Lună: octombrie 2017

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

Aapetto Clip sistem de atașare rapidă / rapidă pentru dispozitive de transport cu plăcuțe tacâmuri tacticeSfast, Secure and Self-Cleaning(Aapetto Clip Quick-Attach/Quick-Release System for Tactical Armor Plate CarriersȘFast, Secure and Self-Cleaning)

Produsul este numit Aspetto Clip și este un sistem destul de ingenios de atașare rapidă / rapidă pentru purtătorii de tacâmuri tactile care sunt rapid, securizat și auto-curățați.ceilalți producători de plăci pentru utilizarea pe veste, dar nu suntem siguri de acest lucru

La cerere, imprimarea 3D a nanostructurilor plasmonice(On-demand 3D-printing of plasmonic nanostructures)

Structurile construite pe scara nanometrilor ar putea construi surse de lumină, senzori și calculatoare noi și îmbunătățite. Oamenii de stiinta au creat un nou mod de a imprima 3-D pe orice material sau forma fara masuratori costisitoare si consumatoare de timpMetoda de imprimare 3D generează nanomateriale personalizate, de la partea de sus în sus, la cerere. Tehnologia deschide calea către fabricarea mascată a arhitecturilor personalizate 1-, 2- și 3-D pe orice formă și material. Materialele pot avea comportamente plasmonice specifice. Oscilațiile oscilante codifică mai multe date decât este posibil cu tehnologiile convenționale. Astfel, acest avans poate accelera apariția unor noi surse de lumină, dispozitive de senzori și tehnologii de stocare ultra-densă a informațiilor.

Posted: Oct 22, 2017

On-demand 3D-printing of plasmonic nanostructures

(Nanowerk News) Structures built on the scale of nanometers could build new and improved light sources, sensors and computers. Scientists created a novel way to 3-D print on virtually any material or shape without costly and time-consuming masking steps (ACS Applied Materials & Interfaces, „Direct-write 3D nanoprinting of plasmonic structures”).
Focused electron beams are used to convert surface-bound molecules made from gold and carbon into the gas phase and deposit them to construct precise 3-D freestanding structures of pure gold
Focused electron beams are used to convert surface-bound molecules made from gold and carbon into the gas phase and deposit them to construct precise 3-D freestanding structures of pure gold. The ultra-sharp features produce free electron oscillations, or quasiparticles called plasmons, with high efficiency. (© ACS)
In a patterned sequence, researchers used a focused electron beam to dissociate surface-bound carbon- and metal-containing molecules and deposit them with precision. The result is a 3-D gold-carbon shape (shown here in a style reminiscent of Gandalf’s staff). They purified these structures in situ (inside the growth reactor) to remove carbon. They tested the resulting freestanding pure-gold architectures for plasmonic behavior—tiny, rapid waves of electron density created when light hits metal.
The 3-D printing approach produces customized, from the bottom up, nanostructures on demand. The technology paves the way to maskless fabrication of custom 1-, 2-, and 3-D architectures on virtually any material and surface shape. The materials can have specific plasmonic behaviors. Plasmonic oscillations encode more data than possible with conventional technologies. Thus, this advance may speed the advent of novel light sources, sensor devices and ultra-dense information storage technologies.
Structures on the scale of nanometers—much smaller than wavelengths of light—may improve transmission of plasmons, or small waves of electron density created when light hits an electron conductor, such as a metal.
To 3-D print nanoscale shapes with controlled properties, researchers integrated design, simulation and experiment. They used pattern sequencing to guide focused electron beams in inducing deposition of organometallic precursor molecules on a surface. Then, they removed residual carbon via in situ purification with water vapor to produce purely metallic freestanding 3-D nanostructures—an advance over previous 2-D nanoprinting with materials that contained significant carbon in addition to the desired metal. The structure that was produced—akin to the outline of up- and down-facing pyramids connected at their bases—demonstrated high plasmonic resonance at branches and tips.
On-demand 3-D printing can take place on virtually any material and surface shape, pushing nanoscale optical, mechanical, magnetic and even multifunctional materials beyond current limits and paving the way to functional plasmonic architectures for next-generation photonic, photovoltaic and data-storage technologies.
Source: Department of Energy, Office of Science

