Cristalele care pot fi transformate pot permite noi cipuri de memorie(Switchable crystals could enable new memory chips)

au dezvoltat un material subțire, a cărui fază și proprietăți electrice pot fi schimbate între metale și semiconductoare pur și simplu prin aplicarea unei mici tensiuni. Materialul rămâne apoi în noul său configurație, până când este deconectat de o altă tensiune. el deschide calea pentru aplicarea acestor materiale atat in dispozitive electrochimice in stare solida pentru conversia eficienta a stocarii de energie sau oxigen, cat si in aplicatii posibile intr-un nou tip de dispozitive de memorie „.

Posted: Jan 20, 2016

Switchable crystals could enable new memory chips

(Nanowerk News) Two MIT researchers have developed a thin-film material whose phase and electrical properties can be switched between metallic and semiconducting simply by applying a small voltage. The material then stays in its new configuration until switched back by another voltage. The discovery could pave the way for a new kind of “nonvolatile” computer memory chip that retains information when the power is switched off, and for energy conversion and catalytic applications.
The findings, reported in the journal Nano Letters in a paper („Voltage-Controlled Topotactic Phase Transition in Thin-Film SrCoOx Monitored by In Situ X-ray Diffraction”) by MIT materials science graduate student Qiyang Lu and associate professor Bilge Yildiz, involve a thin-film material called a strontium cobaltite, or SrCoOx.
This diagram shows how an electrical voltage can be used to modify the oxygen concentration, and therefore the phase and structure, of strontium cobaltites
This diagram shows how an electrical voltage can be used to modify the oxygen concentration, and therefore the phase and structure, of strontium cobaltites. Pumping oxygen in and out transforms the material from the brownmillerite form (left) to the perovskite form (right). (Courtesy of the researchers)
Usually, Yildiz says, the structural phase of a material is controlled by its composition, temperature, and pressure. “Here for the first time,” she says, “we demonstrate that electrical bias can induce a phase transition in the material. And in fact we achieved this by changing the oxygen content in SrCoOx.”
“It has two different structures that depend on how many oxygen atoms per unit cell it contains, and these two structures have quite different properties,” Lu explains.
One of these configurations of the molecular structure is called perovskite, and the other is called brownmillerite. When more oxygen is present, it forms the tightly-enclosed, cage-like crystal structure of perovskite, whereas a lower concentration of oxygen produces the more open structure of brownmillerite.
The two forms have very different chemical, electrical, magnetic, and physical properties, and Lu and Yildiz found that the material can be flipped between the two forms with the application of a very tiny amount of voltage — just 30 millivolts (0.03 volts). And, once changed, the new configuration remains stable until it is flipped back by a second application of voltage.
Strontium cobaltites are just one example of a class of materials known as transition metal oxides, which is considered promising for a variety of applications including electrodes in fuel cells, membranes that allow oxygen to pass through for gas separation, and electronic devices such as memristors — a form of nonvolatile, ultrafast, and energy-efficient memory device. The ability to trigger such a phase change through the use of just a tiny voltage could open up many uses for these materials, the researchers say.
Previous work with strontium cobaltites relied on changes in the oxygen concentration in the surrounding gas atmosphere to control which of the two forms the material would take, but that is inherently a much slower and more difficult process to control, Lu says. “So our idea was, don’t change the atmosphere, just apply a voltage.”
“Voltage modifies the effective oxygen pressure that the material faces,” Yildiz adds. To make that possible, the researchers deposited a very thin film of the material (the brownmillerite phase) onto a substrate, for which they used yttrium-stabilized zirconia.
In that setup, applying a voltage drives oxygen atoms into the material. Applying the opposite voltage has the reverse effect. To observe and demonstrate that the material did indeed go through this phase transition when the voltage was applied, the team used a technique called in-situ X-ray diffraction at MIT’s Center for Materials Science and Engineering.
The basic principle of switching this material between the two phases by altering the gas pressure and temperature in the environment was developed within the last year by scientists at Oak Ridge National Laboratory. “While interesting, this is not a practical means for controlling device properties in use,” says Yildiz. With their current work, the MIT researchers have enabled the control of the phase and electrical properties of this class of materials in a practical way, by applying an electrical charge.
In addition to memory devices, the material could ultimately find applications in fuel cells and electrodes for lithium ion batteries, Lu says.
“Our work has fundamental contributions by introducing electrical bias as a way to control the phase of an active material, and by laying the basic scientific groundwork for such novel energy and information processing devices,” Yildiz adds.
In ongoing research, the team is working to better understand the electronic properties of the material in its different structures, and to extend this approach to other oxides of interest for memory and energy applications, in collaboration with MIT professor Harry Tuller.
José Santiso, the nanomaterials growth division leader at the Catalan Institute of Nanoscience and Nanotechnology in Barcelona, Spain, who was not involved in this research, calls it “a very significant contribution” to the study of this interesting class of materials, and says “it paves the way for the application of these materials both in solid state electrochemical devices for the efficient conversion of energy or oxygen storage, as well as in possible applications in a new kind of memory devices.”
Source: By David L. Chandler, MIT

