Lună: aprilie 2016

Nanotuburile se aliniază pentru a forma filme

Filmele subțiri oferă posibilități de a realiza dispozitive flexibile electronice și fotonice (manipularea luminii)

Posted: Apr 04, 2016

Nanotubes line up to form films

(Nanowerk News) A simple filtration process helped Rice University researchers create flexible, wafer-scale films of highly aligned and closely packed carbon nanotubes.
Scientists at Rice, with support from Los Alamos National Laboratory, have made inch-wide films of densely packed, chirality-enriched single-walled carbon nanotubes through a process revealed today in Nature Nanotechnology („Wafer-scale monodomain films of spontaneously aligned single-walled carbon nanotubes”).
A scanning electron microscope image shows highly aligned and closely packed carbon nanotubes
A scanning electron microscope image shows highly aligned and closely packed carbon nanotubes gathered into a film by researchers at Rice University. (Image: Kono Lab/Rice University)
In the right solution of nanotubes and under the right conditions, the tubes assemble themselves by the millions into long rows that are aligned better than once thought possible, the researchers reported.
The thin films offer possibilities for making flexible electronic and photonic (light-manipulating) devices, said Rice physicist Junichiro Kono, whose lab led the study. Think of a bendable computer chip, rather than a brittle silicon one, and the potential becomes clear, he said.
„Once we have centimeter-sized crystals consisting of single-chirality nanotubes, that’s it,” Kono said. „That’s the holy grail for this field. For the last 20 years, people have been looking for this.”
The Rice lab is closing in, he said, but the films reported in the current paper are „chirality-enriched” rather than single-chirality. A carbon nanotube is a cylinder of graphene, with its atoms arranged in hexagons. How the hexagons are turned sets the tube’s chirality, and that determines its electronic properties. Some are semiconducting like silicon, and others are metallic conductors.
A film of perfectly aligned, single-chirality nanotubes would have specific electronic properties. Controlling the chirality would allow for tunable films, Kono said, but nanotubes grow in batches of random types.
highly aligned nanotube films
Rice University researchers discovered a method to make highly aligned nanotube films. The films may become valuable for flexible electronics and photonic devices. (Image: Jeff Fitlow/Rice University)
For now, the Rice researchers use a simple process developed at the National Institute of Standards and Technology to separate nanotubes by chirality. While not perfect, it was good enough to let the researchers make enriched films with nanotubes of different types and diameters and then make terahertz polarizers and electronic transistors.
The Rice lab discovered the filtration technique in late 2013 when graduate students and lead authors Xiaowei He and Weilu Gao inadvertently added a bit too much water to a nanotube-surfactant suspension before feeding it through a filter assisted by vacuum. (Surfactants keep nanotubes in a solution from clumping.)
The film that formed on the paper filter bore further investigation. „Weilu checked the film with a scanning electron microscope and saw something strange,” He said. Rather than drop randomly onto the paper like pickup sticks, the nanotubes – millions of them – had come together in tight, aligned rows.
„That first picture gave us a clue we might have something totally different,” He said. A year and more than 100 films later, the students and their colleagues had refined their technique to make nanotube wafers up to an inch wide (limited only by the size of their equipment) and of any thickness, from a few to hundreds of nanometers.
Further experiments revealed that each element mattered: the type of filter paper, the vacuum pressure and the concentration of nanotubes and surfactant. Nanotubes of any chirality and diameter worked, but each required adjustments to the other elements to optimize the alignment.
The films can be separated from the paper and washed and dried for use, the researchers said.
They suspect multiwalled carbon nanotubes and non-carbon nanotubes like boron nitride would work as well.
Co-author Wade Adams, a senior faculty fellow at Rice who specializes in polymer science, said the discovery is a step forward in a long quest for aligned structures.
„They formed what is called a monodomain in liquid crystal technology, in which all the rigid molecules line up in the same direction,” Adams said. „It’s astonishing. (The late Rice Nobel laureate) Rick Smalley and I worked very hard for years to make a single crystal of nanotubes, but these students have actually done it in a way neither of us ever imagined.”
Why do the nanotubes line up? Kono said the team is still investigating the mechanics of nucleation – that is, how the first few nanotubes on the paper come together. „We think the nanotubes fall randomly at first, but they can still slide around on the paper,” he said. „Van der Waals force brings them together, and they naturally seek their lowest-energy state, which is in alignment.” Because the nanotubes vary in length, the researchers suspect the overhangs force other tubes to line up as they join the array.
The researchers found their completed films could be patterned with standard lithography techniques. That’s yet another plus for manufacturers, said Kono, who started hearing buzz about the discovery months before the paper’s release.
„I gave an invited talk about our work at a carbon nanotube conference, and many people are already trying to reproduce our results,” he said. „I got so much enthusiastic response right after my talk. Everybody asked for the recipe.”
Source: Rice University

