O bază mai bună pentru memoria 3D

Kentaro Ueda de la Centrul RIKEN pentru Știința Emergent Matter și colegii săi au investigat pyrochlore de iodură de neodim (Nd 2 Ir 2 O 7 ), un izolator magnetic cu pământuri rare, cu proprietăți neobișnuite. Spinurile din acest material sunt aranjate tetraedral și alternativ îndreptate „all-in” spre centrul tetraedrului, sau în fața „all-out”. Doua tipuri de domenii magnetice se formeaza in Nd 2 Ir 2 O 7 – ” totul in tot” sau „totul out-all-in” (fig.1) – si unele studii la scara larga au sugerat o conductivitate anormala Care se petrec la barierele dintre ele.

Posted: Feb 05, 2016
A better foundation for 3D memory (Nanowerk News) Efforts to shrink memory devices beyond the limits imposed by conventional lithography have focused on nanoscale regions, known as magnetic domain walls, which can be manipulated in three dimensions. Now, RIKEN researchers and international collaborators have detected a new type of domain wall with highly conductive, mobile metallic states that promises to make three-dimensional memory systems easier to control and miniaturize (Science, „Mobile metallic domain walls in an all-in-all-out magnetic insulator”).

Scanning probe experiments reveal that metal-like domain walls emerge at the nanoscale when two insulating, ‘all-in–all-out’ magnetic phases come into contact. (Image: Eric Yue Ma, Stanford University)
Magnetic materials contain distinct regions, known as domains, in which electrons with the same spin configuration—normally spin-up or spin-down states—are separated by domain wall boundaries. Recent theoretical studies have suggested that domain walls adopt different electronic states and become electrically active in certain magnetic insulators. But detecting metallic behavior in insulating crystals, where grains are often smaller than the width of a human hair, is experimentally challenging.
Kentaro Ueda from the RIKEN Center for Emergent Matter Science and colleagues investigated neodymium iridate pyrochlore (Nd2Ir2O7), a rare-earth-based magnetic insulator with unusual properties. Spins in this material are arranged tetrahedrally and alternately point ‘all-in’ toward the center of the tetrahedron, or face ‘all-out’. Two types of magnetic domains form in Nd2Ir2O7—‘all-in–all-out’ or ‘all-out–all-in’ (Fig. 1)—and some large-scale studies have hinted at abnormal conductivity occurring at the barriers between them.
The team used a technique called microwave impedance microscopy to obtain direct nanoscale information on the domain walls of Nd2Ir2O7. Samples were cooled to close to absolute zero and their surfaces were then scanned by an ultrasharp and highly conductive probe that senses variations in electrical resistance. The resulting images revealed the presence of narrow, curvilinear features, roughly 100 nanometers wide, that were hundreds of times more conductive than surrounding regions.
“The emergence of metallic domain walls, in spite of the fully insulating bulk state, provoked a lot of discussion in our team,” says Ueda. “Where does this behavior originate? And why is this material so special?”
The strong response of the nanoscale regions to thermal and magnetic fields provided some clues to these questions. “In conventional metals, resistivity usually depends on temperature,” explains Ueda. “The domain walls show virtually temperature-independent ohmic behavior, indicating an anomalous metallic defect or edge state.”
One potential application of this technology is magnetic random access memory (MRAM), in which data is stored by altering the electrical resistance of the recording medium. Currently, resistance changes of several tens of per cent are used in MRAM. In contrast, metallic domains can change the resistance by factors of several hundred, which should enable much more compact MRAM devices to be fabricated.

Source: RIKEN

Detectarea în timp real și fără etichete a virusurilor singulare în soluții complexe (Real-time and label-free detection of single viruses in complex solutions)

Cu senzorul nostru putem vedea mii de virusi sau nanoparticule individuale in timp real in timp ce se afla in mediul natural, cum ar fi serul sau plasma”, spune Scherr. Acest lucru ne permite sa luam masuratori dinamice si sa investigam vizual un numar mare de virusi in solutie intr-un mod care nu a fost anterior posibil.
In plus, adaugand, ca sistem de detectie, abordarea noastra elimina practic orice preparare a probelor. Deoarece agentii patogeni virale sunt vizualizati direct, fara etichete, detectati si discriminati de la un alt zgomot care poate interfera in solutia tinta, Necesar.”

