Categorie: Materiale noi cu structura compozita

Materialul hibrid strălucește ca meduzele(Hybrid material glows like jellyfish)

au proiectat si construit un material care imita procesul ( ACS Nano , „Transferul de energie de rezonanta de biotinism in proba in nanostructuri cuantice-luciferaza” ).
Materialul combină tije mici, sintetice și enzime naturale. În combinație corectă, aceste materiale produc lumină. Adică materialul strălucește roșu când este stimulat chimic. Se urmează un proces similar celui din meduze.

Posted: Oct 23, 2017

Hybrid material glows like jellyfish

(Nanowerk News) Jellyfish get their beautiful, greenish-blue glow from a chemical reaction. Inspired by this natural process, scientists from Syracuse University designed and built a material that mimics the process (ACS Nano, „Probing bioluminescence resonance energy transfer in quantum rod–luciferase nanoconjugates”).
The material combines tiny, synthetic rods and natural enzymes. Combined correctly, these materials yield light. That is, the material glows red when chemically stimulated. It follows a process similar to that in jellyfish.
hybrid composite nanomaterial design inspired by nature
Hybrid composite nanomaterial design inspired by nature. Inspired by the biological resonance energy transfer (BRET) mechanism that jellyfish use to convert blue luminescence to green and generate their distinctive glow (top), scientists have designed enzyme/nanorod hybrid nanomaterials (bottom) that glow red upon chemical stimulation. (Image: Center for Functional Nanomaterials, Brookhaven National Laboratory)
The material produces light without batteries or wall plugs. It shows how to control a bioluminescence process. Detailed analysis of the material offered insight into turning chemical energy into light more efficiently.
Improving the efficiency of nanoscale energy transfer in quantum dot or quantum rod based systems requires the ability to fine tune variables influencing this process, such as the distance between donor and acceptor, stoichiometry, and donor and acceptor spectral overlap.
In most energy transfer cases, quantum dots or rods are used as donors because they efficiently harvest light with broad absorption extending to ultraviolet wavelengths. In this study, scientists created a nanohybrid biotic-abiotic system inspired by nature’s bioluminescent energy transfer (BRET) process.
In BRET, the donor is a biomolecule that undergoes chemical stimulation, leading to bioluminescence, which is then transferred to an acceptor biomolecule that emits light. Scientists chose as the donor a luciferase enzyme that emits green light following chemical stimulation and the acceptor as a core-shell nanocrystal designed to absorb and emit in the red spectral region.
The results allowed the research team to elucidate the design parameters needed to improve BRET efficiency and to understand the underlying BRET mechanism by the use of a biotic-abiotic nanohybrid system.
Source: Department of Energy, Office of Science

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

O soluție cadru metalică-organică pentru stocarea energiei regenerabile(A metal-organic framework solution for storing renewable energy)

au folosit o structură metalică organică bazată pe cobalt, care a imitat conductivitatea unui metal și a unui semiconductor la diferite temperaturi. Cadrul metalic-organic creat de oamenii de știință a demonstrat cea mai mare conductivitate la temperaturi foarte scăzute și foarte ridicate.

Posted: Oct 12, 2017

A metal-organic framework solution for storing renewable energy

(Nanowerk News) Scientists have long searched for the next generation of materials that can catalyze a revolution in renewable energy harvesting and storage.
One candidate appears to be metal-organic frameworks. Scientists have used these very small, flexible, ultra-thin, super-porous crystalline structures to do everything from capturing and converting carbon into fuels to storing hydrogen and other gases. Their biggest drawback has been their lack of conductivity.
Now, according to USC scientists, it turns out that metal-organic frameworks can conduct electricity in the same way metals do.
A Conductive Metal-organic Framework
The cobalt-based metal-organic framework used by the USC scientists, with purple representing cobalt, yellow representing sulfur and gray representing carbon. (Image: Smaranda Marinescu)
This opens the door for metal organic-frameworks to one day efficiently store renewable energy at a very large, almost unthinkable scale.
„For the first time ever, we have demonstrated a metal-organic framework that exhibits conductivity like that of a metal. The natural porosity of the metal-organic framework makes it ideal for reducing the mass of material, allowing for lighter, more compact devices” said Brent Melot, assistant professor of chemistry at the USC Dornsife College of Letters, Arts & Sciences.
„Metallic conductivity in tandem with other catalytic properties would add to its potential for renewable energy production and storage” said Smaranda Marinescu, assistant professor of chemistry at the USC Dornsife College.
Their findings were published in the Journal of the American Chemical Society („Metallic Conductivity in a Two-Dimensional Cobalt Dithiolene Metal–Organic Framework”).