Nanoparticulele metalice vor ajuta la determinarea procentului de compuși volatili(Metallic nanoparticles will help to determine the percentage of volatile compounds)

Chimiștii ruși au inventat o tehnică care combină detecția optică utilizând benzi de testare pe hârtie cu nanoparticule triunghiulare de argint distribuite peste ele și extracție dinamică de gaze (extracția unui compus dintr-o soluție sau un amestec uscat prin intermediul gazelor lichefiate). Perspectivele acestei tehnici au fost demonstrate prin detectarea clorului. Clorul este adesea folosit pentru purificarea apei, deoarece distruge coaja exterioară a bacteriilor și a virușilor. Cu toate acestea, problema determinării concentrației de clor în apă rămâne relevantă, deoarece tehnicile existente nu sunt suficient de sensibile.

Posted: Oct 20, 2017

Metallic nanoparticles will help to determine the percentage of volatile compounds

(Nanowerk News) Researchers from the Faculties of Chemistry and of Materials Science of Lomonosov Moscow State University have developed a new way of increasing the sensitivity of detecting volatile compounds, especially chlorine, using metallic nanoparticles. The work has been published in the Talanta journal („Towards highly selective detection using metal nanoparticles: A case of silver triangular nanoplates and chlorine”).
TEM Micrograph of Aqueous Solution of Silver Triangular Nanoplates
This is an image of TEM micrograph of aqueous solution of silver triangular nanoplates. (Image: Aleksei Furletov)
Metallic nanoparticles, in particular the nanoparticles of gold and silver, are widely used in analytical chemistry. Amongst their uses is creating optical sensors based on the surface plasmonic resonance (the phenomenon of surface plasmon excitation by light) in colloidal solutions and on solid supports. Modern optical sensors have considerable advantages like high sensitivity, ease of detecting an analytic signal and adjustability of the optical and laboratory analysis parameters. Nevertheless, these devices have certain limitations when it comes to selectivity.
It happens because of aggregative instability of nanoparticles (the particles stick together when collide) which starts to happen during high ionic strength (high intensity of the electric field created by ions). The ion layer formed on the surface of particles is called the double electric layer and is characterized by an electrokinetic potential, also known as the zeta potential. With a decrease in the zeta potential, the electrostatic stabilization of nanoparticles does not happen.
The problem can be solved if the nanoparticles are attached to solid supports; scientists then acquire micro- or nanosensors based on solid particles. There are not many matrix materials for these sensors, and the process of attaching the nanoparticles to supports is not a simple one, so the researchers started working on a problem of modifying the surface of sensor matrices. For that goal they proposed separating the nanoparticles from ions and chemical compounds while retaining their sensitivity.
The Russian chemists invented a technique that combines optical detection using paper test strips with triangular silver nanoparticles spread over them, and dynamic gas extraction (the extraction of a compound from a solution or a dry mixture by means of liquefied gases). Perspectives of this technique were shown by detecting chlorine. Chlorine is often used to purify water, since it destroys the outer shell of bacteria and viruses. Nevertheless, the problem of determining the chlorine concentration in water remains relevant, since the existing techniques are not sensitive enough.
Aleksei Furletov, student of the Department of Analytic Chemistry, Faculty of Chemistry, Lomonosov Moscow State University, one of the paper’s authors, says: „The technique developed allows to determine small amounts of gaseous chlorine in the presence of large concentrations of foreign compounds without any sample preparation. This approach can be applied to other analytical systems based on metal nanoparticles, which opens up broad opportunities for the further development of this area of chemical analysis. „
Source: Lomonosov Moscow State University

Noile nano-panglici graphene conferă senzorilor o sensibilitate fără precedent(New graphene nano-ribbons lend sensors unprecedented sensitivity)

Pinning panglici de carbon de dimensiuni de ADN la un senzor de gaz poate spori sensibilitatea sale mult mai bine decat orice alt material cunoscut de carbon, spune un nou studiu de la Universitatea din Nebraska-Lincoln.
Echipa a dezvoltat o nouă formă de nano-panglică realizată din grafen, o fagure de 2-D de atomi de carbon. Atunci când cercetătorii au integrat un film al nano-panglicilor în circuitul unui senzor de gaz, acesta a răspuns de aproximativ 100 de ori mai sensibil la molecule decât au făcut senzorii cu cele mai performante materiale pe bază de carbon.