Amortizoarele de ultraviolete pe bază de sticlă acționează ca „scuturi biologice”(Glass-based ultraviolet absorbers act as ‘biological shields’)

un grup de cercetători din China a dezvoltat o nouă metodă de a crea materiale transparente, pe bază de sticlă, cu putere de absorbție UV și durate lungi de viață. Echipa a demonstrat că noul sticlă protejează efectiv celulele vii și coloranții organici și crede că ar putea fi dezvoltat și ca un scut transparent pentru protejarea electronicii în spațiu. Ele descriu rezultatele lor în Materialul optic Express ( „Compozit de sticlă ca absorbant UV robust pentru protecție biologică” ).Cercetatorii au folosit un oxid de metal – oxid de ceriu (IV) (CeO 2 ) – bine cunoscut pentru abilitatea sa de a absorbi fotonii UV pentru a ambarca absorbantul UV compozit pe baza de sticla.
Alte caracteristici cheie ale materialului compozit final sunt transparența optică a sticlei și capacitatea materialului de a suprima separarea electronilor generați fotografic și a găurilor. Caracteristica ulterioară încetinește o reacție indusă de lumină care ar conduce la defalcarea ulterioară a materialului sub expunere prelungită la radiațiile UV.

Posted: Jan 20, 2016

Glass-based ultraviolet absorbers act as ‘biological shields’

(Nanowerk News) If you’ve ever experienced a bad sunburn, you know the damage that ultraviolet (UV) light can cause to living cells (like your skin). Out in space, where the level of radiation from the sun can be even higher, it can damage sensitive electronics aboard in-flight spacecraft.
The dangers of UV light have prompted scientists to search for versatile materials that block UV and can withstand long radiation exposure times without falling apart. Now a group of researchers in China has developed a new method to create transparent, glass-based materials with UV-absorbing power and long lifetimes. The team demonstrated that the new glass effectively protects living cells and organic dyes, and believe it could also be developed as a transparent shield to protect electronics in space. They describe their results in Optical Materials Express („Glass composite as robust UV absorber for biological protection”).
UV-Induced Changes to Giant Cells
These images show UV-induced morphological changes of multinucleated giant cells, unprotected and protected by the group’s UV absorber. (Image: Shifeng Zhou/ South China University of Technology)
The researchers used a metal oxide –cerium (IV) oxide (CeO2) – well-known for its ability to absorb UV photons to craft the composite glass-based UV absorber.
Other key features of the final composite material are the optical transparency of the glass and the material’s ability to suppress the separation of photo-generated electrons and holes. The later feature slows down a light-induced reaction that would lead to the ultimate breakdown of the material under prolonged exposure to UV radiation.
The method the team developed is based on the self-limited nanocrystallization of glass.
„Self-limited nanocrystallization of glass can be achieved by taking advantage of the rigid environment of the solid-state matrix, rather than the conventional solution and vapor conditions to modulate the ionic migration kinetics,” explained Shifeng Zhou, School of Materials Science and Engineering, South China University of Technology, Guangzhou, China. „It allows us to create glass-ceramics embedded with a CeO2:fluorine (F) nanostructure.”
The viscous glass matrix involved poses a considerable constraint for oxide (O2-) and F– ion diffusion, so the group gradually etches trifluorocerium (CeF3) by O2- ions within an oxide matrix until F–doped CeO2 is generated in a controllable manner. It’s important to note that this technology is also routinely used to prepare other UV absorbers such as zinc oxide (ZnO) and titanium oxide (TiO2).
„This work establishes an effective approach for the functionalization of glass,” said Zhou. „And it allowed us to demonstrate the construction of a novel glass-based UV absorber.”
The group’s innovative approach for fabricating the UV absorber has important implications „for the construction of novel glass materials with new functions via microstructure engineering,” he added.
Among the group’s key discoveries was finding that the self-limited nanocrystallinization of glass is indeed an effective way to functionalize it. The special glass they created suppresses photocatalytic and catalytic activity, while boasting an extremely high UV-absorbing capacity.
„Our glass shows excellent optical quality, and it can be easily fabricated either in bulk form or as a film,” said Zhou. „It effectively protects organic dye and living cells from UV radiation damage.”
Potential applications for the group’s work include radiation hardening of electronic devices, serving as a biological shield, and preserving cultural artifacts and relics.
„In space, the high-energy radiation environment encountered by electronic equipment aboard spacecraft can be quite damaging,” noted Zhou. „Fortunately, in the future, if you add a radiation-blocking coating onto the surface of the package – a transparent glass/polymer material – the device would be well protected, and its service lifetime may be prolonged.”
In terms of applications as biological shields and to preserve cultural artifacts and relics, the special glass can „protect cells from UV-induced damage,” he added.
Going forward, the group plans to focus their efforts on developing other novel and effective glass-based UV absorbers, using the self-limited nanocrystallization method.
„We’ll explore ways for large-scale fabrication of this type of film, which is extremely important for practical applications,” said Zhou. „Our group will also further study the functionalization of glass based on its microstructure engineering, because we believe this fundamental research may have great significance for the glass industry.”
Source: The Optical Society

