Showing Spotlights 449 - 456 of 534 in category All (newest first):
Current production methods for carbon nanotubes (CNT) result in units with different diameter, length, chirality and electronic properties, all packed together in bundles, and often blended with some amount of amorphous carbon. The separation of nanotubes according to desired properties remains a technical challenge. Especially single-walled carbon nanotube (SWCNT) sorting is a challenge because the composition and chemical properties of SWCNTs of different types are very similar, making conventional separation techniques inefficient. In order to find ways to control nanotube diameter and chirality it would be necessary to monitor nanotube growth. Then, if one knew exactly how to grow nanotubes of different characteristics, one could control their electronic properties because, depending on the way the carbon atoms are arrange around the 'waist' of a nanotube, the electronic properties could vary from metallic to semiconducting. An international group of researchers has demonstrated a novel approach to use nanotubes as reaction cells, enabling them to monitor the birth and growth of carbon nanotubes, and taking some spectacular image of this process.
May 10th, 2007
Back in 1756, the German physicist Johann Gottlob Leidenfrost published a manuscript titled De Aquae Communis Nonnullis Qualitatibus Tractatus ("A Tract About Some Qualities of Common Water") in which he described a phenomenon in which a liquid, in near contact with a mass significantly hotter than its boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly. This effect came to be called the "Leidenfrost Effect" and the associated temperature point the "Leidenfrost Temperature." An everyday example of this can be seen in your own kitchen: sprinkle a drop of water in a hot skillet - if the skillet's temperature is at or above the Leidenfrost Temperature, the water skitters across the metal and takes longer to evaporate than it would in a skillet that is hot, but at a temperature below the Leidenfrost point. Researchers in Germany have used this effect for a novel, template-free synthesis and patterning method of nanostructures.
May 9th, 2007
One of the newly emerging areas of semiconductor technology is the field of transparent electronics. These thin-film materials hold the promise of a new class of flexible and transparent electronic components that would be more environmentally benign than current electronics. Being able to print transparent circuits on low-cost, flexible, plastic substrates opens up the possibility of a wide range of new applications, ranging from windshield displays and flexible solar cells to clear toys and artificial skins and even sensor implants. It is likely that such flexible see-through structures will find wide uses in military, biosensing and consumer goods due to the advantages of high transparency and reliable electrical characteristics. However, the emerging transparent electronics technology is facing manufacturing problems: current fabricating processes do not separate the device manufacturing from material synthesis. The transparent electronic materials, which are largely inorganic oxides. are directly deposited on the device substrate under harsh conditions which may cause damage to the existing layer or flexible substrate. The etching of small dimension oxide multilayer is also difficult due to the low selectivity of the etching recipe. New research results demonstrate that nanofabrication techniques could solve these problems.
Apr 30th, 2007
The promise of revolutionary bottom-up nanotechnology is based on a vision of molecular assembly technologies where nanoscale materials and structures self-assemble to microscale structures and finally to macroscopic devices and products. We are a long way from realizing this vision but researchers are busily laying the foundation for the things to come. Assembling nanoscopic components into macroscopic materials has been an appealing goal but one of the enormous difficulties lies in bridging approximately six orders of magnitude that separate the nanoscale from the macroscopic world. New research at Northwestern University in the U.S. helps to overcomes this difficulty by dividing the assembly process into two manageable sub-steps. First, nanoparticles are assembled into larger, 100 nm-size, spherical building blocks, which are both deformable and "sticky" towards one another. Once assembled, these components "glue" together like pieces of clay to give millimeter or even centimeter-sized structures. The novelty of this technique is both the hierarchical assembly approach (i.e., atoms to nanoparticles to supraspheres to macroscopic materials) and the resulting "soft" structures, which contrast with previously reported hard and brittle nanoparticles assemblies/crystals. This research takes a further step in making nanoscale discoveries relevant to our everyday - macroscopic - world.
