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Scientists from MIT have discovered that by coating carbon nanotubes in bee venom, they can create ultra-sensitive detectors for explosives such as TNT,
But the sensors arent just useful for explosives#the researchers found that the coated nanotubes can also detect two pesticides that contain nitro-aromatic compounds.
Despite the materials'present reliance on the mixed fortunes of the automobile industry, the market for carbon nanotubes as raw materials looks set to grow rapidly.
California, announced in June that its Beijing facility is now producing 500 tonnes of multiwalled nanotubes annually;
Many of these raw nanotubes are multiwalled, and are used to make light, strong, composite materials. But a host of smaller companies such as Nanocyl, based in Sambreville,
The cellulose nanocrystals represent a potential green alternative to carbon nanotubes for reinforcing materials such as polymers and concrete.
#Scientists scale terahertz peaks in nanotubescarbon nanotubes carry plasmonic signals in the terahertz range of the electromagnetic spectrum
In new research the Rice university laboratory of physicist Junichiro Kono disproved previous theories that dominant terahertz response comes from narrow-gap semiconducting nanotubes.
Knowing that metallic or doped nanotubes respond with plasmonic waves at terahertz frequencies opens up the possibility that the tubes can be used in a wide array of optoelectronic amplifiers detectors polarizers and antennas.
Scientists have long been aware of a terahertz peak in nanotubes the tiny cylinders of rolled-up carbon that show so much promise for advanced materials.
But experiments on batches of nanotubes which generally grow in a willy-nilly array of types failed to reveal why it was there.
Rice's growing expertise in separating nanotubes by type allowed Kono and his group to test for terahertz peaks in batches of pure metallic nanotubes known as armchairs as well as nonmetallic semiconducting tubes.
Metallic carbon nanotubes are expected to show plasmon resonance in the terahertz and infrared range but no group has demonstrated clearly the existence of plasmons in carbon nanotubes Zhang said.
Previously people proposed one possible explanation--that the terahertz peak is due to interband absorption in the small band gaps in semiconducting nanotubes.
We rejected that in this paper. Plasmons are free electrons on the surface of metals like gold silver
The researchers previously used this fact to demonstrate that aligned carbon nanotubes act as an excellent terahertz polarizer with performance better than commercial polarizers based on metallic grids.
Nanotubes can be thousands of times longer than they are wide and the ability to grow them
or to dope semiconducting nanotubes to add free carriers would make the tubes highly tunable for terahertz frequencies Kono said.
Tour's breakthrough unzipping technique for turning multiwalled carbon nanotubes into GNRS first revealed in Nature in 2009 has been licensed for industrial production.
and a bottom or hollow nanotubes that have an inside and outside. According to the portrait drawn from calculations by Yakobson and his group:*
*It has twice the tensile stiffness of graphene and carbon nanotubes and nearly three times that of diamond.*
For carbon that would be followed graphite by diamond then nanotubes then fullerenes. But nobody asks about the highest energy configuration.
#Waviness explains why carbon nanotube forests have low stiffnessa new study has found that waviness in forests of vertically-aligned carbon nanotubes dramatically reduces their stiffness answering a longstanding question surrounding the tiny structures.
Measurements of nanotube stiffness which is influenced by a property known as modulus had suggested that forests of vertically-aligned nanotubes should have a much higher stiffness than
and on buckling of the nanotubes under compression. However based on experiments scanning electron microscope SEM) imaging and mathematical modeling the new study found that kinked sections of nanotubes may be the primary mechanism reducing the modulus.
We believe that the mechanism making these nanotubes more compliant is a tiny kinkiness in their structure said Suresh Sitaraman a professor in the Woodruff School of Mechanical engineering at the Georgia Institute of technology.
Although they appear to be perfectly straight under high magnification we found waviness in the carbon nanotubes that we believe accounts for the difference in
what is measured versus what would be expected. The research which was supported by the Defense Advanced Research Projects Agency (DARPA) was published online August 31 2013 in the journal Carbon.
Carbon nanotubes provide many attractive properties including high electrical and thermal conductivity and high strength.
Individual carbon nanotubes have a modulus ranging from 100 gigapascals to 1. 5 terapascals. Arrays of vertically-aligned carbon nanotubes with a low density would be expected to a have an effective modulus of at least five to 150 gigapascals Sitaraman said
but scientists have measured typically values that are four orders or magnitude less--between one and 10 megapascals.
and Ph d. students Nicholas Ginga and Wei Chen studied forests of carbon nanotubes grown atop a silicon substrate then covered the tips of the structures with another layer of silicon.
