Categorie: Materiale noi cu proprietati fizicomecanice noi

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

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

Posted: Nov 20, 2017

Spin current from heat: New material increases efficiency

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

Circuitele sintetice pot recolta energie luminoasă(Synthetic circuits can harvest light energy)

Prin organizarea de pigmenti pe un schelet ADN, o echipa de cercetatori condusa de MIT a proiectat un material de recoltare a luminii care imita foarte mult structura structurilor fotosintetice care apar in mod natural.
Cercetătorii au arătat că materialul lor sintetic poate absorbi lumina și își poate transfera eficient energia de-a lungul căilor controlate precis. Acest tip de structură ar putea fi încorporat în materiale precum sticlă sau textile, ceea ce le va permite să recolteze sau să controleze în alt mod energia care intră în lumina soareluiCercetătorii consideră că aceste structuri sintetice ar putea fi integrate în materiale de tip 2-D și 3-D, cum ar fi sticla sau textilele, oferind acestor materiale abilitatea de a absorbi lumina soarelui și de a o transforma în alte forme de energie, cum ar fi electricitatea, folosiți energia. Structurile ar putea, de asemenea, să formeze o nouă bază pentru computerele cuantice, implementate la scară nanometrică, utilizând circuite excitonice ca porți logice cuantic

Posted: Nov 13, 2017

Synthetic circuits can harvest light energy

(Nanowerk News) By organizing pigments on a DNA scaffold, an MIT-led team of researchers has designed a light-harvesting material that closely mimics the structure of naturally occurring photosynthetic structures.
The researchers showed that their synthetic material can absorb light and efficiently transfer its energy along precisely controlled pathways. This type of structure could be incorporated into materials such as glass or textiles, enabling them to harvest or otherwise control incoming energy from sunlight, says Mark Bathe, an associate professor of biological engineering at MIT.
By organizing pigments on a DNA scaffold, a light-harvesting material closely mimics the structure of naturally occurring photosynthetic structures
By organizing pigments on a DNA scaffold, an MIT-led team of researchers has designed a light-harvesting material that closely mimics the structure of naturally occurring photosynthetic structures. (Image: MIT)
“This is the first demonstration of a purely synthetic mimic of a natural light-harvesting circuit that consists of densely packed clusters of dyes that are precisely organized spatially at the nanometer scale, as found in bacterial systems,” Bathe says.
Bathe is one of the senior authors of the new study, along with Alan Aspuru-Guzik, a professor of chemistry and chemical biology at Harvard University, and Hao Yan, a professor of chemistry and biochemistry at Arizona State University. Lead authors of the paper, which appears in Nature Materials („Programmed coherent coupling in a synthetic DNA-based excitonic circuit”), are former MIT postdoc Etienne Boulais, Harvard graduate student Nicolas Sawaya, and MIT postdoc Rémi Veneziano.

Capturing light
Over billions of years, plants and photosynthetic bacteria have evolved efficient cellular structures for harvesting energy from the sun. This process requires capturing photons (packets of light energy) and converting them into excitons — a special type of quasiparticle that can carry energy. Energy from these excitons is then passed to other molecules at a complex of protein and pigments known as a reaction center, and eventually used by the plant to build sugar molecules.
While scientists have developed reliable techniques for carrying electrons (such as semiconductors) and photons (fiber optics), coming up with ways to control excitons has proven more challenging.
Four years ago, Bathe, Aspuru-Guzik, and Yan began working on synthetic structures that could mimic natural light-harvesting assemblies. These assemblies, usually found in cell organelles called chloroplasts, have an intricate structure that efficiently captures and transports solar energy at the scale of nanometers.
“What’s really amazing about photosynthetic light-harvesting is how well it meets the organism’s needs,” says Gabriela Schlau-Cohen, an MIT assistant professor of chemistry who is also an author of the paper. “When it is required, every absorbed photon can migrate through the network of proteins that surrounds the reaction center, to generate electricity.”
The researchers set out to mimic these structures by attaching light-harvesting pigments to study scaffolds made of DNA. Over the past several years, Bathe’s lab has devised new ways to program DNA to fold in particular shapes, and last year Bathe and his colleagues created a new computer-programming tool that automates the process of designing DNA scaffolds of nearly any shape.
For this study, the researchers wanted to use DNA scaffolds to spatially organize densely packed clusters of pigments similar to those found in nature. Boulais found a 1977 paper that showed that a synthetic pigment called pseudoisocyanine (PIC) aggregates onto specific sequences of naturally occurring DNA to form the type of structure the researchers were seeking, called a J-aggregate. However, because this approach used naturally occurring DNA, there was no way to control the spacing, size, or 3-D spatial organization of the clusters.
Veneziano tested the researchers’ ability to template these J-aggregates into discrete clusters with distinct 2-D organizations using synthetic DNA, and Boulais and Sawaya worked to computationally design customizable, synthetic DNA scaffolds that organize these aggregates into circuits that absorb photons and transport the resulting excitons along a predictable path. By programming specific DNA sequences, the researchers can control the precise location and density of the clusters of dye molecules, which sit on a rigid, double-stranded DNA scaffold. They computationally modeled how factors such as the number of dye molecules, their orientation, and the distances between them would affect the efficiency of the resulting circuits, analyzing many versions of the circuits for their efficiency of energy transfer.
“Photosynthetic organisms organize their light-harvesting molecules precisely using a protein scaffold. Up to now, this kind of structural control has been difficult to realize in synthetic systems. It looks like DNA origami provides a means of mimicking many of the principles of photosynthetic light-harvesting complexes,” says Gregory Scholes, a professor of chemistry at Princeton University who was not involved in the study.
Part of the ASU team, led by co-author Su Lin, performed a series of spectroscopic measurements to demonstrate that the designed DNA structures produced the desired J-aggregates, and to characterize their photophysical properties. Schlau-Cohen, who uses advanced spectroscopy techniques to analyze light-harvesting systems, both natural and synthetic, showed that these dense pigment assemblies were able to efficiently absorb light energy and transport it along specific pathways.
“We demonstrated the ability to control the traffic patterns using J-aggregated dyes, not just how far the excitons can travel. That’s important because it offers versatility in designing such circuits for functional materials,” Bathe says.
“Bottom-up design of excitonics systems has been a focused goal of our Energy Frontiers Research Center (EFRC). I am glad to see an important stepping stone toward demonstrating bottom-up control of exciton flow,” Aspuru-Guzik says. He adds that “multidisciplinary research that tightly couples synthesis, theory, and characterization was required to get to this point.”

