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Spin control: New technique sorts nanotubes by length
May 19, 2008Researchers at the National Institute of Standards and Technology (NIST) have reported a new technique to sort batches of carbon nanotubes by length using high-speed centrifuges. Many potential applications for carbon nanotubes depend on the lengths of these microscopic cylinders, and one of the most important features of the new technique, say the scientists, is that it should be easily scalable to produce industrial quantities of high-quality nanotubes.
So-called single wall carbon nanotubes (SWCNTs) are essentially sheets of carbon atoms only one atom thick that have rolled themselves into tubes with a diameter of approximately one nanometer. They have unique combinations of thermal, mechanical, optical and electronic properties that suggest a wide variety of uses, including circuit elements in molecular electronics, fluorescent tags for diagnostic and therapeutic applications in medicine and light sources for compact, efficient flat-panel displays, among many others.
Unfortunately, the methods for manufacturing carbon nanotubes always create a large percentage of nanojunk in the mix-clumps of carbon, ordinary soot, particles of metal used as a catalyst-and nanotubes come in an enormous range of lengths, from a few tens or hundreds, up to thousands of nanometers. Refining the lot is essential for most uses. For many potential applications, nanotubes need to be separated by length. In biomedical applications, for example, it has been shown that whether or not nanotubes are taken up in cells depends critically on length (see "Study: Cells Selectively Absorb Short Nanotubes.") Nanotubes used as components in future microcircuits obviously need to fit in place, and in optical applications, a nanotube's length determines how strongly it will absorb or emit light (see "Longer is Better for Nanotube Optical Properties.")
In 2006, researchers found that you could separate nanotubes by "chirality" (a measure of the twist in the carbon atom sheet) by spinning them in a dense fluid in an ultracentrifuge tube because of a relationship between chirality and buoyancy. In this new work, a team of NIST researchers demonstrated that a variation of the same technique can separate nanotubes by length. They showed that while the nanotubes ultimately will move to a point of equilibrium in the centrifuge tube dictated by their buoyancy, due to friction they will move at different rates depending on their lengths.
"When we spin the centrifuge, it turns out that the longer ones move faster. We basically just run a race and the longer ones move farther in the same amount of time," says researcher Jeffrey Fagan, "Eventually they get separated enough in position that we can just pull off layers and get different lengths."
What's particularly exciting, they say, is that while other techniques have been shown to sort nanotubes by length, this is the first approach that could be scaled up to produce commercially important quantities of nanotubes in a given length range. The process also removes much of unwanted junk-particularly metal particles-from the batch. NIST has applied for a patent on the process.
National Institute of Standards and Technology (NIST)
In 2006, researchers found that you could separate nanotubes by "chirality" (a measure of the twist in the carbon atom sheet) by spinning them in a dense fluid in an ultracentrifuge tube because of a relationship between chirality and buoyancy. In this new work, a team of NIST researchers demonstrated that a variation of the same technique can separate nanotubes by length. They showed that while the nanotubes ultimately will move to a point of equilibrium in the centrifuge tube dictated by their buoyancy, due to friction they will move at different rates depending on their lengths.
"When we spin the centrifuge, it turns out that the longer ones move faster. We basically just run a race and the longer ones move farther in the same amount of time," says researcher Jeffrey Fagan, "Eventually they get separated enough in position that we can just pull off layers and get different lengths."
What's particularly exciting, they say, is that while other techniques have been shown to sort nanotubes by length, this is the first approach that could be scaled up to produce commercially important quantities of nanotubes in a given length range. The process also removes much of unwanted junk-particularly metal particles-from the batch. NIST has applied for a patent on the process.
National Institute of Standards and Technology (NIST)
Carbon Nanotube News and Current Carbon Nanotube Events RSSTrue properties of carbon nanotubes measured
For more than 15 years, carbon nanotubes (CNTs) have been the flagship material of nanotechnology. Researchers have conceived applications for nanotubes ranging from microelectronic devices to cancer therapy. Their atomic structure should, in theory, give them mechanical and electrical properties far superior to most common materials.
Golden Scales: Nanoscale Mass Sensor from Berkeley Can Be Used to Weigh Individual Atoms and Molecules
There's a new "gold standard" in the sensitivity of weighing scales. Using the same technology with which they created the world's first fully functional nanotube radio, researchers with Berkeley Lab and the University of California (UC) at Berkeley have fashioned a nanoelectromechanical system (NEMS) that can function as a scale sensitive enough to measure the mass of a single atom of gold.
'Nanonet' circuits closer to making flexible electronics reality
Researchers have overcome a major obstacle in producing transistors from networks of carbon nanotubes, a technology that could make it possible to print circuits on plastic sheets for applications including flexible displays and an electronic skin to cover an entire aircraft to monitor crack formation.
The fight for the best quantum bit (qubit)
Our results give us, for the first time, the possibility to understand the interaction between just two electrons placed next to each other in a carbon nanotube.
Perfecting a solar cell by adding imperfections
Nanotechnology is paving the way toward improved solar cells. New research shows that a film of carbon nanotubes may be able to replace two of the layers normally used in a solar cell, with improved performance at a lower cost. Researchers have found a surprising way to give the nanotubes the properties they need: add defects.
Brown researchers work toward ending cartilage loss
Scientists have long wrestled with how to aid those who suffer cartilage damage and loss. One popular way is to inject an artificial gel that can imitate cartilage's natural ability to act as the body's shock absorber. But that solution is temporary, requiring follow-up injections.
Researchers create the first thermal nanomotor in the world
Researchers from the UAB Research Park have created the first nanomotor that is propelled by changes in temperature. A carbon nanotube is capable of transporting cargo and rotating like a conventional motor, but is a million times smaller than the head of a needle.
Carbon nanotubes made into conductive, flexible 'stained glass'
Carbon nanotubes are promising materials for many high-technology applications due to their exceptional mechanical, thermal, chemical, optical and electrical properties.
Memory in artificial atoms
Three of our nano-physicists have made a discovery that can change the way we store data on our computers. This means that in the future we can store data much faster, and more accurate. Their discovery has been published in the scientific journal Nature Physics.
The future of computing -- carbon nanotubes and superconductors to replace the silicon chip
The future of computing is under the spotlight at the Institute of Physics' Condensed Matter and Materials Physics conference at the Royal Holloway College of the University of London on 26-28 March.
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