They then used sensitive test apparatus--a nanoindenter--to compress samples of the nanotubes and measure their stiffness.
To look for potential explanations the researchers examined the carbon nanotubes using scanning electron microscopes located in Georgia Tech's Institute for Electronics and Nanotechnology facilities.
At magnification of 10000 times they saw the waviness in sections of the nanotubes. We found very tiny kinks in the carbon nanotubes said Sitaraman.
Although they appeared to be perfectly straight there was waviness in them. The more waviness we saw the lower their stiffness was.
They also noted that under compression the nanotubes contact one another influencing nanotube behavior. These observations were modeled mathematically to help explain what was being seen across the different conditions studied.
We took into account the contact between the carbon nanotubes said Chen. This allowed us to investigate the extreme conditions under which the deformation of nanotubes is constrained by the presence of neighboring nanotubes in the forest.
Though the loss of modulus might seem like a problem it actually may be helpful in thermal management applications Sitaraman said.
The compliance of the nanotubes allows them to connect to a silicon integrated circuit on one side
The flexibility of the nanotubes allows them to move as the top and bottom structures expand
The beauty of the carbon nanotubes is that they act like springs between the silicon chip
Carbon nanotubes have extraordinarily high thermal conductivity as much as ten times that of copper making them ideal for drawing heat away from the chips.
#Densest array of carbon nanotubes grown to datecarbon nanotubes'outstanding mechanical electrical and thermal properties make them an alluring material to electronics manufacturers.
The high density nanotubes might one day replace some metal electronic components leading to faster devices.
High-density forests are necessary for certain applications of carbon nanotubes like electronic interconnects and thermal interface materials he says.
Robertson and his colleagues grew carbon nanotubes on a conductive copper surface that was coated with co-catalysts cobalt and molybdenum.
#Bismuth-carrying nanotubes show promise for CT scansscientists at Rice university have trapped bismuth in a nanotube cage to tag stem cells for X-ray tracking.
Rice chemist Lon Wilson and his colleagues are inserting bismuth compounds into single-walled carbon nanotubes to make a more effective contrast agent for computed tomography (CT) scanners.
But this is the first time anyone has combined bismuth with nanotubes to image individual cells he said.
if we put bismuth inside the nanotubes and the nanotubes inside stem cells we might be able to track them in vivo in real time.
Experiments to date confirm their theory. In tests using pig bone marrow-derived mesenchymal stem cells Wilson
and lead author Eladio Rivera a former postdoctoral researcher at Rice found that the bismuth-filled nanotubes which they call Bi@US-tubes produce CT images far brighter than those from common
and purifies the nanotubes. When the tubes and bismuth chloride are mixed in a solution they combine over time to form Bi@US-tubes.
The nanotubes are lipophilic so when they find each other in the cell they stick together. Wilson said his team's studies showed stem cells readily absorb Bi@US-tubes without affecting their function The cells adjust over time to the incorporation of these chunks of carbon
Once the bismuth is encapsulated in the nanotubes the agent can produce high contrast in very small concentrations.
Bismuth ions appear to get into the nanotubes by capillary action and we think we can improve on the process to at least double the contrast maybe more he said.
The Tour lab pioneered the bulk manufacture of single-atom-thick graphene nanoribbons in 2009 with the discovery that carbon nanotubes could be unzipped chemically into long thin sheets.
#Broadband photodetector for polarized lightusing carpets of aligned carbon nanotubes researchers from Rice university and Sandia National Laboratories have created a solid-state electronic device that is hardwired to detect polarized light across a broad swath of the visible and infrared spectrum.
In February Kono L onard and colleagues described a new method for making photodetectors from carpets of carbon nanotubes--long narrow tubes of pure carbon that are about as wide as a strand of DNA.
The nanotube carpets used in the photodetectors are grown in the lab of Rice chemist Robert Hauge who pioneered a process for growing densely packed nanotubes on flat surfaces.
Xiaowei He a graduate student in Kono's group found a way to use Teflon film to flatten these tightly packed nanotubes
Each carpet contains dozens of varieties of nanotubes and about two-thirds of the varieties are semiconductors.
Because each of the semiconducting varieties interacts with a specific wavelength of light Kono's team was able to show in its earlier work that the flattened aligned carpets of nanotubes could serve as broad-spectrum photodetectors.