New materials
The researchers believe that these synthetic structures could be integrated into 2-D and 3-D materials such as glass or textiles, giving those materials the ability to absorb sunlight and convert it into other forms of energy such as electricity, or to otherwise store or harness the energy. The structures might also form a new basis for quantum computers, implemented at the nanoscale, using excitonic circuits as quantum logic gates.
The researchers now plan to explore ways to make these synthetic light-harvesting systems even better, including looking for more efficient pigments, which may lie in the recently announced Max Weaver Dye Library at North Carolina State University, which houses 98,000 unique dyes.
“There are still a lot of ways that we can imagine improving this,” Schlau-Cohen says. “We have the ability to control individual molecular parameters to explore the basic science questions of how can we transport energy efficiently in a disordered material.” Schlau-Cohen is also the senior author of a companion publication that will be published in the Journal of Physical Chemistry Letters next week.
Source: By Anne Trafton, MIT

Curentul monopole oferă un mod de a controla magneții(Monopole current offers way to control magnets)

au descoperit noi proprietăți magnetice interesante ale unui tip de material cunoscut sub numele de ” cu gheață de spin quantum. „Aceste materiale prezintă proprietăți interesante, deoarece se comportă ca „magneți frustrați” – sisteme care se pot regla în diferite stări magnetice datorită geometriei lor speciale. O proprietate importantă a acestor materiale este aceea că au monopoluri particulare virtuale care sunt fie nordice sau sudice, dar nu ca niște magneți tipici, care au în mod invariabil atât un pol de nord cât și un sud limitat împreună.

Posted: Nov 13, 2017

Monopole current offers way to control magnets

(Nanowerk News) In work published in Physical Review Letters („Quantum spin ice under a [111] magnetic field: from pyrochlore to kagomé”), scientists from RIKEN in Japan have discovered interesting new magnetic properties of a type of materials known as “quantum spin ice.”
These materials demonstrate interesting properties as they behave as “frustrated magnets”—systems that can settle into various magnetic states because of their special geometry. One important property of these materials is that they have virtual monopoles—particles that are either north or south but not like typical magnets, which invariably have both a north and south pole confined together.
Using numerical simulations, the group showed how a magnetic field could be used to control the properties of north and south poles, which are fractionalized from magnetic moments of electrons, on a frustrated magnet called a quantum spin ice.
The group first proposed a model for quantum spin ice—spin ice based on quantum properties—in 2010 in order to describe the low-energy magnetic properties of magnetic rare-earth pyrochlores—a type of mineral that show interesting physical properties.
In 2012, experiments showed that this model was valid. This system includes a quantum spin liquid state where spins—the property of electrons that lead to magnetic properties—are prevented from ordering and freezing by zero-point motion, a type of motion allowed even at zero temperature under quantum mechanics, of their monopoles. Since monopole charges are subject to a conservation law, the motion of north and south poles directly affects the direction of magnetic moments in the system.
In addition, electric charges are not carried by these monopoles, and thus the monopole current is not accompanied by an electric current that would lead to a large energy loss through Joule heat. “Because of this,” says Shigeki Onoda, the leader of the group, “monopole current offers a potentially efficient way of controlling magnets without loss.”
Through this work, the researchers revealed that there are successive transitions from the quantum spin liquid state if a magnetic field is applied in a special direction along which kagome-lattice layers and triangular-lattice layers are stacked one on top of the other.
First, the magnetization of the system rises smoothly to a value two-third of the maximum value in the quantum spin liquid state, and then remains at that level in a finite range of the field strength, which is called the 2/3 magnetization plateau. In this plateau state, the zero-point motion of monopoles are spatially confined and localized, and thus this state cannot host a coherent monopole current. H
owever, as the strength of the magnetic field is increased, the magnetization of the material eventually begins to rise again and concomitantly, the monopole charges become disproportionate and show a superfluidity. This is a magnetic analogue of a supersolid in helium 4, where the atoms show both a non-uniform spatial distribution and a superfluidity, which supports frictionless and thus dissipationless current, at extremely low temperature. The monopole supersolid phase survives until the magnetization saturates to the maximum value.
According to Onoda, “Our work indicates that the conductivity associated with the monopole current can be substantially controlled by applying a magnetic field to quantum spin ice and that it is possible to host dissipationless monopole current in the monopole supersolid phase. Our findings may also open a novel route to the efficient control of magnetism for a range of potential applications such as memory devices.”
Source: RIKEN

