid de fier a venit în strânsă colaborare cu cercetătorii din Spania, condus de Prof. Rafael Luque (Applied Catalysis B Environmental, „Sinteza ușoară cu ultrasunete a TiO2 susținută pe nanocompozite magnetice pentru foto-oxidarea selectivă a alcoolului benzilic
| Posted: Feb 04, 2016 | |
Is lignin the crude oil of the future?(Nanowerk News) We associate refineries with crude oil and a dense tangle of technical fittings. They may, however, change in the future – if crude oil is replaced by lignin, a product currently treated as industrial waste. The research route leading towards this goal is being paved by new photocatalysts, developed by the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw. They allow lignin-based model compounds to be transformed into useful chemical substances, in addition, the reactions take place under conditions that occur in nature. |
|
| It’s not a pretty sight: an oily, almost black sludge. In addition, it stinks – much, much worse than it looks. Inspecting lignin, especially up close and with an unblocked nose, it’s hard to believe that it is being treated as a potentially important renewable source of valuable aromatic compounds for the chemical industry. Unfortunately, despite many years of attempts by teams of chemists from all over the world, we still have not managed to develop efficient methods of converting lignin. | |
| We are being brought a step closer to cheap solar biorefineries capable of processing lignin on an industrial scale by the new photocatalysts developed at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw, Poland, in cooperation with the Warsaw University of Technology and the University of Cordoba. | |
 |
|
| A step towards photobiorefineries: photocatalysts from the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw, Poland, transform lignin-based model compounds into useful chemical substances. Pictured above: Prof. Juan Carlos Colmenares. | |
| In nature, lignin is present primarily in wood, where it is responsible for wood’s consistency and hardness. We can observe the spectacular results of its existence on a daily basis; it is the reason why trees do not creep over the ground, but conversely – reach even dozens of metres up into the sky, in spite of gravity. The lignin content of wood is typically from 10 to 40% depending on the tree species (the species also affects the chemical composition of the lignin). | |
| In industry, lignin is produced in large quantities during the manufacture of paper, as a waste product in the wood softening process. World reserves of lignin are huge and they are continuing to increase. The current estimate is even 300 billion tons, so it is a raw material that is more ubiquitous than crude oil (whose reserves are approx. 230 billion tons). | |
| „From the chemical point of view lignin is a natural polymer with a very complex three-dimensional structure, constructed of, among others, many derivative aromatic compounds including those from various phenyl alcohols. This chemical richness makes lignin a potentially very interesting raw material for the chemical industry. Unfortunately, at the same time, this is its curse, because it is very difficult to develop chemical reactions that would efficiently transform lignin into a specific, single chemical compound, readily suitable for further processing,” says Prof. Juan Carlos Colmenares (IPC PAS). | |
| The difficulty in processing lignin means that today it is an industrial waste product of minimum significance that is burdensome for the environment: only 2% of its reserves are further processed, and the resulting chemical compounds are, in any case, of relatively small added value. | |
| A step towards the industrial transformation of lignin into valuable chemical intermediates is being taken by the development of two new photocatalysts. Their main component is titanium dioxide TiO2, deposited on a suitably selected carrier: in one case these are nanocomposites containing iron oxide Fe2O3, and in the second – zeolites (aluminosilicates), with a small addition of iron. The photocatalyst with iron oxide nanocomposites came about in close cooperation with scientists from Spain, led by Prof. Rafael Luque (Applied Catalysis B Environmental, „Mild ultrasound-assisted synthesis of TiO2 supported on magnetic nanocomposites for selective photo-oxidation of benzyl alcohol”). | |
| „In order to ensure the most uniform coverage of the particles, the process of deposition of titanium dioxide on the medium is carried out in the presence of ultrasounds, according to a method developed at our Institute,” stresses Prof. Colmenares. | |
| In laboratory studies at the Institute, lignin with the addition of either one or other of the photocatalysts was exposed to ultraviolet light, simulating the spectrum of incoming radiation from the Sun. Both catalysts proved surprisingly effective in the transformation of the benzyl alcohol present in the structure of lignin into a benzaldehyde, a substance used, among others, in the production of dyes and in the perfume industry. In the best case, after only four hours, up to half of the original benzyl alcohol content of lignin underwent conversion. | |
| In industrial applications, the selectivity of the reaction is also important: the more selective the reaction, the less polluted its products are by unnecessary and usually difficult to separate additives. It turned out that in a solution that had reacted with the participation of photocatalysts there was up to 90% of the target substance. | |
| „In the presence of our photocatalysts, illuminated by light imitating solar radiation, the reactions took place spontaneously in lignin-based model compounds, at ordinary atmospheric pressure and at a temperature of approx. 30 degrees Centigrade, thus in conditions naturally occurring in direct sunlight. This is the exact opposite of traditional refineries, which require very complicated and expensive to maintain technical infrastructure,” notes Prof. Colmenares. | |
| The new photocatalysts have one more advantage: they are cheap, because they do not require expensive precious metals, such as palladium, and their carriers are common materials. In addition, one of the photocatalysts has magnetic properties and thus after conversion has taken place, it can be easily recovered from the solution and reused. | |
| The results obtained by the scientists from Warsaw and Cordoba are promising, however, they only apply to photocatalysts with model compounds. For the photocatalysts to effectively process real lignin – heterogeneous and often with a varying chemical composition – further studies and tests are required. | |
| The work on photocatalysts involved a group of employees of the Department of Materials Science and Engineering of the Warsaw University of Technology, headed by Prof. Krzysztof Kurzyd?owski. It is there, using advanced research techniques, that a detailed determination of the physical parameters of the new photocatalysts was carried out. |
| Source: Institute of Physical Chemistry of the Polish Academy of Sciences |
Read more: Is lignin the crude oil of the future?
au dezvoltat prima teorie statistică cunoscută despre duritatea grafenului policristalin, care se face cu depunere chimică de vapori și a constatat că acesta este într-adevăr puternic