The wet-spinning process is similar to one recently used to create highly conductive fibers made of nanotubes but in this case Xiang just used water as the solvent rather than a super acid.
#Unzipped nanotubes unlock potential for batteriesresearchers at Rice university have come up with a new way to boost the efficiency of the ubiquitous lithium ion (LI) battery by employing ribbons of graphene that start as carbon nanotubes.
Tour and his colleagues developed a method for unzipping nanotubes into GNRS revealed in a 2009 cover story in Nature.
since graphene (and its cousin material carbon nanotubes) is the only material with the high strength-to-weight ratio required for this kind of hypothetical application.
#Diamonds, nanotubes find common ground in graphenewhat may be the ultimate heat sink is only possible because of yet another astounding capability of graphene.
The one-atom-thick form of carbon can act as a go-between that allows vertically aligned carbon nanotubes to grow on nearly anything.
The same could be said of carbon nanotubes which are basically rolled-up tubes of graphene. A vertically aligned forest of carbon nanotubes grown on diamond would disperse heat like a traditional heat sink but with millions of fins.
Such an ultrathin array could save space in small microprocessor-based devices. Further work along these lines could produce such structures as patterned nanotube arrays on diamond that could be utilized in electronic devices Ajayan said.
Graphene and metallic nanotubes are also highly conductive in combination with metallic substrates they may also have advanced uses in electronics he said.
which the nanotubes grow. The researchers think graphene facilitates nanotube growth by keeping the catalyst particles from clumping.
but decided to look at liquid crystal silicones without the nanotubes first. It's always better to start simple Verduzco said.
The phenomenal properties of carbon nanotubes have enthralled scientists from the moment of their discovery in 1991.
Nanotubes'conductive properties--for both electricity and heat--rival the best metal conductors. They also can serve as light-activated semiconductors drug-delivery devices
Unfortunately carbon nanotubes are also the prima donna of nanomaterials; they are difficult to work with despite their exquisite potential.
For starters finding the means to produce bulk quantities of nanotubes took almost a decade.
Scientists also learned early on that there were several dozen types of nanotubes--each with unique material and electrical properties;
Creating large-scale objects from these clumps of nanotubes has been a challenge. A threadlike fiber that is less than one-quarter the thickness of a human hair will contain tens of millions of nanotubes packed side by side.
Ideally these nanotubes will be aligned perfectly--like pencils in a box--and tightly packed. Some labs have explored means of growing such fibers whole
but the production rates for these solid-state fibers have proven quite slow compared with fiber-production methods that rely on a chemical process called wet spinning.
In this process clumps of raw nanotubes are dissolved in a liquid and squirted through tiny holes to form long strands.
The work established an industrially relevant wet-spinning process for nanotubes that was analogous to the methods used to create high-performance aramid fibers--like Teijin's Twaron
The fibers weren't very strong or conductive due partly to gaps and misalignment of the millions of nanotubes inside them.
and alignment of the carbon nanotubes in the fibers is said critical study co-author Yeshayahu Talmon director of Technion's Russell Berrie Nanotechnology Institute who began collaborating with Pasquali about five years ago.
when Talmon Pasquali and colleagues discovered the first true solvent for nanotubes--chlorosulfonic acid. For the first time scientists had a way to create highly concentrated solutions of nanotubes a development that led to improved alignment and packing.
Until that time no one thought that spinning out of chlorosulfonic acid was possible because it reacts with water Pasquali said.
and conductivity of spun fibers could also be improved if the starting material--the clumps of raw nanotubes--contained long nanotubes with few atomic defects.
In 2010 Pasquali and Talmon began experimenting with nanotubes from different suppliers and working with AFRL scientists to measure the precise electrical and thermal properties of the improved fibers.
The material is made of graphene nanoribbons atom-thick strips of carbon created by splitting nanotubes a process also invented by the Tour lab
Acid-free approach leads to strong conductive carbon threadsthe very idea of fibers made of carbon nanotubes is neat
The single-walled carbon nanotubes in new fibers created at Rice line up like a fistful of uncooked spaghetti through a process designed by chemist Angel Martã and his colleagues.
The tricky bit according to Martã whose lab reported its results this month in the journal ACS Nano is keeping the densely packed nanotubes apart before they're drawn together into a fiber.