Apr 25th, 2007
Self assembled structures from colloidal particles have many applications in biology, as chemical sensors and as photonic crystals. The control of shape and valency of the colloidal particle is very important since it will determine the 3D lattices of the assembled structure. There have been several prior effort to fabricating particles with complex shapes. Most particles with anisotropic shape are from the simple assembly of spheres or the modification of spherical particles. Interference lithography is one of the few techniques which can provide direct and systematic control over symmetry and volume fraction of the 3D structure. It involves the simple creation of interference patterns in a photoresist systems and subsequent pinch off of the parent structure through a drying process. Researchers at MIT have now presented a new facile and high-yield route for the fabrication of highly nonspherical complex multivalent nanoparticles. This technique exploits the ability of holographic interference lithography to control network topology. These research results could lay the groundwork for establishing and demonstrating control over particle shape in colloidal nanoparticles.
Apr 17th, 2007
Research into the subject of radiation damage in graphite began in the early 1940s as a part of the development of nuclear weapons and nuclear power. Some designs of nuclear power reactors, such as the Chernobyl reactors, use graphite as moderator (the material which slows down the neutrons released from fission so that they cause more fission). The damage to the graphite moderators caused by radiation has been one of the major concerns of the nuclear power industry and radiation defects, i.e. structural irregularities, in graphite produced upon irradiation, their structure, properties and formation mechanisms, have been subject of intense research. Several years ago, defects in carbon materials became a hot topic again but now in the context of carbon layered nanostructures, such as multiwalled and bundled carbon nanotubes, which closely resemble graphite in their structure. The formation of irradiation-induced defects in graphite like layered carbon nanostructures, multiwalled and bundled carbon nanotubes, nanoonions, etc. changes their mechanical and electronic properties and may even trigger dramatic structural changes. While the terms "radiation damage" and "defect" are perceived negatively by people, the nanoengineering research community is trying to make use of defect structures for the deliberate modification of carbon nanomaterials, which can eventually be used in the manufacturing of nanoelectromechanical systems (NEMS). This process is sometimes called "defect-assisted engineering."
Apr 13th, 2007
Super-tough materials with exceptional mechanical properties are in critical need for applications under extreme conditions such as jet engines, power turbines, catalytic heat exchangers, military armors, aircrafts, and spacecrafts. Researchers involved in improving man-made composite materials are trying to understand how some of the amazing high-performance materials found in Nature can be copied or even improved upon. Nature has evolved complex bottom-up methods for fabricating ordered nanostructured materials that often have extraordinary mechanical strength and toughness. One of the best examples is nacre, the pearly internal layer of many mollusc shells. It has evolved through millions of years to a level of optimization currently achieved in very few engineered composites. In a novel approach, scientists have prepared a high-performing nanocomposite material that takes advantage of two different exceptional natural materials - layered nacre and the marine adhesive of mussels. The resulting nanostructured composite film exhibits high strength exceeding that of even nacre.
Apr 3rd, 2007
Proteins are very specific about which other proteins or biochemicals they will interact with and therefore are of great use for biosensing applications. For instance, if a malignant cancer develops in the human body, the cancer cells produce certain types of proteins. Identifying such proteins enables early detection of cancer. One of the goals of nanobiotechnology is to develop protein chips that are sensitively responsive to a very tiny amount of specific proteins in order to enable such early stage diagnosis. For example, a protein that is known to bind to a protein produced by a cancer cell could be attached to a biochip. If this particular cancer cell protein were present in a sample passed over the chip, it would bind to the protein on the chip, causing a detectable change in the electrical signal passing through the chip. This change in the electrical signal would be registered by the device, confirming the presence of the protein in the sample. While this sounds very promising for the future of diagnostic systems, with the promise of protein chips capable of single-molecule resolution, the controlled assembly of proteins into bioactive nanostructures still is a key challenge in nanobiotechnology. Researchers in Germany took a further step towards this goal by developing a native protein nanolithography technique that allows for the nanostructured assembly of even fragile proteins.
Apr 2nd, 2007