Posted: Oct 20, 2017

New graphene nano-ribbons lend sensors unprecedented sensitivity

(Nanowerk News) Pinning DNA-sized ribbons of carbon to a gas sensor can boost its sensitivity far better than any other known carbon material, says a new study from the University of Nebraska-Lincoln.
The team developed a new form of nano-ribbon made from graphene, a 2-D honeycomb of carbon atoms. When the researchers integrated a film of the nano-ribbons into the circuitry of a gas sensor, it responded about 100 times more sensitively to molecules than did sensors featuring even the best-performing carbon-based materials.
“We previously studied sensors based on other carbon-based materials such as graphene and graphene oxide,” said Alexander Sinitskii, associate professor of chemistry at Nebraska. “In the case of graphene nano-ribbons, we were certain that we would see some sensor response, but we did not expect that it would be that much higher than anything we have seen in the past.”
Reporting their findings in the journal Nature Communications („Laterally extended atomically precise graphene nanoribbons with improved electrical conductivity for efficient gas sensing”), the researchers showed that gas molecules can dramatically alter the electrical resistance of nano-ribbon films. Different gases produced varying resistance signatures, allowing the sensor to distinguish among them.
gas molecules widening the gaps between rows of graphene nano-ribbons
This rendering shows gas molecules widening the gaps between rows of the team’s graphene nano-ribbons. Nebraska’s Alexander Sinitskii and his colleagues have proposed that this phenomenon partly explains how the nano-ribbons grant sensors an unprecedented boost in sensitivity. (© Nature)
“With multiple sensors on a chip, we were able to demonstrate that we can differentiate between molecules that have nearly the same chemical nature,” said Sinitskii, a member of the Nebraska Center for Materials and Nanoscience. “For example, we can tell methanol and ethanol apart. So these sensors based on graphene nano-ribbons can be not only sensitive but also selective.”
Sinitskii and his colleagues suspect that the nano-ribbons’ remarkable performance stems partly from an unusual interaction between the ribbons and gas molecules. Unlike its predecessors, the team’s nano-ribbons — which resemble ordered rows of Charlie Brown’s shirt stripes — stand vertically rather than lying flat on a surface. The team has proposed that gas molecules can nudge these rows apart, effectively lengthening the gaps between nano-ribbons that electrons must jump to conduct electricity.

Enter the (benzene) ring
Graphene, whose 2004 discovery eventually earned a Nobel Prize, boasts unmatched electrical conductivity. But the material’s lack of a band gap — which requires electrons to gain energy before jumping from their near orbits around atoms to an outer “conduction band” that drives conductivity — initially prevented researchers from switching off that conductivity. This, in turn, posed challenges to applying graphene in electronics that require adjusting the material’s conductivity at will.
One potential solution involved trimming sheets of graphene down to nanoscopic ribbons that computer simulations suggested would possess the elusive band gap. This proved difficult to do with the atomic precision needed to preserve the properties that made graphene appealing in the first place, so researchers began fabricating ribbons from the bottom up by strategically snapping together molecules on certain types of solid surfaces. Though the process worked – and the resulting ribbons did have a band gap – it limited researchers to fabricating just a few ribbons at a time.
In 2014, Sinitskii pioneered an approach that could mass-produce nano-ribbons in a liquid solution, a vital step toward scaling up the technology for electronic applications. But the films made from these nano-ribbons were not conductive enough to perform electrical measurements. The team’s newest study adapted the original chemical approach by adding benzene rings — circular molecules with six atoms of both carbon and hydrogen — onto either side of a first-generation nano-ribbon. These rings widened the ribbon, reducing its band gap and enhancing its ability to conduct electricity.
“People do not often think of graphene nano-ribbons as a sensor material,” Sinitskii said. “However, the same (property) that makes the nano-ribbons good for devices such as transistors – the ability to change their conductivity by several orders of magnitude — is also what makes them good for sensors.
“It is possible to design many different kinds of graphene nano-ribbons with very diverse properties. Only a few types have been experimentally demonstrated so far, but there are many interesting theoretical predications about ribbons that are yet to be synthesized by chemists. So it is very likely that new nano-ribbons with even better sensor characteristics or other exciting properties will be developed in the near future.”
Source: By Scott Schrage, University of Nebraska-Lincoln

