Showing Spotlights 1953 - 1960 of 2140 in category (newest first):
Novel and robust networks, tailored from nanostructures as building blocks, are the foundations for constructing nano- and microdevices. However, assembling nanostructures into ordered micronetworks remains a significant challenge in nanotechnology. The most suitable building blocks for assembling such networks are nanoparticle clusters, nanotubes and nanowires. Unfortunately, little is known regarding the different ways networks can be created and their physicochemical properties as a function of their architecture. It is expected that, when 1D nanostructures are connected covalently, the resulting assemblies possess mechanical, electronic, and porosity properties that are strikingly different from those of the isolated 1D blocks. In extensive theoretical studies, researchers now have shown that the properties of 2D and 3D networks built from 1D units are dictated by the specific architecture of these arrays. Specifically, they demonstrate that one could join nanotubes and make supernetworks that exhibit different properties when compared to the individual building blocks (i.e. the nanotubes). Besides the unique and unusual mechanical and electronic properties, the porosity of these systems makes them good candidates for exploring novel catalysts, sensors, filters, or molecular storage properties. The crystalline 2D and 3D networks are also expected to present unusual optical properties, in particular when the pore periodicity approaches the wavelength of different light sources, such as optical photonic crystals.
Jan 4th, 2007
Bacteria are ubiquitous in the earth's surface, subsurface, fresh water, and oceanic environment. Bacteria are remarkable in that they are capable of respiring aerobically and anaerobically using a variety of compounds, including metals, as terminal electron acceptors. Metal reducing bacteria can significantly affect the geochemistry of aquatic sediments, submerged soils, and the terrestrial subsurface. Microbial dissimilatory reduction of metals is a globally important biogeochemical process driving the cycling of iron and manganese, associated trace metals, and organic matte. Microbial metal reduction is of significant interest among scientists who are researching remediation of environmental contaminants. However, little is known about the biochemical or molecular mechanisms underlying bacterial metal reduction. Conducting research with toxic metal reducing bacteria, researchers discovered that bacteria produce electrically conductive nanowires in response to electron-acceptor limitation. These findings could be used to bioengineer electrical devices such as microbial fuel cells.
Jan 3rd, 2007
With its historic development tracing back to the Bronze Age, welding serves modern industry in broad areas such as construction, manufacturing, and engineering. Spot welding,a type of resistance welding used to weld various sheet metals, was originally developed in the early 1900s. The process uses two shaped copper alloy electrodes to concentrate welding current and force between the materials to be welded. The result is a small "spot" that is quickly heated to the melting point, forming a nugget of welded metal after the current is removed. Perhaps the most common application of spot welding is in the automobile industry, where it is used almost universally to weld the sheet metal forming a car. Spot welders can also be completely automated, and many of the industrial robots found on assembly lines are spot welders. With the continuing development of bottom-up nanotechnology fabrication processes, with self-assembly at its core, spot welding may likewise play an important role in interconnecting carbon nanotubes (CNTs), nanowires, nanobelts, nanohelixes, and other nanomaterials and structures for the assembly of nanoelectronics and nanoelectromechanical systems (NEMS).
Jan 2nd, 2007
Animals that cling to walls and walk on ceilings owe this ability to micro- and nanoscale attachment elements. The highest adhesion forces are encountered in geckos. A gecko is the heaviest animal that can 'stand' on a ceiling, with its feet over its head. This is why scientists are intensely researching the adhesive system of the tiny hairs on its feet. On the sole of a gecko's toes there are some one billion tiny adhesive hairs, about 200 nanometers in both width and length. These hairs put the gecko in direct physical contact with its environment. The shape of the fibers is also significant; for example, spatula-shaped ends on the hairs provide particularly strong adhesion. Researching how insect and gecko feet have evolved to optimize adhesion strength is leading to bio-inspired development of artificial dry adhesive systems. Potential applications range from protective foil for delicate glasses to reusable adhesive fixtures - say goodbye to fridge magnets, here comes the hairy stuff, which will also stick to your mirror, your cupboard and your windows.
Dec 22nd, 2006
The controllable fabrication of highly ordered homogeneous nanostructures on surfaces remains a difficult challenge. Nevertheless, motivated by potential applications in micro- and optoelectronic devices, the problem of organic nanoscale structures on surfaces with long-range order and uniform size has attracted considerable attention in recent years. Researchers in Switzerland have now grown ordered arrays of fullerene nanochains on a gold surface. This demonstration constitutes a successful proof-of-principle for the concept of site-selective molecular anchoring on nanostructured template surfaces, and provides the perspective of fabricating complex supramolecular nanostructures being of potential technological relevance by site-selective anchoring and selfassembly methods using properly designed functional molecular building blocks.
Dec 21st, 2006
Gears, bearings, and liquid lubricants can reduce friction in the macroscopic world, but the origins of friction for small devices such as micro- or nanoelectromechanical systems (NEMS) require other solutions. Despite the unprecedented accuracy by which these devices are nowadays designed and fabricated, their enormous surface-volume ratio leads to severe friction and wear issues, which dramatically reduce their applicability and lifetime. Traditional liquid lubricants become too viscous when confined in layers of molecular thickness. This situation has led to a number of proposals for ways to reduce friction on the nanoscale, such as superlubricity and thermolubricity. Researchers in Switzerland now describe a resonance-induced superlubricity, which also occurs in many natural phenomena from biological systems to the motion of tectonic plates. This new method provides an efficient way to switch friction on and off at the atomic scale and, as a simple way of preventing mechanical damage without chemical contamination, could be of enormous importance for the development of NEMS.
Dec 20th, 2006
In recent years, the manipulation of single atoms and molecules has been a major advance in the application of the scanning tunneling microscope (STM). The main appeal of STM manipulation is the ability to access, control and modify the interactions between the tip and the adsorbate, a few angstroms apart. So far, however, atom manipulation using a STM or an AFM -tip has been restricted to flat surfaces. Manipulation of atoms on a rough terrain requires much more precise control at the atomic scale. Researchers now report extraction and manipulation of individual silver atoms on three dimensional silver nanoclusters. This is the first demonstration that individual atoms can be repeatedly pulled out from a silver cluster on a silver surface using STM tip. It is also the first atom manipulation work done on a 3-D surface. There are still very few research groups that have demonstrated single atom manipulation with atomic scale precision on flat surfaces. This remarkable achievement has an impact on the fundamental understanding of interactions between the matters. While it certainly is not a commercial production technique, it does further the fundamental understanding of the interaction between atoms, and it is an atom production technique that can be used to extract the atoms for atomistic construction.
Dec 19th, 2006
Drug intoxication, developed as a result of accidental overdosing, is a serious health problem. Drug overdoses are sometimes also caused intentionally to commit suicide, but many drug overdoses are usually the result of either irresponsible behavior, or the misreading of product labels. Other causes of overdose (especially heroin) include multiple drug use with counter indications (cocaine/amphetamines/alcohol) or use after a period of abstinence. According to the National Center for Health Statistics, in the U.S. alone almost 20,000 people a year die due to drug overdoses and accidental poisoning. While there has been a tremendous effort to develop drug delivery methods using nanotechnology, a new report shows that this could work the other way around as well, and that porous nanoparticles can soak up drug molecules in the body like a sponge. This could help to reduce fatalities from overdoses, according to tests showing that tiny spheres of poly(acrylic acid) can absorb substantial amounts of an antidepressant and an anesthetic in just a few minutes. In short, nanoparticles can act as potent antidotes!
Dec 18th, 2006