An emerging catalyst for long-term renewable energy storage
Metal-organic frameworks are so porous that they are well-suited for absorbing and storing gases like hydrogen and carbon dioxide. Their storage is highly concentrated: 1 gram of surface area provides the equivalent of thousands of square feet in storage.
Solar has not yet been maximized as an energy source. The earth receives more energy from one hour of sunlight than is consumed in one year by the entire planet, but there is currently no way to use this energy because there is no way to conserve all of it. This intermittency is intrinsic to nearly all renewable power sources, making it impossible to harvest and store energy unless, say, the sun is shining or the wind is blowing.
If scientists and industries could one day regularly reproduce the capability demonstrated by Marinescu, it would go a long way to reducing intermittency, allowing us to finally make solar energy an enduring and more permanent resource.

Metal or semiconductor: why not both?
Metal-organic frameworks are two-dimensional structures that contain cobalt, sulfur, and carbon atoms. In many ways, they very broadly resemble something like graphene, which is also a very thin layer of two-dimensional, transparent material.
As temperature goes down, metals become more conductive. Conversely, as the temperature goes up, it is semiconductors that become more conductive.
In the experiments run by Marinescu’s group, they used a cobalt-based metal-organic framework that mimicked the conductivity of both a metal and semiconductor at different temperatures. The metal-organic framework designed by the scientists demonstrated its greatest conductivity at both very low and very high temperatures.
Source: University of Southern California

„Armura lichidă” îngreunează articolele de salvare(‘Liquid armor’ toughens spacesuits)

Fluidele de îngroșare prin forfecare permează țesăturile și straturile de material cu o tehnologie remarcabilă, care devine efectiv mai puternică atunci când este lovită cu o forță crescândă, ceea ce face ca materialul să fie puternic pătruns și rezistent la balistice. La fel de uimitor, materialul adăugat nanocompozit, denumit uneori „armură lichidă”, dar marcat ca STF-Armor, adaugă o greutate redusă materialului și nu reduce flexibilitatea acestuia – două caracteristici critice pentru un costum de spațiu.aplicate habitatelor spațioase gonflabile, precum și echipamente de protecție, echipamente de luptă împotriva incendiilor și de aplicare a legii, mănuși industriale și costume de hazmat