Left to their own devices carbon nanotubes form clumps that are perfectly wrong for turning into the kind of strong conductive fibers needed for projects ranging from nanoscale electronics to macro-scale power grids Earlier research at Rice by chemist
and chemical engineer Matteo Pasquali a co-author on the new paper used an acid dissolution process to keep the nanotubes separated until they could be spun into fibers.
Matteo's group used chlorosulfonic acid to protonate the surface of the nanotubes Martã said.
A process revealed last year by Martã and lead authors Chengmin Jiang a graduate student and Avishek Saha a Rice alumnus starts with negatively charging carbon nanotubes by infusing them with potassium a metal and turning
otherwise dampen the nanotubes'ability to repel one another. Put enough nanotubes into such a solution and they're caught between the repellant forces
and an inability to move in a crowded environment Martã said. They're forced to align--a defining property of liquid crystals
and tightly binds the nanotubes together Martã said. But to make macroscopic materials the Martã team needed to pack many more nanotubes into the solution than in previous experiments.
As you start increasing the concentration the number of nanotubes in the liquid crystalline phase becomes more abundant than those in the isotropic (disordered) phase and that's exactly
what we needed Martã said. The researchers discovered that 40 milligrams of nanotubes per milliliter gave them a thick gel after mixing at high speed
and filtering out whatever large clumps remained. It's like a centrifuge together with a rotary drum Martã said of the mixing gear.
and the team is investigating ways to improve their electrical properties through doping the nanotubes with iodide.
which would have caused precipitation of the nanotubes he said. It turns out that this is not a showstopper
because we want the nanotubes to precipitate and stick to each other as soon as they exit the sealed system through the needle.
Researchers unzip nanotubes by shooting them at 15,000 mphcarbon nanotubes unzipped into graphene nanoribbons by a chemical process invented at Rice university are finding use in all kinds of projects
The Rice lab of materials scientist Pulickel Ajayan discovered that nanotubes that hit a target end first turn into mostly ragged clumps of atoms.
But nanotubes that happen to broadside the target unzip into handy ribbons that can be used in composite materials for strength
Until now we knew we could use mechanical forces to shorten and cut carbon nanotubes. This is the first time we have showed carbon nanotubes can be unzipped using mechanical forces.
The researchers fired pellets of randomly oriented multiwalled carbon nanotubes from a light gas gun built by the Rice lab of materials scientist Enrique Barrera with funding from NASA.
The pellets impacted an aluminum target in a vacuum chamber at about 15000 miles per hour. When they inspected the resulting carbon rubble they found nanotubes that smashed into the target end first
or at a sharp angle simply deformed into a crumpled nanotube. But tubes that hit lengthwise actually split into ribbons with ragged edges.
We were investigating possible applications for carbon nanotubes in space when we got this result.
Single-wall nanotubes do just the opposite; when the tube flattens the bottom wall hits the inside of the top wall
The researchers said 70 to 80 percent of the nanotubes in a pellet unzip to one degree or another.
They found it to be much better than nanofluids that contain higher amounts of oxide nitride or carbide ceramics metals semiconductors carbon nanotubes and other composite materials.
Theoretical physicist Boris Yakobson and his Rice colleagues found through exhaustive analysis that those who wish to control the chirality of nanotubes--the characteristic that determines their electrical properties--would be wise to look at other aspects of their growth.
To get a clear picture of how caps are related to nanotube chirality the Rice group embarked upon a detailed two-year census of the 4500 possible cap formations for nanotubes of just two diameters 0. 8
Nanotubes can be one or the other or the chiral angle can be anything in between with a shifting range of electrical properties.
Ideally scientists could grow the specific kinds of nanotubes they need for an application but in reality they grow as a random assortment that must then be separated with a centrifuge or by other means.
While individual nanotubes are capable of transmitting nearly 1000 times more current than copper the same tubes coalesced into a fiber using other technologies fail long before reaching that capacity.
Just a year ago the journal Science reported that Pasquali's lab in collaboration with scientists at the Dutch firm Teijin Aramid created a very strong conductive fiber out of carbon nanotubes.
Certain types of carbon nanotubes can carry far more electricity than copper. The ideal cable would be made of long metallic armchair nanotubes that would transmit current over great distances with negligible loss
but such a cable is not feasible because it's not yet possible to manufacture pure armchairs in bulk Pasquali said.
and materials scientists working on carbon nanotubes. That has generated some confusion in the literature over the right comparisons to make he said.
Dressed to kill, one atom at a time Nanotubes development could double battery life Nano-advances behind new architectural products Scientists create functioning transistor from a single atom
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