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Noutăți noi de sticlă metalică

Inginerii au creat un material nou cu o structură chimică neobișnuită care îl face incredibil de greu și totuși elastic.
Materialul poate rezista la impacturi grele fără a se deforma – chiar și atunci când este împins dincolo de limitele sale elastice, nu rupe, în schimb își păstrează cea mai mare parte a rezistenței sale inițiale. Acest lucru îl face posibil să fie util într-o varietate de aplicații, de la burghie la armura pentru soldați până la căptușeli rezistente la meteoriti pentru sateliți.

Posted: Apr 04, 2016

New metallic glass bounces (w/video)

(Nanowerk News) Engineers have created a new material with an unusual chemical structure that makes it incredibly hard and yet elastic.
The material can withstand heavy impacts without deforming – even when pushed beyond its elastic limits, it doesn’t fracture, instead retaining most of its original strength. That makes it potentially useful in a variety of applications from drill bits to body armor for soldiers to meteor-resistant casings for satellites.
In the journal Scientific Reports („Shock Wave Response of Iron-based In Situ Metallic Glass Matrix Composites”), researchers from USC; the University of California, San Diego; and Caltech announced the creation of the material, which was produced by heating a powdered iron composite up to exactly 630 degrees Centigrade (1166 degrees Faherenheit) and then rapidly cooling it.
Bulk Metallic Glass (left) and Steel (right)
„In particular, the fact that the new materials performed so well under shock loading was very encouraging and should lead to plenty of future research opportunities,” said Veronica Eliasson, lead author of the paper and assistant professor at the USC Viterbi School of Engineering.
Dubbed SAM2X5-630, the new material has the highest impact resistance of any „bulk metallic glass” – a class of artificially generated materials first discovered in the 1960s that possess disproportionate strength, resilience, and elasticity due to their unusual chemical structure.
Typical metals and metal alloys have an organized, crystalline structure at the atomic level. Bulk metal glasses (BMGs, for short) are formed when metal and metal alloys are subjected to extreme heat and then rapidly cooled – exciting their atoms into disorganized arrangements, and then freezing them there.
In general, BMGs tend to be strong, resist scratching, tough to fracture, and highly elastic. One commercially available zirconium-based BMG is pound-for-pound twice as strong as titanium.
„Thanks to Professor Eliasson’s expertise in shocks and high velocity testing, we were able to observe the remarkable elastic limit of this material at high velocities, a behavior which was not evident from conventional mechanical tests,” said Andrea Hodge, principle investigator of the project and professor at USC Viterbi.
What makes SAM2X5-630 special is that it’s not entirely a glass – just mostly. For some reason, the exact timing and temperatures used to create it leave just a few hints of structure here and there – which seems to be the key to its unique nature. The exact same iron composite heated and cooled slightly differently yields a completely random atomic arrangement that lacks the impressive elastic properties.
„It has almost no internal structure, like glass, but you see tiny regions of crystallization,” Eliasson said. „We have no idea why a small amount of crystalline regions in these bulk metallic glasses makes such a big difference under shock loading.”
The Hugoniot Elastic Limit (the maximum shock it can take without irreversibly deforming) of a 1.5-1.8 mm-thick piece of SAM2X5-630 was measured at 11.76 ± 1.26 GPa.
For reference, stainless steel has an elastic limit of 0.2 GPa, while that of tungsten carbide (a high-strength ceramic used in military armor) is 4.5 GPa. This isn’t to say that SAM2X5-630 has the highest elastic limit of any material known; diamonds top out at a whopping 60 GPa, they’re just not practical for many real-world applications.
The material was produced at UC San Diego using a spark-plasma sintering process in which the iron compound is powdered, placed in a dye, and then zapped with a current – superheating it to the point of binding without ever liquefying it.
Eliasson and Hodge collaborated with former PhD student Gauri Khanolkar of USC, Michael Rauls of Caltech, and James Kelly and Olivia Graeve of the Jacobs School of Engineering at UC San Diego.
Source: University of Southern California