Un pas de stropire mai aproape de celulele solare mai ieftine(A sputtering step closer to cheaper solar cells)

Compoziția și proprietățile structurale ale stratului CZTS depind de procesul de depunere și de sulfurizare”, explică Dalapati. „Folosind o țintă cu un singur pas, am reușit să producem o peliculă subțire cu o compoziție uniformă și o suprafață netedă, care limitează formarea defectelor și este un proces foarte reproductibil”.
Cercetătorii au descoperit că cantitatea de molibden pierdută, denumită în continuare difuză, în timpul formării stratului MoSx a variat semnificativ odată cu schimbarea temperaturii de sulfurare și că eficiența globală a celulei solare a fost îmbunătățită de aproape cinci ori când temperatura de sulfurizare a fost crescut de la 500 la 600 de grade Celsius.
„Am obținut o eficiență solară de aproape cinci procente și vizează aproximativ 15% prin investigarea unui strat adecvat de tampon și interfață”, spune Dalapati.

Posted: Oct 19, 2017

A sputtering step closer to cheaper solar cells

(Nanowerk News) In the search for alternatives to silicon-based solar cells, A*STAR researchers are investigating a new material that is cheaper and easier to make, and could lead to better performing solar cells (Scientific Reports, „Impact of molybdenum out diffusion and interface quality on the performance of sputter grown CZTS based solar cells”).
Silicon solar cells are highly efficient, converting up to 25 per cent of sunlight into electricity, but fabricating the silicon wafers, which need to be around 300 microns thick to absorb all the sunlight that falls on them, is an expensive process that requires temperatures of around 1,200 degrees Celsius.
A cheaper alternative to silicon is cadmium telluride; however, it is highly toxic and known to cause cancer. This spurred Goutam Dalapati and colleagues from the A*STAR Institute of Materials Research & Engineering to investigate a copper-zinc-tin-sulfide (CZTS) compound, which offers the optical and electrical properties required in solar cells, but is made from non-toxic, widely available materials that are cheaper than silicon to process.
“CZTS is a semiconducting compound with a higher absorption coefficient than silicon,” says Dalapati, “so it’s able to absorb more visible light and produce more electricity than silicon, and can be used for very large-scale applications, like roofs and solar farms.”
Solar cells made from CZTS have potential for up to 30 per cent efficiency, but require high-quality, thin films of CZTS with no impurities, and a suitable material for the ‘buffer’ or interface layer that sits underneath the CZTS, helping to collect electrical charge.
A technique called quaternary sputtering was used to grow thin films of CZTS, where a single target made from CZTS was used as a source for depositing the film. This method offers several advantages over other deposition methods, including excellent uniformity over large areas and reduced reliance on toxic precursors. The researchers then investigated the effect of sulfurization temperature on the formation of a molybdenum sulfide (MoSx) interfacial layer.
“The composition and structural properties of the CZTS layer depend on the deposition process and the sulfurization,” explains Dalapati. “By using a single-step sputtering target we were able to produce a thin film with a uniform composition and smooth surface, which limits the formation of defects, and is a highly reproducible process.”
The researchers found that the amount of molybdenum lost, referred to as out-diffusing, during the MoS­x layer formation varied significantly with changes in sulfurization temperature, and that the overall efficiency of the solar cell was improved by nearly five times when the sulfurization temperature was raised from 500 to 600 degrees Celsius.
“We achieved a solar efficiency of nearly five per cent, and are aiming for around 15 per cent by investigating a suitable buffer and interface layer,” says Dalapati.
Source: A*STAR

Lupta extremă a luminii cu nanomateriale(Extreme light trapping with nanomaterials)