Posted: Oct 12, 2017

‘Liquid armor’ toughens spacesuits

(Nanowerk News) Astronauts are a smart, courageous and resilient lot, no doubt about that. But when they go out for a walk in space – in environments none of us could survive on our own – they need a lot of protection.
There are plenty of perilous possibilities. One of the most serious threats is the stuff flying around in space – sharp stuff, dusty stuff, fast-moving stuff.
Puncture an astronaut’s space suit – whether by projectile, the sharp edge of a tool or falling onto a rock – and you could let in a world of trouble.
space suit material
‘Liquid armor” developed at the University of Delaware can be painted on fabric, making the textile extremely difficult to puncture. (Image: University of Delaware)
NASA sees great promise in a new protective textile – the shear thickening fluid technology co-developed at the University of Delaware by Norman Wagner, Unidel Robert L. Pigford Chair in Chemical and Biomolecular Engineering, and STF Technologies, the company he co-founded with UD alum Richard Dombrowski.
Shear thickening fluids permeate fabrics and layers of material with a remarkable technology that actually gets stronger when it is struck with increasing force, making the material highly puncture and ballistic-resistant. Just as amazing, the added nanocomposite material, sometimes called „liquid armor,” but trademarked as STF-Armor, adds little weight to the fabric and does not reduce its flexibility – two critical features for a space suit.
After proving its mettle with support from a NASA Small Business Innovation Research Phase 1 contract, STF Technologies has won a $750,000 Small Business Technology Transfer Research Phase II grant to produce a prototype that will shield astronauts whether they are in low-earth orbit – as they are at the International Space Station – on the moon or stepping onto Mars.
That project has many benefits for ongoing work, too, including development of the Z2 spacesuit for NASA’s Journey to Mars mission. UD’s Center for Composite Materials has been integral to that effort, providing innovative components for the overall design created by ILC Dover.
„It’s the same overall suit, but different aspects of it,” said Wagner, who has worked extensively with CCM. „They’re separate projects but both are related to making the suit better.”
Wagner, a fellow in the National Academy of Inventors, was co-author of three presentations at the recent International Space Station Research & Development Conference in Washington D.C., including discussion of experiments his lab will do on the ISS and ways STF-Armor could be applied to inflatable space habitats as well as protective equipment, firefighting and law enforcement gear, industrial gloves and hazmat suits. With UD Prof. Christopher Kloxin (chemical & biomolecular engineering, materials science & engineering) and UD alum Melissa Gordon (now on the faculty at Lafayette College), Wagner explained recent advances with „self-healing” materials.
Near-future plans include launching STF’s materials on a November trip to the ISS, where it will be placed outside the space station for a year and then analyzed to see how it fares in that environment.
Undergraduates will have opportunity to be part of STF Technologies’ work through the Office of Economic Innovation and Partnership’s Spin-In Program, a popular and successful collaboration between UD students and business entrepreneurs who need their engineering, business or policy savvy.
„NASA funding for small-business development has an expectation that space technology will have earth-based benefits, and they generally do,” Wagner said.
The project brings many layers of innovation together – linking NASA’s missions with the research and innovation produced by Wagner and other researchers and giving students and business owners opportunity to contribute to significant projects, gaining invaluable experience.
„Human exploration of space inspires people to do great things,” Wagner said. „And it attracts a lot of interesting, good people.”
Source: University of Delaware

Injectarea electronilor distruge structura 2D în noul model atomic(Injectarea electronilor distruge structura 2D în noul model atomic)

Ideea dopajului de electroni pentru a modifica strucCercetatorii au folosit ditelluri de molibden (MoTe 2 ), un semiconductor tipic 2-D, si au acoperit-o cu un lichid ionic (DEME-TFSI), care are o capacitate ultra-mare sau capacitatea de a stoca incarcatura electrica. Stratul de lichid ionic a permis cercetătorilor să injecteze semiconductorul cu electroni la o densitate de o sută de bilioane la un cvadrilioane pe centimetru pătrat. Este o densitate de electroni care este una-două ordine mai mare decât cea care ar putea fi obținută în materialele 3-D în vrac, au spus cercetătorii.tura atomică a materialului este unică pentru materialele 2-D, care sunt mult mai ușor de reglabil electric în comparație cu materialele în vrac 3-D”,

