Lună: ianuarie 2016

Simțiți spații cu „pălăria de proximitate”(Feeling spaces with the „proximity hat” )

Senzorul ultrasonic, bateriile și tampoanele de presiune sunt părți ale noului sistem care poate fi pus pe cap ca o pălărie sau bandă de susținere

101 sept

Polar vortex observate în feroelectrice

Materialele feroase prezintă proprietăți electrice sau magnetice unice – sau ambele în cazul multiferroizelor. De exemplu, câmpul electric al unui material feroelectric poate fi polarizat în favoarea unei încărcări pozitive sau negative cu aplicarea unui câmp electric extern. Într-un material feromagnetic, aplicarea unui câmp magnetic extern aliniază rotația particulelor încărcate, rezultând materialul devenind un magnet permanent. În ultimii ani, sa descoperit că aplicarea unui câmp magnetic extern poate produce, de asemenea, cicloane cu dimensiuni atomice de cercuri, care acționează ca particule de baryon și pot fi deplasate coerent pe distanțe macroscopice. Aceste proprietăți fac Skyrmions candidați excelenți pentru aplicații spintronice.

Posted: Jan 29, 2016

Polar vortices observed in ferroelectric

(Nanowerk News) The observation in a ferroelectric material of „polar vortices” that appear to be the electrical cousins of magnetic skyrmions holds intriguing possibilities for advanced electronic devices. These polar vortices, which were theoretically predicted more than a decade ago, could also „rewrite our basic understanding of ferroelectrics” according to the researchers who observed them.
A team of scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have recorded the first ever observations of rotating topologies of electrical polarization that are similar to the discrete swirls of magnetism known as „skyrmions.” If these smoothly rotating vortex/anti-vortex topologies prove to be electrical skyrmions, they could find potential applications in ultracompact data storage and processing, and could also lead to the production of new states of matter and associated phenomena in ferroic materials.
polar vortices in a ferroelectic material
The first ever observations of polar vortices in a ferroelectic material could find potential applications in ultracompact data storage and processing and the production of new states of matter.
„It has long been thought that rotating topological structures are confined to magnetic systems and aren’t possible in ferroelectric materials, but through the creation of artificial superlattices, we have controlled the various energies of a ferrolectric material to promote competition that lead to such new states of matter and polarization arrangements,” says Ramamoorthy Ramesh, Berkeley Lab’s Associate Laboratory Director for Energy Technologies and the co-principal investigator for this study. He also holds UC Berkeley’s Purnendu Chatterjee Endowed Chair in Energy Technologies.
„Ferroelectric materials such as the materials used in this work have produced a number of exciting emergent properties over the years, but these smoothly-rotating polar vortex structures really are different,” says Lane Martin, a faculty scientist with Berkeley Lab’s Materials Sciences Division and Associate Professor in UC Berkeley’s Department of Materials Science and Engineering, who is this study’s co-principal investigator. „I think if you surveyed the community many would shake their heads in disbelief at such structures, but it turns out there really is a tendency for vortex states to form in nature even in these polar systems. And, when one looks more broadly, vortex structures can occur across huge length scales – from galaxies and weather systems all the way down to 10s of atoms as in our case.”
Ramesh and Martin are the corresponding authors of a Nature paper describing this study in detail („Observation of polar vortices in oxide superlattices”).