Read more: New metallic glass bounces (w/video)

SEADAM

cu scopul de a dezvolta o nouă generație de instrumente analitice capabile să detecteze oligoelemente la nivel de subfemtogramă, atât în atmosferă, cât și în fluidele corporale, pe baza know-how-ului consultantului tehnic

SEADM1

Rametele de nanotuburi Ruthenium deschid ușile pentru catalizatori mai buni

Procesul implică două etape, creștere și gravură. Practic, hcp ruteniu nu cresc în mod natural într-o structură cristalină a poate fi făcută într-un cadru nano. Deci, echipa de creștere direcționată ruteniu pe o sămânță de paladiu cu structura fcc, pe care ruteniu replicat. Apoi au îndepărtat miezul de paladiu, lăsând în urmă la fcc cadru ruteniu nano.
Pentru a asigura materialul a avut un potențial catalizator, echipa a fugit cadrele ruteniu nano prin mai multe teste de diagnostic: reducerea p-nitrofenol prin NaBH4 și dehidrogenarea boran amoniac. In timp ce este nevoie de mai multe date pentru a cuantifica cât de bine ruteniu deține împotriva catalizatorilor metalici existente, Xia spune ca rezultatele din experimentele lor sunt promițătoare.

Posted: Apr 01, 2016

Ruthenium nanoframes open the doors to better catalysts

(Nanowerk News) The world is run by catalysts. They clean up after cars, help make fertilizers, and could be the key to better hydrogen fuel. Now, a team of chemists, led by Xiaohu Xia from Michigan Technological University, has found a better way to make metal nanoframe catalysts.
Last week, Nano Letters („Ru Nanoframes with an fcc Structure and Enhanced Catalytic Properties”) published the team’s study, which covers how the researchers made a catalyst for the first time out of the noble metal ruthenium.
Ruthenium Nanoframe
Using a two-part process, chemist Xiaohu Xia and his team found a way to turn ruthenium into a nanoframe, a promising metal catalyst. (Image: Michigan Tech, Xiaohu Xia)
The effort brought together a team from Michigan Tech, the Argonne National Laboratory, University of Texas at Dallas, and Temple University. The team’s break-through is not limited to ruthenium, however. Xia says the process they developed is most important.
„We are fine-tuning the surface, size, shape and crystal structure,” he says. „Our goal is to increase their catalytic activity while reducing the usage of this precious material.”
The key is more surface area. Nanoframes, which are nanoparticles with open centers, have an advantage with their gazebo-like atomic arrangements.
Xia adds that not only shape but crystal structure is important, „Because catalytic reactions occur only on the surface of materials, the surface atom arrangement has a great impact on determining the catalytic activity.”
In general, ruthenium nanocrystals adopt the hexagonal close-packed (hcp) structure. But Xia and his team came up with an elegant solution for making ruthenium nanocrystals with another structure: face-centered cubic (fcc) structure.
The process involves two steps, growth and etching. Basically, hcp ruthenium doesn’t naturally grow in a crystal structure that can be made into a nanoframe. So, the team directed ruthenium growth on a palladium seed with an fcc structure, which the ruthenium replicated. Then they removed the palladium core, leaving behind an fcc ruthenium nanoframe.
To ensure the material had catalytic potential, the team ran the ruthenium nanoframes through several diagnostic tests: the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane. While more data is needed to quantify how well ruthenium holds up against existing metal catalysts, Xia says the results from their experiments are promising.
Once the material has been vetted, researchers will be able to start applying the catalyst to several big challenges. Namely, Xia says that ruthenium nanoframes and other catalysts with unique crystal structures could improve hydrogen fuel production and carbon storage.
Source: Michigan Technological University