Pentru a manipula fluxul de lumină vizibilă, cu lungimi de undă variind de la 400 la 700 nanometri, Lin pionier o metoda de construire a unui cub perfect simetrice de nanotuburi pentru a se potrivi scara luminii. Mai întâi, un strat de dioxid de titan este depus pe un substrat. Apoi, un strat subțire de dioxid de crom este depus pentru a servi ca o mască pentru un proces fotolitografic care leșcă linii în dioxid de titan. Odată finalizată, se folosește un solvent pentru a elimina dioxidul de crom rămase, completând primul strat de „log.“ Pentru a construi straturi suplimentare, un strat de dioxid de siliciu este depozitat pentru a umple cavitățile dintre buștenii, suprafața este lustruită plat la partea superioară a primului strat și întregul proces este repetat la un unghi precis de 90 de grade față de primul strat.
Un strat de material este mai mic de 1 milion de un metru – sau micron – gros, dar a fost produs în plafoane de 100 milimetri lățime, dând materialului de 100.000 de ori spațiul pentru a absorbi lumina.a construit o nanostructură a cărei latură de cristal îndoaie lumina când intră în material și o direcționează într-o cale paralelă cu suprafața , cunoscută ca „refracție paralelă cu interfața”. Structura este construită din nanotuburi suprapuse și seamănă cu o rețea tridimensională din Lincoln Logs. Nano-cristalele fotonice construite folosind procesul său permit „capturarea luminoasă” extremă și ar putea avea aplicații de la celulele solare subțiri la funcții fotochimice cum ar fi detectarea și împărțirea apei.

Posted: Oct 19, 2017

Extreme light trapping with nanomaterials

(Nanowerk News) A silicon solar cell harvests the energy of the sun as light travels down through light-absorbent silicon. To reduce weight and cost, solar cells are thin, and while silicon absorbs visible light well, it captures less than half of the light in the near-infrared spectrum, which makes up one-third of the sun’s energy. The depth of the material limits absorption. But what if light within the cell could be channeled horizontally so that silicon could absorb its energy along the width of the cell rather than its depth?
With such an advance in mind, Shawn-Yu Lin, professor of physics, applied physics, and astronomy at Rensselaer Polytechnic Institute, has built a nanostructure whose crystal lattice bends light as it enters the material and directs it in a path parallel to the surface, known as “parallel to interface refraction.” The structure is built of overlapping nanotubes and resembles a three-dimensional grid made of Lincoln Logs. Photonic nanocrystals built using his process enable extreme “light trapping” and could have applications from thin-film solar cells to photo-chemical functions like sensing and water splitting.
Light from quadrant I usually refracts within quadrant III. But in parallel to interface refraction, the light is bent into quadrant IV
Light from quadrant I usually refracts within quadrant III. But in parallel to interface refraction, the light is bent into quadrant IV. (Image: Rensselaer Polytechnic Institute)
“These results prove that this effect exists, that if you follow my guidelines of simple cubic symmetry, you can bend light by 90 degrees. The photonic crystal forces light to bend in a deterministic manner, rather than random scattering or surface effects,” said Lin. “This is a new type of light-matter interaction that lies at the heart of what light trapping is intended to do.”
In experimental results, which appear in Nature Scientific Reports („Effectively infinite optical path-length created using a simple cubic photonic crystal for extreme light trapping”), Lin created a photonic crystal using titanium dioxide, a material with weak visible light absorption, to prove the success of the effect. Results using a 900-nanometer thick titanium dioxide photonic nanocrystal showed absorption enhanced by one to two orders of magnitude greater than a reference film of the same material for some regions. Lin built the nanocrystal – first in silicon, now in titanium dioxide – based on the theoretical predictions of his collaborator, Sajeev John, a physicist at the University of Toronto.
Light trapping describes the process of confining light to a given space, usually with the intent of converting it to other forms of energy. In one approach, materials are designed to slow light, so that it spends more time in the material. In the approach Lin used, the light is bent away from its given path, making it travel a longer distance within the material, in this case, the full width of a titanium dioxide wafer.
Light always bends somewhat as it enters a material with a different optical index, something easily seen as light enters water. In water, and many other materials, the light bends only slightly. The arrangement of atoms in the titanium dioxide crystal Lin created matches the scale of visible light wavelengths, scattering light at multiple points in space simultaneously as it moves into the lattice. As a consequence, light cannot move as it does through space or any continuous medium. Instead, it is bent at an obtuse angle – a phenomenon known as “negative refraction” – and channeled along the width of the material.
To manipulate the flow of visible light, with wavelengths ranging from 400 to 700 nanometers, Lin pioneered a method of building a perfectly symmetrical cube of nanotubes to match the scale of the light. First, a layer of titanium dioxide is deposited on a substrate. Then, a thin layer of chromium dioxide is deposited to serve as a mask for a photolithographic process that etches lines into the titanium dioxide. Once completed, a solvent is used to remove the remaining chromium dioxide, completing the first layer of “logs.” To build additional layers, a layer of silicon dioxide is deposited to fill the cavities between the logs, the surface is polished flat to the top of the first layer, and the entire process is repeated at a precise 90-degree angle from the first layer.
One layer of the material is less than 1 millionth of a meter – or micron – thick, but was produced in wafers 100 millimeters wide, giving the material as much as 100,000 times the space to absorb light.
“This discovery proves a huge enhancement in path length when using a material that has a very low absorption. Its discovery changes the name of the game from vertically absorbed, to horizontally absorbed in a super thin structure,” said Lin.
Source: Rensselaer Polytechnic Institute