Posted: Feb 05, 2016

Real-time and label-free detection of single viruses in complex solutions

(Nanowerk Spotlight) Every outbreak of a deadly or dangerous virus somewhere in the world – like last year the Ebola virus in West Africa, or just now the Zika virus in Latin America – highlights the importance of rapid detection and accurate diagnosis in health care and preventative medicine. Early detection of these diseases is a critical tool in helping control the virus and save lives.The problem is that many virus detection platforms, including conventional fluorescent label-based ones, have limitations because they are time-intensive and not easily compatible with point-of-care use without the existence of significant infrastructure and expert staff. Case in point is electron microscopy, frequently used for the direct imaging of viruses and nanoparticles, but not suitable for field operations.”Various novel optical sensor systems have been developed in an attempt to meet the needs of point-of-care environments,” M. Selim Ünlü, Distinguished Professor of Engineering in the Optical Characterization and Nanophotonics Laboratory (OCN Lab) at Boston University, tells Nanowerk. „Each of these optical sensors has unique benefits, but none has truly filled the gap to provide robust, direct, and chemically specific high-throughput single-particle visualization in a complex sample. There remains a need for a bridging technology between traditional wide-field microscopy and high-resolution electron microscopy.”In new work, Ünlü’s group and their collaborators have mated an interferometric reflectance imaging sensor developed in their lab with a microfluidic cartridge that allows them to dynamically image the sensor and visualize very small nanoparticles in solution.The researchers reported their findings in the January 13, 2016 online edition of ACS Nano („Real-Time Capture and Visualization of Individual Viruses in Complex Media”).This is the first technique capable of specifically visualizing label-free single viruses in complex solutions in real-time. label-free virus imaging (A) Picture of the first generation polymeric cartridge used for virus and nanoparticle imaging. (B) Cross section model which demonstrates the fluidic path (in blue), the sensor (in gray) and the chip and window (in yellow) not to scale. (Reprinted with permission by American Chemical Society)”We developed a simple to use tool that extends the range of light microscopy to smaller size particles allowing visualization of viruses and nanoparticles that used to require specialized liquid electron microscopy techniques,” notes Steven M. Scherr, a Graduate Research Assistant in the OCN Lab and first author of the paper.The OCN team and its collaborators have spent the past several years advancing a rapid, label-free, chip-scale photonic device that can provide affordable, simple, and accurate on-site detection. They first demonstrated the concept back in 2010 (Nano Letters, „High-Throughput Detection and Sizing of Individual Low-Index Nanoparticles and Viruses for Pathogen Identification”). In 2014, a team led by Ünlü and MED associate professor of microbiology John H. Connor followed this up with a study where they showed the capture and imaging of Ebola and Marburg surrogates using this technology (ACS Nano, „Digital sensing and sizing of vesicular stomatitis virus pseudotypes in complex media: a model for Ebola and Marburg detection”).Now, with this new work, they have refined their instrumentation to allow the simultaneous detection of multiple viruses in blood serum samples—including viruses genetically modified to mimic the behavior of Ebola and the Marburg virus.”With our sensor we can see thousands of individual viruses or nanoparticles in real-time while they are still in a natural environment, such as serum or plasma,” says Scherr. „This lets us take dynamic measurements and visually investigate a large number of viruses in solution in a way that was previously not possible.””Furthermore” he adds, „as a detection system, our approach eliminates virtually all sample preparation. Since the viral pathogens are directly (without labels) visualized, detected, and discriminated from other potentially interfering noise in the target solution, no wash step is needed.”The team has named their prototype diagnostic device the Single-Particle Interferometric Imaging Sensor (SP-IRIS). It allows for the study of unmodified viruses using visible light microscopy. It works by shining light from multi-color LED sources on viruses that are bound to the sensor surface by a coating of virus-specific antibodies. Interference of light reflected from the surface is modified by the presence of the viruses, producing a distinct signal that reveals the size and shape of each virus.The scientists point out that this technique can help bridge the gap between light microscopy and electron microscopy and be applied to both research and diagnostic applications. This tool will let researchers explore populations of synthetic and bio-nanoparticles (viruses, cellular vesicles, etc.) in solution. The sensor can also be used as a rapid and sensitive diagnostic tool.In a multiplexed detection configuration, Ebola, Marburg and Lassa antibodies on the SP-IRIS surface capture corresponding viruses specifically. As shown in the images produced by the device, SP-IRIS then identifies and counts each virus particle and classifies it based on its size. (Image: NexGen Arrays) (click on image to enlarge)”We are continuing to develop this as a rapid viral hemorrhagic fever test,” says Scherr. „This technique lets us test for Ebola as well as several other similar diseases in a single test that is both fast and sensitive and requires less sample preparation than other highly sensitive techniques.”The team’s collaborators at The University of Texas Medical Branch at Galveston (Geisbert Lab) will begin testing this cartridge with bona fide Ebola samples in the near future. The experiments will be done using the in-liquid imaging approach described in the manuscript using an automated reader created by Nexgen Arrays, a spinout company that commercializes the SP-IRIS platform.”We would like to see a highly multiplexed virus detection panel that can differentiate between a number of viruses that present with similar symptoms available in an easy-to-use disposable cartridge platform,” adds Ünlü. „Also, our technique allows for characterization of viruses. An exciting new application area for our technology is the quality control application for the emerging oncolytic viruses.”