Un nou concept pentru un ghid de undă unidirecțional(A new concept for a unidirectional waveguide)

un nou tip de material a atras atracția de creștere: așa-numitul izolator topologic. Această clasă de materiale prezintă o proprietate foarte ciudată: ele se comportă ca izolații în interior, dar conțin stări de conducere la limitele lor. Deoarece aceste stări sunt protejate „din punct de vedere topologic”, statele sunt foarte robuste împotriva imperfecțiunilor, iar curenții electrici pot circula aproape fără disipare. Acest lucru face ca aceste materiale să fie extrem de interesante pentru sarcina de comunicare cuantică și de calcul cuantic, de exemplu.

Posted: Nov 07, 2017

A new concept for a unidirectional waveguide

(Nanowerk News) In the past decade, a new type of material has attracted raising attraction: the so-called topological insulator. This class of materials exhibits a very peculiar property: they behave like insulators in the interior, but contain conducting states at their boundaries. As these states are “topologically” protected, the states are very robust against imperfections, and electric currents can flow almost without any dissipation. This makes these materials extremely interesting for the task of quantum communication and quantum computing, for example.
Now Dr. Tao Shi (at present Chinese Academy of Sciences, Beijing) and Prof. Ignacio Cirac from the Max Planck Institute of Quantum Optics in Garching, together with Prof. Jeff Kimble from the California Institute of Technology (Pasadena, USA), have developed a detailed scheme for an experimental setup to realize a 2-dimensional topological insulator with classical optical networks (PNAS, „Topological phenomena in classical optical networks”).
concept for a unidirectional waveguide
Scheme of the optical nework. (© PNAS)
“In this network, photon modes play the role of the electronic states in a solid state layer,” explains Dr. Tao Shi. “By preparing chiral photon modes at the boundary, we may be able to build a one-way electromagnetic waveguide, in which light can only propagate in one direction, while the opposite direction is prohibited.“
Solid state crystals are characterized by their band structure. In case of an insulator, the so-called valence band, in which all electronic states are occupied, is separated from the conduction band by a large forbidden zone. This, however, only holds for infinite samples.
In case of a confined crystal or layer, the electronic states at the surface or edge, respectively, differ from those in the interior, and sometimes they emerge in the middle of the forbidden zone. As the shape of the band structure is mathematically described by a certain topological number, these systems are called in short “topological insulators”.
The chirality of the edge states is locked to the spin of the electron, and is consequently protected by time-reversal symmetry: a reverse in direction would imply a flip of the spin direction. For a certain class of materials with a “nontrivial” topological number this is not allowed. Therefore, the states are protected and robust against imperfections or deformations, as long as the perturbations are small.
In a certain class of electronic 2-dimensional topological insulators also the so-called quantum spin Hall (QSH) effect can be observed. Intuitively, this effect describes the phenomenon that electrons with different spins are subjected to oppositely directed magnetic fields.
Different from previous schemes, the scientists propose a setup made of optical passive elements such as fibres, beam splitters, and wave plates, whereby system losses are reduced to a large extent. By constructing the nodes of the network with a “bad” cavity, i.e. a cavity with high damping, they are able to dramatically enhance the topological bandgap to the scale of the free spectral range. As a consequence, the edge modes survive in the larger frequency domain with much longer lifetime. Furthermore, the interplay between the topology and the Kerr non-linearity induces the generation of squeezed edge modes.
“The optical analogue of a topological insulator paves the way towards building the one-way wave guide,” Dr. Shi points out. “Apart from that – our ultimate goal is to realize the fractional quantum Hall effect (FQHE) in this photonic system. To this end, we have to induce strong photon-photon interactions by means of atoms. We would also like to see some exotic topological phases in the photonic system, which can be very different from those observed in conventional condensed matter systems.“
Source: By Olivia Meyer-Streng, Max Planck Institute of Quantum Optics