Lupta extremă a luminii cu nanomateriale(Extreme light trapping with nanomaterials)

obtuz – un fenomen cunoscut ca „refracție negativă” – și canalizat de-a lungul lățimii materialului.
Pentru a manipula fluxul de lumină vizibilă, cu lungimi de undă cuprinse între 400 și 700 nanometri, Lin a inițiat o metodă de construire a unui cub perfect simetric de nanotuburi, pentru a se potrivi cu scara luminii. Mai întâi, un strat de dioxid de titan este depus pe un substrat. Apoi, un strat subțire de dioxid de crom este depus pentru a servi ca o mască pentru un proces fotolitografic care leșcă linii în dioxid de titan. Odată finalizat, se folosește un solvent pentru a îndepărta dioxidul de crom rămas, finalizând primul strat de „busteni”. Pentru a construi straturi suplimentare, se depune un strat de dioxid de siliciu pentru a umple cavitățile între bușteni, suprafața este lustruită partea superioară a primului strat și întregul proces este repetat la un unghi precis de 90 de grade față de primul strat.
Un strat de material este mai mic de 1 milion de un metru – sau micron – gros, dar a fost produs în plafoane de 100 milimetri lățime, dând materialului de 100.000 de ori spațiul pentru a absorbi lumina.

Posted: Oct 19, 2017

Extreme light trapping with nanomaterials

(Nanowerk News) A silicon solar cell harvests the energy of the sun as light travels down through light-absorbent silicon. To reduce weight and cost, solar cells are thin, and while silicon absorbs visible light well, it captures less than half of the light in the near-infrared spectrum, which makes up one-third of the sun’s energy. The depth of the material limits absorption. But what if light within the cell could be channeled horizontally so that silicon could absorb its energy along the width of the cell rather than its depth?
With such an advance in mind, Shawn-Yu Lin, professor of physics, applied physics, and astronomy at Rensselaer Polytechnic Institute, has built a nanostructure whose crystal lattice bends light as it enters the material and directs it in a path parallel to the surface, known as “parallel to interface refraction.” The structure is built of overlapping nanotubes and resembles a three-dimensional grid made of Lincoln Logs. Photonic nanocrystals built using his process enable extreme “light trapping” and could have applications from thin-film solar cells to photo-chemical functions like sensing and water splitting.
Light from quadrant I usually refracts within quadrant III. But in parallel to interface refraction, the light is bent into quadrant IV
Light from quadrant I usually refracts within quadrant III. But in parallel to interface refraction, the light is bent into quadrant IV. (Image: Rensselaer Polytechnic Institute)
“These results prove that this effect exists, that if you follow my guidelines of simple cubic symmetry, you can bend light by 90 degrees. The photonic crystal forces light to bend in a deterministic manner, rather than random scattering or surface effects,” said Lin. “This is a new type of light-matter interaction that lies at the heart of what light trapping is intended to do.”
In experimental results, which appear in Nature Scientific Reports („Effectively infinite optical path-length created using a simple cubic photonic crystal for extreme light trapping”), Lin created a photonic crystal using titanium dioxide, a material with weak visible light absorption, to prove the success of the effect. Results using a 900-nanometer thick titanium dioxide photonic nanocrystal showed absorption enhanced by one to two orders of magnitude greater than a reference film of the same material for some regions. Lin built the nanocrystal – first in silicon, now in titanium dioxide – based on the theoretical predictions of his collaborator, Sajeev John, a physicist at the University of Toronto.