Video: This movie demonstrates virus binding and single virus detection. It represents the actual binding sped up by a factor of 100. The initial images at the beginning of the experiment show very few particles present on the sensor surface. Accumulation of virus begins rapidly and is sustained for the 60 minute experiment. The movie was created using the images acquired from the SP-IRIS sensor system with minimal postprocessing (AVI). (Video: Optical Characterization and Nanophotonics Laboratory at Boston University)The team wants to continue to push the limit on the smallest particles they can see with this technique and improve the cartridge to make the test easy enough for anyone to use. Although imaging ultra-small particles in solution is difficult, optical detection remains an invaluable tool.By Michael Berger – Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology:

Nanomaterialul unei noi clase

Cercetătorii de cercetare au dezvoltat o nouă tehnică care produce un material care este în același timp puternic, dur și rigid. Pentru a realiza acest lucru, oamenii de știință au folosit mai întâi o procedură standard, folosită pe scară largă atunci când lucrează cu nanoparticule, prin care nanoparticulele din ceramică de fier sunt depozitate într-o gamă regulată. Acest lucru se face cu ajutorul acidului oleic organic, care intră în golul îngust între nanoparticule și le ține împreună

Posted: Feb 05, 2016
Nanomaterial of a new class (Nanowerk News) Classical materials such as ceramics, metals and polymers have their typical mechanical properties. They are hard, soft, strong, flexible or stiff. Hamburg research scientists have now synthesized a material that unites several different properties, and could thereby open the way to new applications in medical engineering and manufacturing. The scientists from the Hamburg University of Technology (TUHH), the University of Hamburg, the Helmholtz Centre Geesthacht and DESY have presented their novel nanocomposite in the journal Nature Materials („Organically linked iron oxide nanoparticle supercrystals with exceptional isotropic mechanical properties”).