Ridurile dau căldură unei răsturnări în grafenul colmatat(Wrinkles give heat a jolt in pillared graphene)

Măsurate de-a lungul celui mai lung plan, modelele cu octogonii au fost cu aproape 20% mai bune la transportul fononelor decât cele fără. „Rezultatele noastre arată că trăsături subtile, cum ar fi această configurație a joncțiunii, au un impact semnificativ asupra transportului termic”, a spus Shahsavari, profesor asistent de inginerie civilă și de mediu și de știință a materialelor și nanoengineering. „Având în vedere nevoile actuale în managementul termic și miniaturizarea dispozitivelor în multe nano- și microelectronice, acest studiu oferă un nou grad de libertate de a juca și de a îmbunătăți transportul termic”.

Posted: Nov 03, 2017

Wrinkles give heat a jolt in pillared graphene

(Nanowerk News) Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University engineers.
Rice materials scientist Rouzbeh Shahsavari and alumnus Navid Sakhavand first built atom-level computer models of pillared graphene – sheets of graphene connected by covalently bonded carbon nanotubes – to discover their strength and electrical properties as well as their thermal conductivity.
In a new study, they found that manipulating the joints between the nanotubes and graphene has a significant impact on the material’s ability to direct heat. That could be important as electronic devices shrink and require more sophisticated heat sinks.
graphene pillars
Heat transport through pillared graphene could be made faster by manipulating the junctions between sheets of graphene and the nanotubes that connect them, according to Rice University researchers. (Image: Lei Tao/Rice University)
The research appears in the American Chemical Society journal ACS Applied Materials and Interfaces („Asymmetric Junctions Boost In-plane Thermal Transport in Pillared Graphene”).
Researchers who study or are working to make pillared graphene have primarily viewed two characteristics of the theoretical material: the length of the pillars and their distance from each other. The new study suggests that a third parameter – the nature of the junction between the graphene and nanotubes – should also be considered.
A seamless connection between flat graphene, the atom-thick form of carbon, and round nanotubes requires adjustments to their characteristic six-member carbon rings. The simplest way is to give half the rings at the junction an extra atom. Six seven-member rings alternating with six six-member rings allow the sheet to make a 90-degree turn to become the tube.
But that’s not the optimal configuration for heat transport, according to the Rice team. It found that replacing six heptagons with three octagons would facilitate the turn while slightly stressing the graphene. That would wrinkle the graphene sheets’ top and bottom while not significantly changing transport at the junctions.
The researchers intuitively expected the wrinkles to lower thermal transport and were surprised to find that thermal transport across the „in-plane” graphene became faster with wrinkles. They determined that having fewer rings in the junctions between nanotubes and graphene meant less scattering of heat-carrying phonons, which kept them onboard for the bumpy ride.
Measured along the longest plane, models with the octagons were nearly 20 percent better at transporting phonons than those without. „Our results show that subtle features such as this junction configuration have a significant impact on thermal transport,” said Shahsavari, an assistant professor of civil and environmental engineering and of materials science and nanoengineering. „Given the current needs in thermal management and device miniaturization in many nano- and microelectronics, this study provides a new degree of freedom to play and improve thermal transport.”
The researchers thought phonon transport through the nanotubes, which they already knew was slower than in graphene, might be slower still under the influence of the octagons, but the altered interface didn’t appear to have a significant effect.
„The reason lies in the geometry,” Shahsavari said. „The lower the number of non-hexagonal rings in the junction (for example three octagons versus six heptagons), the lower the number of undesirable rings and thus lower phonon scattering and improved thermal transport.” Because the junctions can adopt many different geometries depending on the radius and chirality of the nanotube, there are many more potential configurations to be modeled, he said.
Source: Rice University

Să fie lumină (albă): Materialele noi strălucesc(Let there be (white) light: New materials shine out)

Aceste materiale ar putea fi cheile pentru diodele de lumină de generație următoare și alte dispozitive care interconvertesc lumina și electricitatea, inclusiv celulele solare.
Lumina-emitatoare de 2-D perovskites sunt atractive din cauza costurilor lor reduse și tunability. Folosind diferite lungimi de distanțiere organice di-funcționale, s-au sintetizat o serie de noi hibrizi perovskiți de bromură de plumb anorganic-anorganic, de către cercetătorii de la Universitatea Northwestern.
Schimbarea lungimii ionilor încărcați pozitiv organic (cationi) induce o distorsionare a straturilor anorganice perovskite 2-D din material, ceea ce face ca straturile să aibă o structură ondulată sau ondulată. Deoarece distorsiunea cauzată de diferitele lungimi de cationi crește, lărgimea de bandă de frecvență și durata de viață a emisiilor fotoluminescente ale materialelor cresc.