Ferroic materials display unique electrical or magnetic properties – or both in the case of multiferroics. For example, the electrical field of a ferroelectric material can be polarized in favor of either a positive or negative charge with the application of an external electrical field. In a ferromagnetic material, the application of an external magnetic field aligns the spin of their charged particles, resulting in the material becoming a permanent magnet. In recent years, it was discovered that the application of an external magnetic field can also produce atom-sized cyclones of skyrmions, which act like baryon particles and can be moved coherently over macroscopic distances. These properties make skyrmions excellent candidates for spintronic applications.
Vortex structures occur in nature across a broad range of length scales
Vortex structures occur in nature across a broad range of length scales, from galaxies and weather systems all the way down to the atomic scale of polar vortices in ferroics.
„We believe the polar vortices we observed in ferroelectrics, when fully explored, have the potential to be topological states of matter that are similar to magnetic skyrmions,” Ramesh says. „The fact that our polar vortices can display emergent behavior in their electronic, optical, magnetic and other properties suggests that heretofore unexplored applications and functionalities could be possible.”
Ramesh, Martin and their collaborators worked with what has become a canonical system in the community, ultrafine layered structures built from lead titanate and strontium titante compounds controlled down to a few unit cells each, in which each unit cell is approximately 0.4 nanometers thick. They created superlattices that harbored a three-way competition between elastic, electrostatic and gradient energies within the layers of lead titanate and strontium titanate. This unique three-way competition gives rise to the polar vortices.
„As we tune the period lengths of our superlattices, we can tune the relative importance of these three energy scales,” Martin says. „Although rather exotic things can occur if one changes the superlattice period to be both smaller and bigger than we studied here, we really found the ‘sweet-spot’ in this work that produced these polar vortices which are an entirely new phenomenon.”
A combination of scanning transmission electron microscopy (STEM) and X-ray diffraction studies were used observe and characterize the polar vortices. The STEM work was carried out at Berkeley Lab’s Molecular Foundry, a DOE Office of Science User Facility, on TEAM 0.5, the world’s most powerful transmission electron microscope. The X-ray diffraction work was carried out at the Advanced Photon Source, another DOE Office of Science User Facility, which is hosted by DOE’s Argonne National Laboratory.
„Our study is really indicative of how DOE-funded research programs can bring together a diverse range of expertise, including atomically-controlled materials synthesis and cutting-edge research facilities, and materials theory to enable foundational discoveries that really change the way we think about exotic materials and the possibilities for using them,” says Ramesh.
„This is just the beginning for the study of polar vortices in ferroelectric materials,” Martin says. „We’re observing a new state of matter and we have our work cut out for us in mapping and understanding how it evolves. We can imagine adding a magnetic spin component to similar superlattices and thus potentially paving a pathway to fundamentally demonstrate electric-field control of magnetism.”
Source: By Lynn Yarris, Lawrence Berkeley National Laboratory
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Read more: Polar vortices observed in ferroelectric