Ultra-high vacuum chamber at the DESY-NanoLab, in which the spectroscopic analysis was carried out to characterise the nature of the bond formed by the oleic acid molecules. (Image: DESY)
This new class of material could for example be suitable for filling dental cavities, or manufacturing watch cases. The materials used in applications like these need to be both hard and damage-tolerant.
The research scientists have developed a new technique which produces a material that is at the same time strong, hard and stiff. To achieve this, the scientists first employed a standard procedure, widely used when working with nanoparticles, whereby ceramic iron oxide nanoparticles are deposited in a regular array. This is done with the help of organic oleic acid, which seeps into the narrow gaps between the nanoparticles and holds them together.
“The self-organisation of these nanoparticles leads to an extended, closely packed supercrystal reminiscent of atomic crystal lattices,” explains one of the authors, Axel Dreyer from the TUHH.
The crucial discovery is that by subsequently exposing the material to moderate heat levels, the resulting nanocomposite displays a much stronger cohesion and its mechanical properties are unlike those of any other.

High resolution transmission electron microscope image of the iron oxide nanoparticles, immersed in oleic acid. (Image: TUHH)
On the smallest scale, the structure of the new material resembles that of biological hard tissues, such as mother of pearl and dental enamel. It consists of uniformly sized iron oxide nanoparticles, which are coated with oleic acid. In previous studies, the bonds between the oleic acid molecules were very weak and due to so-called Van der Waals’ forces. By drying and pressing the material at an elevated temperature and then applying a controlled thermal treatment, the scientist have now managed to create a much stronger bond between the oleic acid molecules, thereby markedly improving the mechanical properties of the nanocomposite.
Since oleic acid is very often used when processing other nanoparticles too, this new method could potentially improve the mechanical properties of a great many other nanocomposites as well. The bonding properties of the oleic acid, which serves as an adhesive, have been examined spectroscopically by the staff of the DESY-Nanolab. “Our measurements showed that the oleic acid molecules survive the thermal treatment and form additional crosslinks during the process,” reports co-author Andreas Stierle, a Leading Scientist at DESY. “This important finding can serve as the basis for successfully modelling the mechanical properties of this novel material.”

Source: Deutsches Elektronen-Synchrotron

Descoperirea proprietăților specifice ale materialelor carbonice pe bază de grafit

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

Seamănă mai bine eficiențele în celulele solare monocristaline de siliciu

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

Blocuri constructive bidimensionale pentru nanomaterialele în vrac bazate pe blocuri de construcție 2D

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

A roadmap for bulk nanomaterials based on 2D building blocks

(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 toward new bulk nanostructured materials 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.

Este lignina petrolul brut al viitorului?

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

Un nou răsucire pe tehnologia veche ar putea aduce culoarea vie la putere redusă (New twist on old tech could bring living color at low power

Polimerii electrochromici constituie o clasă specială de materiale care pot trece de la culori la culori și înapoi, când se modifică sarcina electrică. Adoptarea largă a acestora a fost totuși împiedicată deoarece această transformare depinde de cât de repede electronii pot intra și ieși din material, ceea ce poate dura câteva secunde, în funcție de grosimea filmului. De ce nu faceti filmele mai subtiri, astfel incat sa schimbe culoarea mai repede? Idee bună, dar, din păcate, reducerea grosimii peliculei răstoarnă culorile contrastului lor, oferindu-vă o nuanță semitransparentă negru atunci când ceea ce ați dorit a fost un negru impenetrabil, opac.
Un afișaj bazat pe această schemă ar avea o serie de nanograme care acționează ca pixeli cu o singură culoare, ale căror culori, adăugând sau scăzând, ar produce toate culorile curcubeului, pixelii individuali având niveluri reglabile de luminozitate sau contrast.

Posted: Feb 04, 2016
New twist on old tech could bring living color at low power (Nanowerk News) By marrying state-of-the-art nanometer-scale gratings with a Space Age-era thin-film polymer, researchers working at the National Institute of Standards and Technology (NIST) have developed a new technology for building power-sipping full-color video displays, switches and routers for optical signals, as well as smart windows and coatings (Nature Communications, „High-contrast and fast electrochromic switching enabled by plasmonics”).