Postat: 11 octombrie 2017

Injectarea electronilor distruge structura 2D în noul model atomic

( Nanowerk News ) Aceeași încărcătură electrostatică care poate face ca părul să stea pe capăt și să atragă baloane la îmbrăcăminte ar putea fi o modalitate eficientă de a conduce vehicule subțiri subțiri cu memorie electronică ale viitorului, potrivit unui nou studiu condus de cercetători de la Departamentul Energiei Lawrence Laboratorul Național Berkeley (Laboratorul Berkeley).
Intr-un studiu publicat astazi in revista Nature ( „Transformarea fazei structurale in monostratul MoTe 2 condus de dopajul electrostatic” ), oamenii de stiinta au gasit o modalitate de a schimba in mod reversibil structura atomica a unui material 2-D prin injectare sau „doping” cu electroni.Procesul utilizează mult mai puțină energie decât metodele curente pentru a schimba configurația structurii unui material.
chematic prezintă configurația pentru tranziția de fază structurală pe un monostrat de molibden ditelluride (MoTe2, prezentat ca sfere galbene și albastre), ancorat de un electrod metalic (poarta de sus și sol)
Schema prezintă configurația pentru tranziția fazei structurale pe un monostrat de molibden ditelluride (MoTe 2 , prezentat ca sfere galbene și albastre), care este ancorat de un electrod metalic (poarta de sus și sol). Lichidul ionic care acoperă monostratul și electrozii permite o densitate mare de electroni să populeze monostratul, ceea ce duce la modificări ale laturii structurale de la un model hexagonal (2H) la un monoclinic (1T ‘). (Credit: Ying Wang / Berkeley Lab)
„Arătăm pentru prima dată că este posibil să se injecteze electroni pentru a conduce schimbări de fază structurală în materiale”, a declarat cercetătorul principal al studiului, Xiang Zhang, om de știință de la Facultatea de Materiale Berkeley Lab și profesor la UC Berkeley. „Prin adăugarea de electroni într-un material, energia totală urcă și va sfârși balanța, rezultând structura atomică rearanjând un nou model care este mai stabil. O astfel de tranziție a fazei structurale determinată de dopajul electronic la limita 2-D nu este importantă numai în fizica fundamentală; de asemenea, deschide ușa pentru noua memorie electronică și comutarea la putere redusă în următoarea generație de dispozitive ultra-subțiri. „
Comutarea configurației structurale a unui material de la o fază la alta este caracteristica fundamentală, binară care stă la baza circuitelor digitale actuale. Componentele electronice capabile de această tranziție de fază s-au diminuat până la dimensiuni subțiri de hârtie, dar ele sunt încă considerate a fi vrac, straturi 3D de către oamenii de știință. Prin comparație, materialele monostrat 2-D sunt compuse dintr-un singur strat de atomi sau molecule a căror grosime este de 100.000 de ori mai mică decât părul uman.
„Ideea dopajului de electroni pentru a modifica structura atomică a materialului este unică pentru materialele 2-D, care sunt mult mai ușor de reglabil electric în comparație cu materialele în vrac 3-D”, a declarat co-lead autorul Jun Xiao, student în laboratorul Zhang .
Abordarea clasică de a conduce tranziția structurală a materialelor implică încălzirea la peste 500 de grade Celsius. Astfel de metode sunt intensive din punct de vedere energetic și nu sunt fezabile pentru aplicații practice. În plus, căldura în exces poate reduce semnificativ durata de viață a componentelor în circuitele integrate.
Un număr de grupuri de cercetare au investigat, de asemenea, utilizarea substanțelor chimice pentru a modifica configurația atomilor din materialele semiconductoare, dar acest proces este încă dificil de controlat și nu a fost adoptat pe scară largă de către industrie.
„Aici folosim dopajul electrostatic pentru a controla configurația atomică a unui material bidimensional”, a declarat co-autorul studiului Ying Wang, un alt student absolvent în laboratorul lui Zhang. „În comparație cu utilizarea substanțelor chimice, metoda noastră este reversibilă și fără impurități. Are un potențial mai mare de integrare în fabricarea de telefoane mobile, computere și alte dispozitive electronice”.
Cercetatorii au folosit ditelluri de molibden (MoTe 2 ), un semiconductor tipic 2-D, si au acoperit-o cu un lichid ionic (DEME-TFSI), care are o capacitate ultra-mare sau capacitatea de a stoca incarcatura electrica. Stratul de lichid ionic a permis cercetătorilor să injecteze semiconductorul cu electroni la o densitate de o sută de bilioane la un cvadrilioane pe centimetru pătrat. Este o densitate de electroni care este una-două ordine mai mare decât cea care ar putea fi obținută în materialele 3-D în vrac, au spus cercetătorii.
Prin analiza spectroscopică, cercetătorii au stabilit că injectarea de electroni a schimbat dispunerea atomilor de ditelluri de molibden de la o formă hexagonală la una care este monoclinică, care are mai mult o formă cuboidă înclinată. Odată ce electronii au fost retrași, structura cristalină a revenit la modelul său hexagonal original, arătând că tranziția de fază este reversibilă. Mai mult decât atât, aceste două tipuri de aranjamente atomice au simetrii foarte diferite, oferind un contrast mare pentru aplicațiile componentelor optice.
„Un astfel de dispozitiv subțire atomică ar putea avea funcții duale, care ar servi simultan ca tranzistori optici sau electrici și, prin urmare, vor lărgi funcționalitățile electronicii folosite în viața noastră de zi cu zi”, a spus Wang.
Sursă: Laboratorul Berkeley