Light trapping describes the process of confining light to a given space, usually with the intent of converting it to other forms of energy. In one approach, materials are designed to slow light, so that it spends more time in the material. In the approach Lin used, the light is bent away from its given path, making it travel a longer distance within the material, in this case, the full width of a titanium dioxide wafer.
Light always bends somewhat as it enters a material with a different optical index, something easily seen as light enters water. In water, and many other materials, the light bends only slightly. The arrangement of atoms in the titanium dioxide crystal Lin created matches the scale of visible light wavelengths, scattering light at multiple points in space simultaneously as it moves into the lattice. As a consequence, light cannot move as it does through space or any continuous medium. Instead, it is bent at an obtuse angle – a phenomenon known as “negative refraction” – and channeled along the width of the material.
To manipulate the flow of visible light, with wavelengths ranging from 400 to 700 nanometers, Lin pioneered a method of building a perfectly symmetrical cube of nanotubes to match the scale of the light. First, a layer of titanium dioxide is deposited on a substrate. Then, a thin layer of chromium dioxide is deposited to serve as a mask for a photolithographic process that etches lines into the titanium dioxide. Once completed, a solvent is used to remove the remaining chromium dioxide, completing the first layer of “logs.” To build additional layers, a layer of silicon dioxide is deposited to fill the cavities between the logs, the surface is polished flat to the top of the first layer, and the entire process is repeated at a precise 90-degree angle from the first layer.
One layer of the material is less than 1 millionth of a meter – or micron – thick, but was produced in wafers 100 millimeters wide, giving the material as much as 100,000 times the space to absorb light.
“This discovery proves a huge enhancement in path length when using a material that has a very low absorption. Its discovery changes the name of the game from vertically absorbed, to horizontally absorbed in a super thin structure,” said Lin.
Source: Rensselaer Polytechnic Institute

Separarea metanului și a CO2 va deveni mai eficientă(Separating methane and CO2 will become more efficient)

Cercetătorii de la KU Leuven (Universitatea din Leuven), Belgia, au dezvoltat o nouă membrană care face procesul de separare mult mai eficient ( Energy & Environmental Science , „Membrană selectivă de separare a gazelor cu ajutorul structurilor organice metalice amorficate in situ” ).
Aceasta conferă noii membrane cea mai mare selectivitate raportată vreodată, prevenind în același timp plastificarea atunci când concentrația de CO 2 este ridicată. „Dacă începe cu un 50/50 de CO 2 / amestec de metan, această membrană vă oferă 164 de ori mai mult CO 2 decât metan după permeabilitatea prin membrana“ , explica Dr. Lik Hong Wee. „Acestea sunt cele mai bune rezultate înregistrate vreodată în literatura științifică.”