In this schematic, light enters from above and encounters a nanometer-scale grating made of aluminum and coated with a special ‘electrochromic’ material. Light passes through the nanograting as surface plasmons, oscillations that travel at the interface of a metal and a dielectric (insulating) material. The spacing of the slits serves to filter out all but one color of light, and an additional layer of silicon nitride further spectrally purifies the escaping light. (Image: T. Xu and A. Agrawal/NIST) (click on image to enlarge)
Electrochromic polymers make up a special class of materials that can switch from clear to colored and back again when their electrical charge changes. Their wide adoption, however, has been hindered because this transformation depends on how quickly electrons can get into and out of the material, which can take several seconds depending on the thickness of the film. Why not just make the films thinner so they’ll change color faster? Good idea, but unfortunately, reducing the film’s thickness robs the colors of their contrast, giving you a semitransparent black tint when what you wanted was an impenetrable, opaque black.
If the choice between being slow or weakly colored weren’t bad enough, an electrochromic display using an additive color scheme—in which red, green and blue are mixed to achieve full color—would need up to six transparent electrically conducting layers to work, adding substantially to the cost of manufacturing.
Using some clever engineering, the researchers overcame this impasse by layering a thin film of electrochromic polymer over an aluminum nanograting. In their setup, the light first encounters the nanograting which, depending on the spacing of the slits, filters out all but one color of light. The electrochromic coating serves to modulate that light by allowing all or some (or none) of it to pass. A display based on this scheme would have an array of nanogratings acting as single-color pixels whose colors would, by adding or subtracting them, produce all the colors of the rainbow, with the individual pixels having adjustable levels of brightness or contrast.
But how does combining a thin film of electrochromic polymer with a nanograting make up for the just-described deficiencies of using said thin film? According to co-lead author Amit Agrawal, it’s all about the architecture.
“Because the electrochromic film that coats the sidewalls of the nanograting is so thin, it’s very easy for electrons to make their way through and change its opacity,” Agrawal says. “The slits are much narrower (about 60 nanometers) than the wavelengths of light they are transmitting (from about 400 to 700 nanometers). This forces the incoming light to cling to the interface between the metal and the electrochromic layer on its way down the slits. And because the grating is so much deeper (about 250 nanometers) than it is wide, and the walls of the slits are coated with electrochromic polymer all the way down, it can reduce the light’s intensity to the same degree as if the light were passing through a much thicker layer of electrochromic film, enabling a great amount of control.”
NIST Fellow Henri Lezec, an author of the paper, says the setup they have now uses a liquid electrolyte, a chemical that facilitates the proper flow of electrons, which is not ideal for manufacturability and reliability, but that it could easily be replaced with a more physically stable and compact solid-state electrolyte.
Alec Talin, a co-author based at Sandia National Laboratories, says that the next step in extending this principle would be toward reflective, sunlight-readable displays that do not require an energy-consuming backlight.

Source: The National Institute of Standards and Technology

Oțeluri cu oxid de metal: O nouă opțiune de manipulare a proprietăților interfețelor

Am reușit să combinăm doi oxizi de metal de tranziție foarte diferiți: în timp ce în electronii titanați, legăturile chimice sunt puternic localizate în jurul ionilor, în partea de nickelat acești electroni sunt împărțiți între ionii de nichel și oxigen și, prin urmare, foarte covalent „, Explică Manuel Bibes.
Când se pun împreună ambele materiale, o anumită încărcare se transferă de la stratul de titanat la cel de aluminiu. Ei au investigat acest proces de transfer de sarcină pentru eșantioane care conțin diferite elemente de pământuri rare în stratul de nichelat, cum ar fi Lanthanum, Neodymium și Samarium la BESSY II.

Posted: Feb 04, 2016
Metal oxide sandwiches: New option to manipulate properties of interfaces (Nanowerk News) Sandwich systems of thin film transition metal oxides display surprising properties at their interfaces. In case of the paradigmatic example of Lanthan-Aluminate ( LaAlO3) and Strontium-Titanate (SrTiO3) both materials are insulators and non-magnetic, while their interface has been observed to display ferromagnetism, high electrical conductivity and even superconductivity.
Now the team of Manuel Bibes, CNRS Thales at Palaiseau, France, in collaboration with scientists at HZB around Sergio Valencia and several European groups, devised a new approach to tailor interface properties. Together they designed a series of experiments at the synchrotron source BESSY II to shed more light on the emergence of such property changes, identifying a new „knob” for their control (Nature Physics, „Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces”).