Stratul de electrozi preparat din carbon activ (din frunze de ceai) îmbunătățește performanța celulelor de combustibil cu 33%(Electrode layer prepared from activated carbon (from tea leaves) enhances fuel cell performance by 33%)

Celulele de combustibil sunt considerate tehnologii energetice promițătoare ale viitorului, deoarece ele ajută la producerea de energie durabilă prin utilizarea de hidrocarburi ca și combustibili, cum ar fi metanolul, etanolul, acetona etc. prin mecanismul simplu de reacție de reducere a oxidării. Prin urmare, găsesc utilizarea lor în încărcătoare laptop, aplicații militare, în cazul în care accesul la energie electrică este dificil.Acest cadru utilizat în combinație cu negrul de fum convențional din stratul de difuzie a gazului catodic, a demonstrat că îmbunătățește performanța celulelor de combustibil cu 33% în condițiile de funcționare a celulelor de combustie cu metanol.

Posted: Oct 03, 2017

Electrode layer prepared from activated carbon (from tea leaves) enhances fuel cell performance by 33%
(Nanowerk Spotlight) Fuel cells are considered as promising energy technology of the future, as they aid in production of sustainable energy using hydrocarbons as fuels, such as methanol, ethanol, acetone etc by simple oxidation-reduction reaction mechanism. Hence find their use in laptop chargers, military applications, where the access to electricity is difficult.
However the wider spectrum of commercial perspective of methanol systems is greatly hindered by the mass transport phenomenon occurring in the electrode area of a fuel cell.
In a fuel cell, methanol undergoes oxidation on anode side, liberating protons and electrons. Electrons travel through external circuit and protons travel through membrane and reach the cathode side. On the cathode side, air undergoes reduction on cathode side, utilizing electrons and protons from anode reaction to form water.
This water, where the rate of formation is high at high current density regions covers the catalyst sites and prevents the incoming the air stream from further accession. This phenomenon – called ‘flooding’ – limits the operation of fuel cells at high current density regions. This is mitigated by optimising pore characteristics of carbon materials used in the gas diffusion layer of membrane electrode assembly (MEA) of a fuel cell.
MEA of a fuel cell consists of gas diffusion layer, catalyst layer and the membrane, all sandwiched together, with each layer playing a prominent role. The gas diffusion layer aids in effective reactant transport, catalyst layer in oxidation/reduction reaction and the membrane layer in transport of protons from anode to the cathode.
Schematic illustration of impact of using activated carbon (AC) in the gas diffusion layer comparable to standard (STD) MEA
Figure 1: Schematic illustration of impact of using activated carbon (AC) in the gas diffusion layer comparable to standard (STD) MEA. (Image: University of Manchester)
The mass transport limitation is addressed by working on the pore structure of carbon materials. Several carbon blacks: Vulcan XC-72, Ketjen Black, Acetylene Black Asbury 850, Denka Black and Mogul L are used widely. In addition to the performance limitation, the precursor for these carbon materials comes from the treatment of hydrocarbons at high temperature and pressure conditions.
In this work, reported in Electrochimica Acta („Enhanced performance based on a hybrid cathode backing layer using a biomass derived activated carbon framework for methanol fuel cells”), Manchester University chemical engineering researchers Prabhuraj Balakrishnan and Stuart M. Holmes prepared an activated carbon framework from tea leaves, obtained from the Black sea region of Tukey (from Ankara University) collaborators.
This framework used in combination with conventional carbon black in the cathode gas diffusion layer, has shown to improve the fuel cell performance by 33% in methanol fuel cell operating conditions.
More specifically, the cell performance underwent drastic changes in the mass transport region of the fuel cell polarization curve (Figure 1), comparable to the standard MEA. This is attributed to the pore structure (75.69% of mesopores and 24.31% of micropores) of this framework aiding in enhanced water removal, as a result more air molecules react with the platinum catalyst sites finally improving the fuel cell performance.
On increasing the composition of this activated carbon framework in the gas diffusion layer, the performance declined due to the poor electrical conductivity of the carbon. This shows that if the electrical conductivity of this activated carbon framework could be improved, this would decrease the reliance on conventional carbon blacks which currently suffers from source material (hydrocarbon) availability in addition to improving performance.
Provided by The University of Manchester as a Nanowerk exclusive