Tehnica de creștere nanosheet ar putea revoluționa producția de nanomateriale

Datorită proprietăților chimice, agentul tensioactiv se asamblează într-un singur strat la suprafața lichidului, cu ioni sulfați încărcați negativ în direcția lichidului. Acești ioni sulfați extrag ionii de zinc încărcați pozitiv din interiorul lichidului la suprafață și în decurs de câteva ore sugerează suficient ioni de zinc pentru a forma nanopreți de oxid de zinc continuu doar câteva straturi atomice groase.

Posted: Jan 29, 2016

Nanosheet growth technique could revolutionize nanomaterial production

(Nanowerk News) After six years of painstaking effort, a group of University of Wisconsin-Madison materials scientists believe the tiny sheets of the semiconductor zinc oxide they’re growing could have huge implications for the future of a host of electronic and biomedical devices.
The group – led by Xudong Wang, a UW-Madison professor of materials science and engineering, and postdoctoral researcher Fei Wang – has developed a technique for creating nearly two-dimensional sheets of compounds that do not naturally form such thin materials. It is the first time such a technique has been successful.
The researchers described their findings in the journal Nature Communications („Nanometre-thick single-crystalline nanosheets grown at the water–air interface”).
nanosheet
The new nanoscale manufacturing process draws zinc to the surface of a liquid, where it forms sheets just a few atoms thick. (Image: Xudong Wang)
Essentially the microscopic equivalent of a single sheet of paper, a 2-D nanosheet is a material just a few atoms thick. Nanomaterials have unique electronic and chemical properties compared to identically composed materials at larger, conventional scales.
„What’s nice with a 2-D nanomaterial is that because it’s a sheet, it’s much easier for us to manipulate compared to other types of nanomaterials,” says Xudong Wang.
Until now, materials scientists were limited to working with naturally occurring 2-D nanosheets. These natural 2-D structures include graphene, a single layer of graphite, and a limited number of other compounds.
Developing a reliable method to synthesize and manufacture 2-D nanosheets from other materials has been a goal of materials researchers and the nanotechnology industry for years.
In their technique, the UW-Madison team applied a specially formulated surfactant – a detergent-like substance – onto the surface of a liquid containing zinc ions.
Due to its chemical properties, the surfactant assembles itself into a single layer at the surface of the liquid, with negatively charged sulfate ions pointed in the direction of the liquid. Those sulfate ions draw the positively charged zinc ions from within the liquid to the surface, and within a couple hours enough zinc ions are drawn up to form continuous zinc oxide nanosheets only a few atomic layers thick.
Xudong Wang first had the idea for using a surfactant to grow nanosheets during a lecture he was giving in a course on nanotechnology in 2009.
„The course includes a lecture about self-assembly of monolayers,” he says. „Under the correct conditions, a surfactant will self-assemble to form a monolayer. This is a well-known process that I teach in class. So while teaching this, I wondered why we wouldn’t be able to reverse this method and use the surfactant monolayer first to grow the crystalline face.”
After five years of trial and error with different surfactant solutions, the idea paid off.
„We are very excited about this,” says Xudong Wang. „This is definitely a new way to fabricate 2-D nanosheets, and it has great potential for different materials and for many different applications.”
Already, the researchers have found that the 2-D zinc oxide nanosheets they’ve grown are able to function as semiconductor transistors called a p-type, the opposite electronic behavior of naturally occurring zinc oxide. Researchers have for some time attempted to produce zinc oxide with reliable p-type semiconductor properties.
Zinc oxide is a very useful component of electronic materials, and the new nanosheets have potential for use in sensors, transducers and optical devices.
But the zinc oxide nanosheets are only the first of what could be a revolution in 2-D nanomaterials. Already, the UW-Madison team is applying its surfactant method to growing 2-D nanosheets of gold and palladium, and the technique holds promise for growing nanosheets from all sorts of metals that wouldn’t form them naturally.
„It brings a lot of new functional material to this 2-D material category,” Wang says.
Source: University of Wisconsin-Madison