This is a sketch of the structure of both metal oxide layers. Interesting new properties can arise at the interface. (Image: M. Bibes)
Rare-Earth Elements influence charge transfer
The samples, which the team of Manuel Bibes did produce, consisted of a sandwich of 2 nm Gadolinium-Titanate (GdTiO3) and „R”-Nickelate (RNiO3) films, where R is a rare-earth element. „We have been able to combine two very different transition metal oxides: whereas in the titanate electrons in the chemical bonds are strongly localized around the ions, in the nickelate side these electrons are shared between Nickel- and Oxygen-ions, and thus highly covalent”, Manuel Bibes explains.
When putting both materials together some charge is transferred from the titanate layer to the nickelate one. They investigated this charge transfer process for samples containing different rare-earth elements in the nickelate layer such as Lanthanum, Neodymium and Samarium at BESSY II.
Their results show that the charge transfer at the interface between the materials strongly depends on the rare earth element in the nickelate layer. Different rare-earth elements have different atomic radii (size).This modifies the interaction between the Ni and O atoms and the degree of „covalency” between Ni and O changes. This was already known, but now the scientists have observed that this also affects the charge transferred from the GdTiO3 to the Nickelate film. „This is the key result”, Sergio Valencia from HZB explains. „We have found a new „knob”. Covalency (which is controlled by changing R) controls the charge transfer between the titanate and the nickelate.”
Ferromagnetism observed, superconductivity still searched
Tuning the charge transfer in this way might allow to control the formation of new interfacial phases too. For example, the scientists observed a new ferromagnetic phase at the interface. „Our work may help in the ongoing quest for cuprate-like superconductivity in nickelate heterostructures”, Valencia says. „We hope that this study will help to design better interfaces for exploring new exciting new phases of matter at interfaces between covalent materials”, Bibes adds.

Source: Helmholtz-Zentrum Berlin für Materialien und Energie

Cercetătorii caută mijloace eficiente de împărțire a apei cu nanoroduri

Hidrogenul din aceste reacții ar putea alimenta vehicule cu pile de combustie cu hidrogen curate sau ar putea fi combinat cu dioxid de carbon pentru a produce metanol, care ar putea fi distribuit prin sistemul nostru existent de combustibil lichid. Această din urmă abordare are avantajul suplimentar de a scoate dioxidul de carbon din atmosferă.

Posted: Feb 04, 2016
Researchers seek efficient means of splitting water with nanorods (Nanowerk News) Photovoltaics promise to help meet our energy needs by turning sunlight into electricity. We can’t run everything that way, but with a little tweaking, photovoltaic materials can use solar energy to split water into hydrogen and oxygen.
Cornell researchers are studying how this works, hoping to make the process more efficient and less expensive. “There are several existing systems, but none actually work well,” said Peng Chen, the Peter J. W. Debye Professor of Chemistry.
Hydrogen from these reactions could power vehicles with clean-burning hydrogen fuel cells, or could be combined with carbon dioxide to make methanol, which could be distributed through our existing liquid-fuel system. The latter approach has the added benefit of taking carbon dioxide out of the atmosphere.
Chen and colleagues studied water-splitting activity on the surface of nanorods of the semiconductor titanium dioxide, finding that variations in the structure of the surface determine where and how the reaction takes place. They report their results in the Feb. 4 issue of the journal Nature („Sub-particle reaction and photocurrent mapping to optimize catalyst-modified photoanodes”).