Catedralele Europei primesc o nouă viață datorită nanoparticulelor(Europe’s cathedrals get new life thanks to nanoparticles)

un material nou fabricat din nanoparticule inovatoare. Scopul este de a consolida structura interioară a pietrelor. Se aplică în principal pe marmură.Materialul dezvoltat de echipa de cercetare europeană ( proiectul Nano-Cathedral include carbonatul de calciu, care este un amestec de oxid de calciu, apă și dioxid de carbon.

Posted: Sep 26, 2017

Europe’s cathedrals get new life thanks to nanoparticles

(Nanowerk News) Just a few meters from Pisa’s famous Leaning Tower, restorers are defying scorching temperatures to bring back shine to the city’s Cathedral.
Ordinary restoration techniques like laser are being used on much of the stonework that dates back to the 11th century. But a brand new technique is also being used: a new material made of innovative nanoparticles. The aim is to consolidate the inner structure of the stones. It’s being applied mainly on marble.
Pisa cathedral
Pisa cathedral
“Marble has very low porosity, which means we have to use nanoparticles in order to go deep inside the stone, to ensure that the treatment is both efficient while still allowing the stone to breathe,” explains Roberto Cela, civil engineer at Opera Della Primaziale Pisana.
The material developed by the European research team (Nano-Cathedral project includes calcium carbonate, which is a mix of calcium oxide, water and carbon dioxide.
The nanoparticles penetrate the stone cementing its decaying structure.
“It is important that these particles have the same chemical nature as the stones that are being treated, so that the physical and mechanical processes that occur over time don’t lead to the break-up of the stones,” says Dario Paolucci, chemist at the University of Pisa.
Vienna’s St Stephen’s is another of the five cathedrals where the new restoration materials are being tested.
The first challenge for researchers is to determine the mechanical characteristics of the cathedral’s stones. Since there are few original samples to work on, they had to figure out a way of “ageing” samples of stones of similar nature to those originally used.
“We tried different things: we tried freeze storage, we tried salts and acids, and we decided to go for thermal ageing,” explains Matea Ban, material scientist at the University of Technology in Vienna. “So what happens is that we heat the stone at certain temperatures. Minerals inside then expand in certain directions, and when they expand they build up stresses to neighbouring minerals and then they crack, and we need those cracks in order to consolidate them.”
Consolidating materials were then applied on a variety of limestones, sandstones and marble – a selection of the different types of stones that were used to build cathedrals around Europe.
What researchers are looking for are very specific properties.
“First of all, the consolidating material has to be well absorbed by the stone,” says petrologist Johannes Weber of the University of Applied Arts in Vienna. “Then, as it evaporates, it has to settle properly within the stone structure. It should not shrink too much. All materials shrink when drying, including consolidating materials. They should adhere to the particles of the stone but shouldn’t completely obstruct its pores.”
Further tests are underway in cathedrals across Europe in the hope of better protecting our invaluable cultural heritage.
Source: European Commission