Posted: Nov 03, 2017

Let there be (white) light: New materials shine out

(Nanowerk News) Changing how we light our homes and offices could save energy, but new lighting technology requires new materials with the right properties. Materials called hybrid perovskites could be vital in making change possible.
Scientists discovered that changing the length of small spacer ions located between the perovskite’s internal layers manipulates the structure, distorting the layers to look like corrugated cardboard (Journal of the American Chemical Society, „White-light emission and structural distortion in new corrugated two-dimensional lead bromide perovskites”). The shortest spacer studied led to the most distorted structure. The structure emitted white light, comparable to commercial fluorescent lights.
The color coordinate map illustrates the colors of light emitted by different hybrid perovskites
The color coordinate map illustrates the colors of light emitted by different hybrid perovskites (with varying degrees of internal structural distortion) relative to pure white (corresponding to the yellow circle). The insert is a photo of the white light emitted by the most distorted material in the study (abbreviated α-(DMEN)PbBr4, also shown as a blue circle in the color map) after stimulation by ultraviolet radiation. (Image: Mercouri Kanatzidis, Northwestern University)
A new design tool based on understanding how spacers alter the light emitted could lead to new materials. These materials could be the keys to next-generation light-emitting diodes and other devices that interconvert light and electricity, including solar cells.
White-light–emitting 2-D perovskites are attractive because of their low cost and tunability. Using different lengths of di-functional organic spacers, a series of new hybrid organic-inorganic lead bromide perovskites were synthesized by researchers at Northwestern University.
Changing the length of the organic positively charged ions (cations) induces a distortion of the 2-D perovskite inorganic layers in the material, making the layers take on a wavy or corrugated structure. As the distortion caused by the different cation lengths increases, the frequency bandwidth and the lifetime of the materials’ photoluminescent emission increases.
Having the largest internal distortion of all the materials prepared in this study, the compound α-(DMEN)PbBr4 emits white light with a color rendering index of 73, which is similar to a commercial fluorescent light source. This correlation between structure and properties demonstrates that crystal structures of hybrid organic-inorganic perovskites can be manipulated to tune bandwidth and lifetime of the photoluminescent emission by varying the extent of the inorganic layer distortion.
With abundant choices of organic molecules available, many new exciting perovskite materials can be prepared, leading to an even deeper understanding of the science of these materials and impacting optoelectronic applications such as solid-state lighting.
Source: U.S. Department of Energy, Office of Science

Nanosilica dendritică fibroasă: nanomaterialul all-in-one pentru energie, mediu și sănătate(Dendritic fibrous nanosilica: all-in-one nanomaterial for energy, environment and health)

DFNS pare a fi Nanomaterial All-in-One și are un potențial imens pentru dezvoltarea viitoare. Deși DFNS a fost dotat cu proprietăți fizice și chimice excelente și prezintă rezultate excepționale în diferite aplicații, evoluția DFNS din studiile fundamentale de cercetare din laborator pentru a fi utilizată în industrie va depinde de colaborările dintre cercetătorii universitari și industrie.
Astfel s-au obținut progrese remarcabile în sinteza și aplicațiile DFNS, iar DFNS pare să fi demonstrat un mare potențial ca o alternativă superioară materialelor silice convenționale, cum ar fi Stöber silica, MSN, MCM-41 și SBA-15, printre altele. Costul redus, activitatea înaltă și stabilitatea pronunțată a numeroaselor materiale pe bază de nanosilică fibroasă dendritică susțin argumentul nostru că această clasă de materiale va găsi o utilizare practică pentru o gamă largă de aplicații, de la cataliză până la captarea gazelor, de la recoltarea și depozitarea energiei la livrarea de medicamente , de la chimie analitică la remedierea mediului și multe altele.

Posted: Nov 03, 2017

Dendritic fibrous nanosilica: all-in-one nanomaterial for energy, environment and health