Flashes of fluorescence seen under a microscope show where chemical reactions to (b) split water molecules or (c) electric currents take place on a nanorod of photovoltaic material. The outline of the rod laid over flash images is taken from the scanning electron microscope image at right.
When a photon of light hits a crystal of titanium dioxide, the added energy kicks an electron into a higher energy level, leaving behind a “hole” – a space where an electron ought to be but isn’t, that looks like a positive charge. If electrodes are attached to the crystal, the free electrons will flow through a circuit as an electric current.
But in the presence of a catalyst – in this case cobalt borate – the array of positive charges can withdraw electrons from a water molecule (whose formula can be written as H-O-H), pulling it apart into a positively charged proton – the nucleus of a hydrogen atom – and a neutral hydroxyl radical, or OH. The OH radicals combine into hydrogen peroxide (H-O-O-H), which the catalytic reaction again pulls apart into protons and oxygen.
To study the reaction, Chen’s research team focused a powerful microscope on titanium dioxide rods about 127×1,735 nanometers in a microfluidic chamber through which water was flowed. A light microscope can’t see chemical reactions, so Chen employed a technique he calls “fluorescence microscopy,” adding chemicals to the water that change into a fluorescent material when the reactions take place. One changes in the presence of free electrons; the other changes in the presence of OH radicals, which are produced when water is split. When the sample is zapped with a laser to induce fluorescence, the microscope sees flashes of light that reveal where the reactions are taking place.
Alternating from one probe to the other, they observed that the reactions were not distributed evenly across the surface. Water splitting occurred only at certain “hotspots” that seem to be characterized by some irregularities in the surface or the presence of a few “doping” atoms.
“This gives us a way to improve the process,” Chen said. “Now we know where to deposit the catalyst according to the map of the hole and electron reactions on each nanorod.”
The researchers propose a method for selectively depositing catalyst on the areas that will be most productive.

Source:By Bill Steele, Cornell University

Oamenii de știință îndrume nanoparticulele de aur pentru a forma supralaturi „diamante”

poate deschide o cale către noi materiale care să profite de proprietățile optice și mecanice ale acestei Structura cristalină pentru aplicații precum tranzistoare optice, materiale de schimbare a culorii și materiale ușoare, dar dure.

Posted: Feb 04, 2016
Scientists guide gold nanoparticles to form ‘diamond’ superlattices (Nanowerk News) Using bundled strands of DNA to build Tinkertoy-like tetrahedral cages, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have devised a way to trap and arrange nanoparticles in a way that mimics the crystalline structure of diamond. The achievement of this complex yet elegant arrangement, as described in a paper published February 5, 2016, in Science („Diamond family of nanoparticle superlattices”), may open a path to new materials that take advantage of the optical and mechanical properties of this crystalline structure for applications such as optical transistors, color-changing materials, and lightweight yet tough materials.
„We solved a 25-year challenge in building diamond lattices in a rational way via self-assembly,” said Oleg Gang, a physicist who led this research at the Center for Functional Nanomaterials (CFN, www.bnl.gov/cfn/) at Brookhaven Lab in collaboration with scientists from Stony Brook University, Wesleyan University, and Nagoya University in Japan.