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Cercetătorii folosesc tipărirea 3D pentru a crea structuri cu chimie activă

O limitare a cercetării este făcut pentru structura pentru imprimare, concentrația de nanoparticule necesare pentru a fi mai mică de 10 la sută din masa totală a structurii. Pentru a avea structura eficientă, ar putea fi necesară o concentrație mai mare, dar în funcție de necesitatea, 10 la suta ar putea fi OK, a spus Harting.
Structura tipărită pentru acest studiu a fost o formă simplă. Valorificând puterea de imprimare 3D, cercetatorii Urmatorul pas va fi de a imprima mai multe forme exotice pentru a înțelege modul în care structura imprimată Afectează reactivitatea chimic

Posted: Apr 01, 2016

Researchers use 3-D printing to create structure with active chemistry

(Nanowerk News) Many materials – sugars, thermoplastics, glass, metals, ceramics and more – are used to produce 3D-printed figures, typically with expensive or custom-built 3D printers.
For the first time, researchers have demonstrated how to use commercial 3D printers to create a structure with active chemistry. Led by Matthew Hartings, American University chemistry professor, researchers created a chemically active 3D-printed structure that acts to mitigate pollution. A study outlining the process published online today in Science and Technology of Advanced Materials („The chemical, mechanical, and physical properties of 3D printed materials composed of TiO2-ABS nanocomposites”).
And it’s OK to try this at home. The experiment, created with many off-the-shelf materials common to makers, hobbyists and home enthusiasts, puts the power of chemistry invention into the hands of people taking advantage of the 3D printing revolution.
The researchers designed a small structure the size of handheld sponge. They dispersed throughout plastic chemically active titanium dioxide (TiO2) nanoparticles. Using the same filament hobbyists use in the printing process of 3D-printed figures, researchers added the nanoparticles. Using a 3D thermoplastic printer, ubiquitous in manufacturing, the researchers printed a small, sponge-like plastic matrix.
Researchers had two questions: Would the nanoparticles stay active in the structure once printed? Created for pollution mitigation, would the matrix perform? The answers were yes.
Pollutants break down when natural light interacts with TiO2, which has potential applications in the removal of pollution from air, water and agricultural sources.
To demonstrate pollution mitigation, they placed the matrix in water and added an organic molecule (pollutant). The pollutant was destroyed. TiO2 also photocatalyzed the degradation of a rhodamine 6G in solution.
„It’s not just pollution, but there are all sorts of other chemical processes that people may be interested in. There are a variety of nanoparticles one could add to a polymer to print,” Hartings said.
One limitation of the research is that for the structure to print, the concentration of nanoparticles needed to be less than 10 percent of total mass of the structure. To have an efficient structure, a higher concentration could be needed, but depending on the need, 10 percent might be OK, Hartings said.
The structure printed for this study was a simple shape. Harnessing the power of 3D-printing, the researchers’ next step will be to print many exotic shapes to understand how printed structure affects the chemical reactivity.
Because of the promising results, they’ve already started experimenting with different printed geometries to determine an optimal printed shape for applications that involve photocatalytic removal of environmental pollutants.
Source: American University

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Pentagonul anunță un nou impuls pentru țesăturile „inteligente”(Pentagon announces new push for ‘smart’ fabrics)

pentru a crea textile inteligente care într-o zi ar putea vedea corturi din țesături generatoare de energie, pantofi de alergare la fel de ușor ca șosete și uniforme care detectează contaminarea chimică și nucleară

Pentagon