Read more: Nanosheet growth technique could revolutionize nanomaterial production

Patriot Ordnance Factory POF-SUA P-300 (de asemenea scris P300). 300 Win.Mag (300WM) Piston Tactic AR Rifle / Carbine debutează la SHOT Show 2016!(Patriot Ordonance Factory POF-USA P-300(also written P300). 300 Win.Mag(300WM)Tactical Piston AR Rifle/Carbine Debuts at SHOT Show 2016!)

Înțelegerea lui DR este că POF-SUA P-300 utilizează în prezent un polimer Nemo Arms 300WM și va veni cu unul dintre declanșatoarele excelente ale puilor POF, în funcție de preferințele utilizatorilor finali

99 sept

O alternativă la platină: compuși ai azotului de fier ca catalizatori în grafen(An alternative to platinum: iron-nitrogen compounds as catalysts in graphene)

au produs un material catalitic eficient din punct de vedere al costurilor pentru celulele de combustie folosind un nou proces de preparare pe care l-au analizat în detaliu. Se compune din complexe de fier-azot încorporate în insulele mici de grafen cu numai câțiva nanometri în diametru

Posted: Jan 27, 2016

An alternative to platinum: iron-nitrogen compounds as catalysts in graphene

(Nanowerk News) Teams at Helmholtz Zentrum Berlin (HZB) and TU Darmstadt have produced a cost-effective catalyst material for fuel cells using a new preparation process which they analysed in detail. It consists of iron-nitrogen complexes embedded in tiny islands of graphene only a few nanometres in diameter. It is only the FeN4 centres that provide the excellent catalytic efficiency – approaching that of platinum. The results are interesting for solar fuels research as well and have been published in the Journal of the American Chemical Society („On an easy way to prepare Metal-Nitrogen doped carbon with exclusive presence of MeN4-type sites active for the ORR”).
Nano-island of graphene in which iron-nitrogen complexes are embedded
Nano-island of graphene in which iron-nitrogen complexes are embedded. The FeN4 complexes (shown in orange) are catalytically active. (Image: S. Fiechter/HZB)
Fuel cells convert the chemical energy stored in hydrogen (H2) into electrical energy by electrochemically “combusting” hydrogen gas with oxygen (O2) from the air into water (H2O), thereby generating electricity. As a result, future electric automobiles might be operated quite well with fuel cells instead of with heavy batteries. But for “cold” combustion of hydrogen and oxygen to function well, the anode and cathode of the fuel cell must be coated with extremely active catalysts. The problem is that the platinum-based catalysts employed for this contribute about 25 per cent of the total fuel-cell costs.
However, iron-nitrogen complexes in graphene (known as Fe-N-C catalysts) have been achieving levels of activity comparable to Pt/C catalysts for several years already. “Systematic investigation of Fe-N-C catalysts was difficult though, since most approaches for preparing the materials lead to heterogeneous compounds. These contain various species of iron compounds such as iron carbides or nitrides besides the intended FeN4 centres”, explains Sebastian Fiechter of HZB.
High density of catalytically active centres
“We had already developed a new preparation method at HZB a few years ago to produce an inexpensive catalyst material from organometallic compounds such as iron or cobalt porphyrin”, reports Peter Bogdanoff, HZB. Ulrike Kramm and Iris Herrmann-Geppert improved the process for producing it as part of their doctoral studies at HZB. As a result, the metal-N-C catalysts developed at HZB held the world record for the highest density of catalytically active centres of various nitro-metallic compounds up to about 2011. However, it remained unclear as to which inorganic compounds influenced the catalytic efficiency. The team was now able to determine this.
Purification process removes interfering compounds
The highlight in the current work is a purification process (a combination of thermal treatment with a subsequent etching step) by which the proportion of metallic compounds that interfere with catalytic activity can be substantially reduced, even for catalysts that are highly heterogeneous. The interesting thing here is that the activity increases enormously! Ulrike Kramm, who has since become a junior professor at TU Darmstadt, was successful in purifying several catalysts to such an extent that all the iron present in the graphene layers was exclusively in form of complexes made of iron and four nitrogen atoms (FeN4). The scientists thereby disproved the hypothesis debated among experts by which improvement in the activity of the FeN4 centres only resulted from promoters, as they are known, such as iron nanoparticles.
Now verified: FeN4 centres provide the high catalytic efficiency even without promoters
“To check this hypothesis, we employed numerous complex measurement techniques like Mößbauer spectroscopy, electron paramagnetic resonance spectroscopy and X-ray absorption spectroscopy at BESSY II. These enabled us to precisely survey the atomic structure of the catalytic centres”, Ulrike Kramm reports.
“The purification process enables us now to create catalysts having exclusively FeN4 centres. This allows us to subsequently select compounds to be added afterwards as promoters that further improve the activity level or stability of these catalysts”, as Ulrike Kramm summarises her research approach at TU Darmstadt.
Sebastian Fiechter and Peter Bogdanoff are continuing their research at HZB on novel catalysts, especially in regard to hydrogen generation using sunlight. “We can also use the insights into how these metal-N-C catalysts work in our on-going development of catalysing materials for solar-based hydrogen production at HZB,” says Fiechter.
Together, the research activities at HZB and TU Darmstadt could enable the development of a complete regenerative energy cycle, using solar hydrogen in low cost fuel cells, thus producing electricity without climate gas emission.
Source: Helmholtz Zentrum Berlin

Simplificarea celulelor solare cu un amestec nou de materiale(Simplifying solar cells with a new mix of materials)

O echipă internațională de cercetare a simplificat pașii de creare a celulelor solare de înaltă eficiență prin aplicarea unui nou amestec de materiale într-un design standard. Structurile de celule solare sunt utilizate în panouri solare pentru a transforma lumina solară în energie electrică.
Amestecul special de materiale – care ar putea fi de asemenea util în componentele semiconductoare – elimină necesitatea unui proces cunoscut sub numele de dopaj care să conducă proprietățile dispozitivului prin introducerea de atomi străini în contactele sale electrice. Acest proces de dopaj adaugă complexitate dispozitivului și îi poate degrada performanțele