Schematic illustration of the experimental strategy: Double stranded DNA bundles (gray) form tetrahedral cages. Single stranded DNA strands on the edges (green) and vertices (red) match up with complementary strands on gold nanoparticles. This results in a single gold particle being trapped inside each tetrahedral cage, and the cages binding together by tethered gold nanoparticles at each vertex. The result is a crystalline nanoparticle lattice that mimics the long-range order of crystalline diamond. The images below the schematic are (left to right): a reconstructed cryo-EM density map of the tetrahedron, a caged particle shown in a negative-staining TEM image, and a diamond superlattice shown at high magnification with cryo-STEM. (click on image to enlarge)
The scientists employed a technique developed by Gang that uses fabricated DNA as a building material to organize nanoparticles into 3D spatial arrangements [ www.bnl.gov/newsroom/news.php?a=11728]. They used ropelike bundles of double-helix DNA to create rigid, three-dimensional frames, and added dangling bits of single-stranded DNA to bind particles coated with complementary DNA strands.
„We’re using precisely shaped DNA constructs made as a scaffold and single-stranded DNA tethers as a programmable glue that matches up particles according to the pairing mechanism of the genetic code-A binds with T, G binds with C,” said Wenyan Liu of the CFN, the lead author on the paper. „These molecular constructs are building blocks for creating crystalline lattices made of nanoparticles.”
The difficulty of diamond
As Liu explained, „Building diamond superlattices from nano- and micro-scale particles by means of self-assembly has proven remarkably difficult. It challenges our ability to manipulate matter on small scales.”
The reasons for this difficulty include structural features such as a low packing fraction-meaning that in a diamond lattice, in contrast to many other crystalline structures, particles occupy only a small part of the lattice volume-and strong sensitivity to the way bonds between particles are oriented. „Everything must fit together in just such a way without any shift or rotation of the particles’ positions,” Gang said. „Since the diamond structure is very open, many things can go wrong, leading to disorder.”
„Even to build such structures one-by-one would be challenging,” Liu added, „and we needed to do so by self-assembly because there is no way to manipulate billions of nanoparticles one-by-one.”
Gang’s previous success using DNA to construct a wide range of nanoparticle arrays suggested that a DNA-based approach might work in this instance.
DNA guides assembly
The team first used the ropelike DNA bundles to build tetrahedral „cages”-a 3D object with four triangular faces. They added single-stranded DNA tethers pointing toward the interior of the cages using T,G,C,A sequences that matched up with complementary tethers attached to gold nanoparticles. When mixed in solution, the complementary tethers paired up to „trap” one gold nanoparticle inside each tetrahedron cage.
The arrangement of gold nanoparticles outside the cages was guided by a different set of DNA tethers attached at the vertices of the tetrahedrons. Each set of vertices bound with complementary DNA tethers attached to a second set of gold nanoparticles.
When mixed and annealed, the tetrahedral arrays formed superlattices with long-range order where the positions of the gold nanoparticles mimics the arrangement of carbon atoms in a lattice of diamond, but at a scale about 100 times larger.

Brookhaven Lab’s Oleg Gang describes the idea of using DNA to drive the self-assembly of materials from nanoscale particles.
„Although this assembly scenario might seem hopelessly unconstrained, we demonstrate experimentally that our approach leads to the desired diamond lattice, drastically streamlining the assembly of such a complex structure,” Gang said.
The proof is in the images. The scientists used cryogenic transmission electron microscopy (cryo-TEM) to verify the formation of tetrahedral frames by reconstructing their 3D shape from multiple images. Then they used in-situ small-angle x-ray scattering (SAXS) at the National Synchrotron Light Source (NSLS, www.bnl.gov/ps/), and cryo scanning transmission electron microscopy (cryo-STEM) at the CFN, to image the arrays of nanoparticles in the fully constructed lattice.
„Our approach relies on the self-organization of the triangularly shaped blunt vertices of the tetrahedra (so called ‘footprints’) on isotropic spherical particles. Those triangular footprints bind to spherical particles coated with complementary DNA, which allows the particles to coordinate their arrangement in space relative to one another. However, the footprints can arrange themselves in a variety of patterns on a sphere. It turns that one particular placement is more favorable, and it corresponds to the unique 3D placement of particles that locks the diamond lattice,” Gang said.
The team supported their interpretation of the experimental results using theoretical modeling that provided insight about the main factors driving the successful formation of diamond lattices.
Sparkling implications
„This work brings to the nanoscale the crystallographic complexity seen in atomic systems,” said Gang, who noted that the method can readily be expanded to organize particles of different material compositions. The group has demonstrated previously that DNA-assembly methods can be applied to optical, magnetic, and catalytic nanoparticles as well, and will likely yield the long-sought novel optical and mechanical materials scientists have envisioned.
„We’ve demonstrated a new paradigm for creating complex 3D-ordered structures via self-assembly. If you can build this challenging lattice, the thinking is you can build potentially a variety of desired lattices,” he said.

Source: Brookhaven National Laboratory

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