(Nanowerk News) Dendritic fibrous nanosilica (DFNS) attracted a great deal of attention in a large number of scientific disciplines such as catalysis, solar energy harvesting (photocatalysis, solar cells, etc.), energy storage, self-cleaning antireflective coatings, surface plasmon resonance (SPR)-based ultra-sensitive sensors, CO2 capture, and biomedical applications (drug delivery, protein and gene delivery, bioimaging, photothermal ablation, Ayurvedic and radiotherapeutics drug delivery, etc.).
applications for Dendritic fibrous nanosilica
Dendritic fibrous nanosilica (DFNS), also known as KCC-1, has a unique fibrous morphology and a high surface area with improved accessibility to the internal surface, tunable pore size and volume, controllable particle size, which made it useful in the fields of energy, environment, and health. (Image: Ayan Maity, Vivek Polshettiwar) (click on image to enlarge)
As discussed in this review (ChemSusChem, „Dendritic Fibrous Nanosilica for Catalysis, Energy Harvesting, Carbon Dioxide Mitigation, Drug Delivery, and Sensing”), the unique fibrous morphology of the DFNS family of materials bestows them with several important properties that were brilliantly exploited for use in a range of applications. The fibers of DFNS were functionalized with a range of organic groups, ionic liquids, organometallic complexes, polymers, peptides, enzymes, DNA, genes, etc. They were also loaded with metal nanoparticles, bi-metallic nanoparticles, even with single atoms of metals, quantum dots, and metal oxides and hydroxides. They were also used as hard templates for the synthesis of high surface area carbon with fibrous morphology. DFNS-based zeolites were also synthesized with unique activities.
DFNS provided a means to load large amount of catalytic active sites with exceptionally high accessibility compared to conventional mesoporous silica materials. Additionally, due to the radially oriented pores (channels), the size of which increased from the center of the sphere to its outer surface, reactants were able to easily access active sites within the channels, increasing their interaction with catalytic sites. This led to a multifold increase in their catalytic activity.
DFNS was cleverly used to develop novel photocatalysts by coating with γ-C3N4 and TiO2. The fibrous morphology of DFNS not only facilitated mass transfer and improved accessibility but also facilitated the formation of a uniform conformal coating and a high loading of semiconductors and guest molecules.
Notably, due to the fibrous structure of the material, the light harvesting properties of the catalyst were enhanced due multiple scattering effects and the reflection of a large amount of incident light. DFNS was also used to improve the performance of dye sensitized solar cells (DSSCs). In addition to energy harvesting, DFNS-coated carbon spheres were also used for energy storage using supercapacitors.
Functionalized DFNS, such as DFNS-amines and DFNS-oxynitrides, were successfully used to develop efficient CO2 sorbents, which could contribute in tackling the potentially dangerous climate change issue. Functionalized DFNS was also used to remove pollutants such as toxic metal ions, phosphorus, polyaromatic hydrocarbons, etc. from water bodies, which is a serious environmental concern.
DFFNS was efficiently used to deliver various anti-cancer drugs, and even the delivery of the Ayurvedic drug curcumin, DNA, genes and antimicrobial enzymes was achieved. In addition, a number of auxiliary functions were integrated into DFNS, such as stimuli responsiveness (light to thermal), fluorescence, radioactivity, anti-reflectance, superhydrophobicity, etc. This allows for their application in photothermal ablation therapy, real-time bioimaging, self-cleaning coatings, etc.
The sensing and quantification of pollutants was achieved using DFNS-based surface plasmon resonance (SPR). It was also used for an ultrasensitive enzyme-linked immunosorbent assay (ELISA+) with a 2000-fold enhancement in detection sensitivity.
DFNS seems like All-in-one-Nanomaterial and have huge potential for future development. Although DFNS has been gifted with excellent textural, physical and chemical properties and shows exceptional results in various applications, the evolution of DFNS from fundamental research studies in the laboratory to being used in industry will depend on collaborations between academic researchers and industry.
Thus, remarkable advances in the synthesis and applications of DFNS were achieved, and DFNS seems to have demonstrated great potential as a superior alternative to conventional silica materials such as Stöber silica, MSN, MCM-41, and SBA-15, among others. The low cost, high activity and pronounced stability of numerous dendritic fibrous nanosilica-based materials support our argument that this class of material will find practical use for a range of applications, from catalysis, to gas capture, from energy harvesting and storage to drug delivery, from analytical chemistry to environmental remediation and more.
Source: Tata Institute of Fundamental Research

O lume nouă de lumină ciudată(A strange new world of light)

au dezvoltat materiale nanostructurate care pot produce stări complet noi de lumină care prezintă comportament ciudat, cum ar fi îndoirea într-o spirală, tirbușirea și împărțirea ca o furculiță.