Posted: Oct 18, 2017

Separating methane and CO2 will become more efficient

(Nanowerk News) To make natural gas and biogas suitable for use, the methane has to be separated from the CO2. This involves the use of membranes: filters that stop the methane and let the CO2 pass through. Researchers at KU Leuven (University of Leuven), Belgium, have developed a new membrane that makes the separation process much more effective (Energy & Environmental Science, „Highly selective gas separation membrane using in situ amorphised metal–organic frameworks”).
When it comes to extracting natural gas or producing biogas, it’s all about the methane. But methane is never found in its pure form. Natural gas, for instance, always contains quite a bit of carbon dioxide (the greenhouse gas CO2), sometimes up to 50 percent. To purify the methane – or, in other words, remove the CO2 – the industry often uses membranes. These membranes function as molecular sieves that separate the methane and the CO2. The methane can then be used as a source of energy for heating, for the production of chemicals, or as fuel, while the CO2can be reused as a building block for renewable fuels and chemicals.
New Membrane Makes Separation of Methane and C02 More Efficient
Natural gas or biogas always needs to be purified before use. First, the methane molecules (in black and white) are separated from the CO2 molecules (in red and black) by means of membranes with tiny pores through which only the CO2 can pass. After the purification process, the methane can be used as fuel, for heating, or for the production of chemicals. (Image: KU Leuven – Verbeke)
Existing membranes still need to be improved for effective CO2 separations, says Professor Ivo Vankelecom from the KU Leuven Faculty of Bioscience Engineering. „An effective membrane only allows the CO2 to pass through, and as much of it as possible. The commercially available membranes come with a trade-off between selectivity and permeability: they are either highly selective or highly permeable. Another important problem is the fact that the membranes plasticise if the gas mixture contains too much CO2. This makes them less efficient: almost everything can pass through them, so that the separation of methane and CO2 fails.”
The best available membranes consist of a polymeric matrix with a filler in it, for instance a metal-organic framework (MOF). This MOF filler has nanoscale pores. The new study has shown that the characteristics of such a membrane improve significantly with a heat treatment above 160 degrees Celsius during the production process. „You get more crosslinks in the polymeric matrix: the net densifies, so to speak, and that in itself already improves the membrane performance, because it can no longer plasticise. At these temperatures, the structure of the MOF – the filler – changes, and it becomes more selective. Finally, the high-temperature treatment also improves polymer-filler adhesion: the gas mixture can no longer escape through little holes at the filler-polymer interface.”
This gives the new membrane the highest selectivity ever reported, while preventing plasticisation when the concentration of CO2 is high. „If you start off with a 50/50 CO2/methane mixture, this membrane gives you 164 times more CO2 than methane after permeation through the membrane,” Dr Lik Hong Wee explains. „These are the best results ever reported in scientific literature.”
Source: KU Leuven

Un nou material pentru amintirile digitale ale viitorului(New material for digital memories of the future)

a dezvolta primul material cu proprietăți de conductivitate care pot fi pornite și oprite folosind polarizarea feroelectrică.Fenomenul poate fi folosit pentru memorii digitale mici și flexibile ale viitorului și pentru tipuri complet noi de celule solare.

Posted: Oct 18, 2017

New material for digital memories of the future

(Nanowerk News) Professor Martijn Kemerink of Linköping University has worked with colleagues in Spain and the Netherlands to develop the first material with conductivity properties that can be switched on and off using ferroelectric polarisation.
The phenomenon can be used for small and flexible digital memories of the future, and for completely new types of solar cells.
In an article published in the prestigious scientific journal Science Advances („Ferroelectric self-assembled molecular materials showing both rectifying and switchable conductivity”), the research group shows the phenomenon in action in three specially built molecules, and proposes a model for how it works.
material with conductivity properties that can be switched on and off using ferroelectric polarisation
The first material with conductivity properties that can be switched on and off using ferroelectric polarisation. (Image: Thor Balkhed)
“I originally had the idea many years ago, and then I just happened to meet Professor David González-Rodríguez, from the Universidad Autónoma de Madrid, who had constructed a molecule of exactly the type we were looking for,” says Martijn Kemerink.
The organic molecules that the researchers have built conduct electricity and contain dipoles. A dipole has one end with a positive charge and one with a negative charge, and changes its orientation (switches) depending on the voltage applied to it.
In a thin film of the newly developed molecules, all the dipoles can be caused to switch at exactly the same time, which means that the film changes its polarisation. The property is known as ferroelectricity. In this case, it also leads to a change in the conductivity, from low to high or vice versa. When an electrical field with the opposite polarity is applied, the dipoles again switch direction. The polarisation changes, as does the ability to conduct current.
The molecules designed according to the model developed by the LiU researchers tend to spontaneously place themselves on top of each other to form a stack or a supramolecular wire, with a diameter of just a few nanometres. These wires can subsequently be placed into a matrix in which each junction constitutes one bit of information. This will make it possible in the future to construct extremely small digital memories with very high information density. The synthesis of the new molecules is, however, still too complicated for practical use.
“We have developed a model for how the phenomenon arises in principle, and we have shown experimentally that it works for three different molecules. We now need to continue work to build molecules that can be used in practical applications,” says Professor Martijn Kemerink, from Complex Materials and Devices at Linköping University, and principal author of the article.
Source: Linköping Universitet