Paperwork: Buckypapers clarify electrical, optical behavior of nanotubesOctober 16, 2008Using highly uniform samples of carbon nanotubes-sorted by centrifuge for length-materials scientists at the National Institute of Standards and Technology (NIST) have made some of the most precise measurements yet of the concentrations at which delicate mats of nanotubes become transparent, conducting sheets. Their recent experiments* point up the importance of using relatively homogeneous-not overly short, but uniform in length- nanotubes for making high performance conducting films. Among their other qualities, single-wall carbon nanotubes (SWCNTs) have attracted much attention as tiny electrical conductors. Relatively small concentrations of nanotubes can change a normally insulating polymer film to a transparent electrical conductor. Potential applications range from transparent electrical shielding materials to futuristic flexible video displays, thin-film chemical sensors and other foldable electronics. One key design parameter for conductive films is the so-called "percolation threshold"-essentially the concentration at which random two- or three-dimensional networks of nanotubes first become electrically conducting. To test theories on how both the conductance and optical properties of such nanotube-infused films depend on the length of the tubes, the NIST team made samples of "buckypaper" by mixing nanotubes in water and draining the water away through nanoscale filters to leave behind a delicate nanotube mat. The highly refined, length-sorted nanotube samples were produced by an efficient technique developed earlier by the NIST group (see "Spin Control: New Technique Sorts Nanotubes by Length").
The NIST measurements validated one theory: buckypaper made of length-sorted carbon nanotubes closely follows the percolation theory for ideal two-dimensional sheets, with concentration threshold for conductivity getting lower as the tubes get longer. A sheet of 820 nanometer long nanotubes becomes conducting at an amazingly low 18 nanograms per square centimeter, the lowest yet reported. Interestingly, batches of short nanotubes or mixed-length batches form more three-dimensional networks that perform noticeably worse. On the other hand, predictions that optically the sheets would behave like thin metallic films turn out not to be the case. Optical properties are better predicted by the same general percolation theory, say the NIST researchers, which will provide a convenient theoretical framework for designing and engineering nanotech applications with these materials. National Institute of Standards and Technology (NIST) | |||||||||||||||||||||
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Related Nanotubes Current Events and Nanotubes News Articles The gold standard: Biodesign Institute researchers use nanoparticles to make 3-D DNA nanotubes Arizona State University researchers Hao Yan and Yan Liu imagine and assemble intricate structures on a scale almost unfathomably small. Their medium is the double-helical DNA molecule, a versatile building material offering near limitless construction potential. Researchers make breakthrough in the production of double-walled carbon nanotubes In recent years, the possible applications for double-walled carbon nanotubes have excited scientists and engineers, particularly those working on developing renewable energy technologies. Study on cytotoxicity of carbon nanotubes Owing to the novel properties of carbon nanotubes (CBNs), a series of problems associated with in vitro toxicity assessments of carbon nanotubes (CNTs) have appeared in many literatures. Pitt Researchers Create Nontoxic Clean-up Method for Common, Potentially Toxic Nano Materials University of Pittsburgh researchers have developed the first natural, nontoxic method for biodegrading carbon nanotubes, a finding that could help diminish the environmental and health concerns that mar the otherwise bright prospects of the super-strong materials commonly used in products, from electronics to plastics. USC researchers print dense lattice of transparent nanotube transistors on flexible base It's a clear, colorless disk about 5 inches in diameter that bends and twists like a playing card, with a lattice of more than 20,000 nanotube transistors capable of high-performance electronics printed upon it using a potentially inexpensive low-temperature process. New Hybrid Nanostructures Detect Nanoscale Magnetism A key challenge of nanotechnology research is investigating how different materials behave at lengths of merely one-billionth of a meter. When shrunk to such tiny sizes, many everyday materials exhibit interesting and potentially beneficial new properties. As Sticky as a Gecko ... but Ten Times Stronger! The gecko's amazing ability to stick to surfaces and walk up walls has inspired many researchers to manufacture materials that mimic the special surface of a gecko's foot. Simulations help explain fast water transport in nanotubes By discovering the physical mechanism behind the rapid transport of water in carbon nanotubes, scientists at the University of Illinois have moved a step closer to ultra-efficient, next-generation nanofluidic devices for drug delivery, water purification and nano-manufacturing. Coating improves electrical stimulation therapy used for Parkinson's, depression, chronic pain Researchers at UT Southwestern Medical Center have designed a way to improve electrical stimulation of nerves by outfitting electrodes with the latest in chemically engineered fashion: a coating of basic black, formed from carbon nanotubes. True 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. More Nanotubes Current Events and Nanotubes News Articles |
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