Patru elemente fac platforma optică 2-D(Four elements make 2-D optical platform)

au descoperit un aliaj bidimensional cu o bandgap optica care poate fi reglat de temperatura folosita pentru ao creste.A dezvoltat aliajul de patru componente din metale tranziționale, molibden și tungsten, cu sulfuri de calciu și seleniu într-un cuptor de depunere chimică de vapori. Ei au descoperit că schimbările de temperatură au făcut modificări subtile în modul în care atomii au asamblat și, de asemenea, au modificat proprietățile care determină modul în care absorb și emit lumină.

Posted: Sep 21, 2017

Four elements make 2-D optical platform

(Nanowerk News) Rice University scientists have discovered a two-dimensional alloy with an optical bandgap that can be tuned by the temperature used to grow it.
The Rice lab of materials scientist Pulickel Ajayan grew the four-component alloy of transition metals molybdenum and tungsten with chalcogens sulfur and selenium in a chemical vapor deposition furnace. They found changes in temperature made subtle changes in the way atoms assembled and also altered the properties that determine how they absorb and emit light.
Subtle changes in growth temperature alters the form of a four-component alloy
Subtle changes in growth temperature alters the form of a four-component alloy created at Rice University. The alloy can be tuned to alter its optical bandgap, which may be of use in the design of solar cells and light-emitting diodes. (Illustration by Alex Kutana)
Their experiments were built upon work by the lab of Rice theoretical physicist Boris Yakobson, which created scores of models to predict how various combinations of the four elements should work.
The process should be of interest to engineers looking to make smaller, more-efficient devices. Because the bandgap falls in the optical range of the electromagnetic spectrum, the researchers said solar cells and light-emitting diodes might be the first beneficiaries.
The paper appears as a cover story in the current issue of Advanced Materials („Quaternary 2D Transition Metal Dichalcogenides (TMDs) with Tunable Bandgap”).
The team led by co-lead author and Rice research scientist Alex Kutana generated 152 random models of the material that showed the bandgap could be tuned from 1.62 to 1.84 electron volts by varying the growth temperature from 650 and 800 degrees Celsius (1,202 to 1,472 degrees Fahrenheit).
The experimental team led by Sandhya Susarla then made and tested the thermodynamically stable materials in a furnace at 50-degree increments. Scientists at Oak Ridge National Laboratory led by postdoctoral researcher Jordan Hachtel produced microscope images that identified and detailed the position of each atom in the materials.
“Labs have made 2-D materials with two or three components, but we don’t believe anyone has tried four,” said co-author and Rice postdoctoral researcher Chandra Sekhar Tiwary. “Having four components gives us an additional degree of freedom. With fewer materials, every adjustment you make to change the bandgap turns it into a different material. That’s not the case here.”
“What we’ve made should be very useful,” added Susarla, a Rice graduate student. “For applications like solar cells and LEDs, you need a material that has a broad bandgap.”
Tiwary said the material can be tuned to cover the entire spectrum of visible light, from 400- to 700-nanometer wavelengths. “That’s a huge range we can cover by just changing this composition,” he said. “If we choose the composition correctly, we can hit the correct bandgap or correct emission point.”
“These materials are arguably the most important 2-D semiconductors because of their excellent optoelectronic properties and low cost,” Kutana said. “Our high-throughput calculations permitted us to avoid prior assumptions about how the alloy bandgap behaved. The surprising outcome was how regular the bandgap changes were, resulting in optical properties that are both useful and predictable.”
Source: By Mike Williams, Rice University