Posted: Jan 27, 2016

Simplifying solar cells with a new mix of materials

(Nanowerk News) An international research team has simplified the steps to create highly efficient silicon solar cells by applying a new mix of materials to a standard design. Arrays of solar cells are used in solar panels to convert sunlight to electricity.
The special blend of materials–which could also prove useful in semiconductor components–eliminates the need for a process known as doping that steers the device’s properties by introducing foreign atoms to its electrical contacts. This doping process adds complexity to the device and can degrade its performance.
„The solar cell industry is driven by the need to reduce costs and increase performance,” said James Bullock, the lead author of the study, published this week in Nature Energy („Efficient silicon solar cells with dopant-free asymmetric heterocontacts”). Bullock participated in the study as a visiting researcher at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.
The Making of a Solar Cell
In this illustration, the top images show a cross-section of a solar cell design, called DASH, that uses a combination of moly oxide and lithium fluoride. This combination of materials allows the device to achieve high efficiency in converting sunlight to energy without the need for a process known as doping. The bottom images shows the dimensions of the DASH solar cell components. (© Nature Publishing Group)
„If you look at the architecture of the solar cell we made, it is very simple,” said Bullock, of Australian National University (ANU). „That simplicity can translate to reduced cost.”
Other scientists from Berkeley Lab, UC Berkeley, ANU and The Swiss Federal Institute of Technology of Lausanne (EPFL) also participated in the study.
Bullock added, „Conventional silicon solar cells use a process called impurity doping, which does bring about a number of limitations that are making further progress increasingly difficult.”
Most of today’s solar cells use crystalline silicon wafers. The wafer itself, and sometimes the layers deposited on the wafer, are doped with atoms that either have electrons to spare when they bond with silicon atoms, or alternatively generate electron deficiencies, or „holes.” In both cases, this doping enhances electrical conductivity.
In these devices, two types of dopant atoms are required at the solar cell’s electrical contacts to regulate how the electrons and holes travel in a solar cell so that sunlight is efficiently converted to electrical current that flows out of the cell.
Crystalline silicon-based solar cells with doped contacts can exceed 20 percent efficiency–meaning more than 20 percent of the sun’s energy is converted to electricity. A dopant-free silicon cell had not previously exceeded 14 percent efficiency.
The new study, though, demonstrated a dopant-free silicon cell, referred to as a DASH cell (dopant free asymmetric heterocontact), with an average efficiency above 19 percent. This increased efficiency is a product of the new materials and a simple coating process for layers on the top and bottom of the device. Researchers showed it’s possible to create their solar cell in just seven steps.
In this study, the research team used a crystalline silicon core (or wafer) and applied layers of dopant-free type of silicon called amorphous silicon.
Then, they applied ultrathin coatings of a material called molybdenum oxide, also known as moly oxide, at the sun-facing side of the solar cell, and lithium fluoride at the bottom surface. The two layers, having thicknesses of tens of nanometers, act as dopant-free contacts for holes and electrons, respectively.
„Moly oxide and lithium fluoride have properties that make them ideal for dopant-free electrical contacts,” said Ali Javey, program leader of Electronic Materials at Berkeley Lab and a professor of Electrical Engineering and Computer Sciences at UC Berkeley.
Both materials are transparent, and they have complementary electronic structures that are well-suited for solar cells.
„They were previously explored for other types of devices, but they were not carefully explored by the crystalline silicon solar cell community,” said Javey, the lead senior author of the study.
Javey noted that his group had discovered the utility of moly oxide as an efficient hole contact for crystalline silicon solar cells a couple of years ago. „It has a lot of defects, and these defects are critical and important for the arising properties. These are good defects,” he said.
Stefaan de Wolf, another author who is team leader for crystalline silicon research at EPFL in Neuchâtel, Switzerland, said, „We have adapted the technology in our solar cell manufacturing platform at EPFL and found out that these moly oxide layers work extremely well when optimized and used in combination with thin amorphous layer of silicon on crystalline wafers. They allow amazing variations of our standard approach.”
In the study, the team identified lithium fluoride as a good candidate for electron contacts to crystalline silicon coated with a thin amorphous layer. That layer complements the moly oxide layer for hole contacts.
The team used a room-temperature technique called thermal evaporation to deposit the layers of lithium fluoride and moly oxide for the new solar cell. There are many other materials that the research teams hopes to test to see if they can improve the cell’s efficiency.
Javey said there is also promise for adapting the material mix used in the solar cell study to improve the performance of semiconductor transistors. „There’s a critical need to reduce the contact resistance in transistors so we’re trying to see if this can help.”
Source: Lawrence Berkeley National Laboratory

Lăsați-i să vă vadă transpirația: Ce senzori noi pot dezvălui din transpirație(Let them see you sweat:What new wearable sensors can reveal from perspiration)

este un sistem flexibil de senzori care poate măsura metaboliții și electroliții în transpirație, poate calibra datele pe baza temperaturii pielii și poate sincroniza rezultatele în timp real cu un smartphone

76 sept