Posted: Nov 02, 2017

A strange new world of light

(Nanowerk News) There’s nothing new thing under the sun – except maybe light itself.
Over the last decade, applied physicists have developed nanostructured materials that can produce completely new states of light exhibiting strange behavior, such as bending in a spiral, corkscrewing and dividing like a fork.
These so-called structured beams not only can tell scientists a lot about the physics of light, they have a wide range of applications from super-resolution imaging to molecular manipulation and communications.
Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have developed a tool to generate new, more complex states of light in a completely different way.
Metasurface for Structured Light
A metasurface uses circularly polarized light to generate and control new and complex states of light, such swirling vortices of light. The new tool can be used to not only explore new states of light but also new applications for structured light. (Image: Second Bay Studio/Harvard SEAS)
The research is published in Science.
„We have developed a metasurface which is a new tool to study novel aspects of light,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the paper. „This optical component makes possible much more complex operations and allows researchers to not only explore new states of light but also new applications for structured light.”
The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.
The new metasurface connects two aspects of light, known as orbital angular momentum and circular polarization (or spin angular momentum). Polarization is direction along which light vibrates. In circularly polarized light, the vibration of light traces a circle. Think about orbital angular momentum and circular polarization like the motion of a planet. Circular polarization is the direction in which a planet rotates on its axis while orbital momentum describes how the planet orbits the sun.
The fact that light can even carry orbital momentum is a relatively recent discovery – only about 25 years old?– but it’s this property of light which produces strange new states, such as beams in the shape of corkscrews.
Swirling Vortex of Light
A metasurface can generate strange new beams of light that swirl and corkscrew. The black hole in the center of these vortices can be used to image features smaller than half a wavelength of light or move tiny molecules. (Image: Capasso Lab/Harvard SEAS)
Previous research has used the polarization of light to control the size and shape of these exotic beams but the connection was limited because only certain polarizations could convert to certain orbital momentums.
This research, however, significantly expands that connection.
„This metasurface gives the most general connection, through a single device, between the orbital momentum and polarization of light that’s been achieved so far,” said Robert Devlin, co-first author of the paper and former graduate student in the Capasso Lab.
The device can be designed so that any input polarization of light can result in any orbital angular momentum output – meaning any polarization can yield any kind of structured light, from spirals and corkscrews to vortices of any size. And, the multifunctional device can be programmed so that one polarization results in one vortex and a different polarization results in a completely different vortex.
„This is a completely new optical component,” said Antonio Ambrosio, Principal Scientist at Harvard Center for Nanoscale Systems (CNS) and co-first author of the paper. „Some metasurfaces are iterations or more efficient, more compact versions of existing optical devices but, this arbitrary spin-to-orbital conversion cannot be done with any other optical device. There is nothing in nature as well that can do this and produce these states of light.”
One potential application is in the realm of molecular manipulation and optical tweezers, which use light to move molecules. The orbital momentum of light is strong enough to make microscopic particles rotate and move.
„You can imagine, if we illuminate the device with one polarization of light, it will create a force of a particular kind,” said Ambrosio. „Then, if you want to change the force, all you need to do is change the polarization of the incoming light. The force is directly related to the design of the device.”
Another application is high-powered imaging. The black hole in the center of the vortex, known as the zero-light intensity region, can image features smaller than the diffraction limit, which is usually half of the wavelength of light. By changing the polarization of light, the size of this center region can be changed to focus different-sized features.
But these beams can also shed light on fundamental questions of physics.
„These particular beams are first and foremost of fundamental scientific interest,” said Noah Rubin, co-first author of the paper and graduate student in the Capasso Lab. „There is interest in these beams in quantum optics and quantum information. On the more applied side, these beams could find application in free-space optical communication, especially in scattering environments where this is usually difficult. Moreover, it has been recently shown that similar elements can be incorporated into lasers, directly producing these novel states of light. This may lead to unforeseen applications.”
Source: By Leah Burrows, Harvard John A. Paulson School of Engineering and Applied Sciences

Adăugarea filmelor subțiri CNT la țesături ar putea suporta electronice portabile(Addition of CNT thin-films to fabrics could power portable electronics)

Aceste două tipuri de materiale – numite p-type și picioare de tip n – sunt necesare pentru a genera suficientă putere într-un dispozitiv termoelectric. Polimerii polimerici, un alt material termoelectric organic studiat, produc în mod obișnuit materiale de tip n care funcționează mult mai rău decât omologii lor de tip p.
Faptul că filmele subțiri SWCNT pot face picioare de tip p și n de tip aceleași materiale cu performanțe identice înseamnă că curentul electric din fiecare picior este echilibrat în mod inerent, ceea ce ar trebui să simplifice fabricarea unui dispozitiv. Materialele cu cele mai performante performanțe au avut valori de performanță care depășesc materialele termoelectrice din materiale polimerice polimerice semiconductoare din materiale polimerice de ultimă oră.a declarat că introducerea SWCNT în țesături ar putea servi o funcție importantă pentru electronice personale „portabile”. Prin captarea căldurii corporale și transformarea acesteia în energie electrică, semiconductorul ar putea alimenta electronice portabile sau senzori încorporați în îmbrăcăminte.