Electrolitul celulelor de combustie dezvoltat pentru a oferi o energie mai curată și mai eficientă(Fuel cell electrolyte developed to offer cleaner, more efficient energy)

Un nou material electrolit subțire, care ajută celulele de combustie cu oxizi solizi să funcționeze mai eficient și mai ieftin decât cele compuse din materiale convenționale și care are aplicații potențiale pentru sursele de energie portabile, a fost dezvoltat la Universitatea din Cambridge.
Aceste materiale noi oferă posibilitatea fie de a îmbunătăți în mod semnificativ eficiența sistemelor actuale de celule de combustibil la temperaturi ridicate, fie de a atinge aceleași niveluri de performanță la temperaturi mult mai scăzute. Oricare dintre aceste abordări ar putea permite consumul de combustibil și consumul de deșeuri mult mai redus.

Posted: Jan 20, 2016

Fuel cell electrolyte developed to offer cleaner, more efficient energy

(Nanowerk News) A new thin-film electrolyte material that helps solid oxide fuel cells operate more efficiently and cheaply than those composed of conventional materials, and has potential applications for portable power sources, has been developed at the University of Cambridge.
These new materials offer the possibility of either significantly improving the efficiency of current high-temperature fuel cell systems, or achieving the same performance levels at much lower temperatures. Either of these approaches could enable much lower fuel consumption and waste energy. The material was co-invented by Professor Judith Driscoll of the Department of Materials Science and Metallurgy and her colleague Dr Shinbuhm Lee, with support from collaborators at Imperial College and at three different labs in the US.
Solid oxide fuel cells are comprised of a negative electrode (cathode) and positive electrode (anode), with an electrolyte material sandwiched between them. The electrolyte transports oxygen ions from the cathode to the anode, generating an electric charge. Compared to conventional batteries, fuel cells have the potential to run indefinitely, if supplied by a source of fuel such as hydrogen or a hydrocarbon, and a source of oxygen.
By using thin-film electrolyte layers, micro solid oxide fuel cells offer a concentrated energy source, with potential applications in portable power sources for electronic consumer or medical devices, or those that need uninterruptable power supplies such as those used by the military or in recreational vehicles.
“With low power requirements and low levels of polluting emissions, these fuel cells offer an environmentally attractive solution for many power source applications,” said Dr Charlanne Ward of Cambridge Enterprise, the University’s commercialisation arm, which is managing the patent that was filed in the US. “This opportunity has the potential to revolutionise the power supply problem of portable electronics, by improving both the energy available from the power source and safety, compared with today’s battery solutions.”
In addition to providing significantly improved conductivity, the new electrolyte material offers:
  • minimal heat loss and short circuiting due to low electronic conductivity
  • minimal cracking under heat cycling stress due to small feature size in the construction
  • high density, reducing the risk of fuel leaks
  • simple fabrication using standard epitaxial growth and self-assembly techniques
“The ability to precisely engineer and tune highly crystalline materials at the nanoscale is absolutely key for next-generation power generation and storage of many different kinds,” said Driscoll. “Our new methods and understanding have allowed us to exploit the very special properties of nanomaterials in a practical and stable thin-film configuration, resulting in a much improved oxygen ion conducting material.”
In October, a paper on the enhancement of oxygen ion conductivity in oxides was published in Nature Communications („Strongly enhanced oxygen ion transport through samarium-doped CeO2 nanopillars in nanocomposite films”). It is this enhancement that improves efficiency and enables low-temperature operation of fuel cells. As a result of the reported advantages, the novel electrolyte material can also potentially be used in the fabrication of improved electrochemical gas sensors and oxygen separation membranes (to extract oxygen molecules from the air). The inventors have also published two other papers showing the enhanced ionic conduction in different materials systems, one in Nano Letters („Ionic Conductivity Increased by Two Orders of Magnitude in Micrometer-Thick Vertical Yttria-Stabilized ZrO2 Nanocomposite Films”) and one in Advanced Functional Materials („Strain Tuning and Strong Enhancement of Ionic Conductivity in SrZrO3–RE2O3 (RE = Sm, Eu, Gd, Dy, and Er) Nanocomposite Films”).
Source: University of Cambridge

Detectarea moleculei unice a contaminanților, a explozivilor sau a bolilor acum posibile(Single molecule detection of contaminants, explosives or diseases now possible)

detecția moleculei unice a contaminanților, a explozivilor sau a bolilor acum posibile; O tehnică care combină ultrasensibilitatea împrăștierii Raman îmbunătățită la suprafață cu un surfing alunecos inventat de cercetătorii

36 sept

Cum îi ajută pe scoici (How seashells get their strength)

Deși toate cele trei sunt fabricate din cristale de carbonat de calciu, materialele dure includ grupuri de materie biologică moale, care fac mult mai puternice.Compuși mai buni prin chimie
Pasii captează micelii din motive chimice, nu mecanice, iar comprimarea rezultată a micelilor de către pași duce apoi la forțe care explică unde vine rezistența

33 sept