Posted: Oct 31, 2017

Addition of CNT thin-films to fabrics could power portable electronics

(Nanowerk News) Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) reported significant advances in the thermoelectric performance of organic semiconductors based on carbon nanotube thin films that could be integrated into fabrics to convert waste heat into electricity or serve as a small power source.
The research demonstrates significant potential for semiconducting single-walled carbon nanotubes (SWCNTs) as the primary material for efficient thermoelectric generators, rather than being used as a component in a “composite” thermoelectric material containing, for example, carbon nanotubes and a polymer. The discovery is outlined in Energy & Environmental Science(„Large n- and p-type thermoelectric power factors from doped semiconducting single-walled carbon nanotube thin films”).
Two men stand in front of a screen that shows carbon nanotubes
NREL scientists Andrew Ferguson, left, and Jeffrey Blackburn stand in front of a screen displaying single-walled carbon nanotubes. (Photo by Dennis Schroeder/NREL)
“There are some inherent advantages to doing things this way,” said Jeffrey Blackburn, a senior scientist in NREL’s Chemical and Materials Science and Technology center and co-lead author of the paper with Andrew Ferguson. These advantages include the promise of solution-processed semiconductors that are lightweight and flexible and inexpensive to manufacture. Other NREL authors are Bradley MacLeod, Rachelle Ihly, Zbyslaw Owczarczyk, and Katherine Hurst. The NREL authors also teamed with collaborators from the University of Denver and partners at International Thermodyne, Inc., based in Charlotte, N.C.
Ferguson, also a senior scientist in the Chemical and Materials Science and Technology center, said the introduction of SWCNT into fabrics could serve an important function for “wearable” personal electronics. By capturing body heat and converting it into electricity, the semiconductor could power portable electronics or sensors embedded in clothing.
Blackburn and Ferguson published two papers last year on SWCNTs, and the new research builds on their earlier work. The first paper, in Nature Energy („Tailored Semiconducting Carbon Nanotube Networks with Enhanced Thermoelectric Properties”), showed the potential that SWCNTs have for thermoelectric applications, but the films prepared in this study retained a large amount of insulating polymer. The second paper, in ACS Energy Letters („Polymer-Free Carbon Nanotube Thermoelectrics with Improved Charge Carrier Transport and Power Factor”), demonstrated that removing this “sorting” polymer from an exemplary SWNCT thin film improved thermoelectric properties.
The newest paper revealed that removing polymers from all SWCNT starting materials served to boost the thermoelectric performance and lead to improvements in how charge carriers move through the semiconductor. The paper also demonstrated that the same SWCNT thin film achieved identical performance when doped with either positive or negative charge carriers.
These two types of material–called the p-type and the n-type legs, respectively–are needed to generate sufficient power in a thermoelectric device. Semiconducting polymers, another heavily studied organic thermoelectric material, typically produce n-type materials that perform much worse than their p-type counterparts.
The fact that SWCNT thin films can make p-type and n-type legs out of the same material with identical performance means that the electrical current in each leg is inherently balanced, which should simplify the fabrication of a device. The highest performing materials had performance metrics that exceed current state-of-the-art solution-processed semiconducting polymer organic thermoelectrics materials.
“We could actually fabricate the device from a single material,” Ferguson said. “In traditional thermoelectric materials you have to take one piece that’s p-type and one piece that’s n-type and then assemble those into a device.”
Source: National Renewable Energy Laboratory

Cercetătorii descoperă supraconductorul cu sări(Researchers discover superconductor with bounce)

a descoperit proprietăți extreme de „sări” sau super-elastice în memorie într-un material care ar putea fi aplicat pentru a fi utilizat ca dispozitiv de acționare în cele mai dure condiții, cum ar fi spațiul exterior și ar putea fi primul dintr – o nouă clasă de materiale cu memoria forme

Posted: Oct 23, 2017

Researchers discover superconductor with bounce

(Nanowerk News) The U.S. Department of Energy’s Ames Laboratory has discovered extreme “bounce,” or super-elastic shape-memory properties in a material that could be applied for use as an actuator in the harshest of conditions, such as outer space, and might be the first in a whole new class of shape memory materials (Nature Communications, „Superelasticity and Cryongenic Linear Shape Memory Effects of CaFe2As2„).
superconductor material
A single crystal of CaFe2As2 (scale bar 1 mm). Right: a micropillar of CaFe2As2, used to test its elasticity (scale bar 1 µm). (© NPG)
Shape-memory materials „remember” their original shape and return to it after they are deformed. They are commonly metallic alloys that make possible “unbreakable” eyeglass frames and quieter jet engines.
But the material in this research, CaFe2As2, is not a metallic alloy but an intermetallic more well-known for its novel superconducting properties. It has been so extensively studied that the team of researchers, from Ames Laboratory and the University of Connecticut, also made note of its high degree of pressure and strain sensitivity, and wondered about its possibilities as a structural material.
The researchers created micropillars of the material through single crystal growth followed by focused ion beam milling, and then subjected them to mechanical compression testing. They found a recoverable strain that can exceed 13 percent.
“This was a fantastic and gratifying result,” said Paul Canfield, a senior scientist at Ames Laboratory, and a Distinguished Professor and the Robert Allen Wright Professor of Physics and Astronomy at Iowa State University. “It fully confirmed our suspicions about CaFe2As2 offering a new mode of achieving superelastic effects and greatly expands the number of materials that may offer similar or even greater behavior.”
Source: Ames Laboratory