Showing Spotlights 2625 - 2632 of 2837 in category All (newest first):
Along the way to all-optical devices in communication and information technology, photonic crystals play a significant role. They form a basis material for the future realization of optical components and circuits, and maybe even complex optical circuits or optical computers. Examples include complex waveguides, integrated microcavities, channel drop filters, optical switches and low-threshold lasers. All such devices depend on the inclusion of defect structures, non-linear materials and/or light-emitters into photonic bandgap material. The combination of several devices into one photonic crystal would allow to realize the optical equivalent of an electronic circuit. So far, the intentional inclusion of such combined structures was very difficult to realize in practice, however. A group of German and Italian researchers now present a powerful technique that allows to create such photonic circuits inside photonic crystals by controlled micro-infiltration of liquid substances with sub-micron resolution. This approach forms an enabling technology for the realization of all optical devices and circuits.
Dec 14th, 2006
Due to the the increased use of modern bombs in terrorist attacks worldwide, where the amount of metal used is becoming very small, the development of a new approach capable of rapidly and cost-efficiently detecting volatile chemical emission from explosives is highly desirable and urgently necessary nowadays. The trained dogs and physical methods such as gas chromatography coupled to a mass spectrometer, nuclear quadrupole resonance, electron capture detection as well as electrochemical approaches are highly sensitive and selective, but some of these techniques are expensive and others are not easily fielded in a small, low-power package. As a complementary method, however, chemical sensors provide new approaches to the rapid detection of ultra-trace analytes from explosives, and can be easily incorporated into inexpensive and portable microelectronic devices. Researchers in PR China have developed a nanocomposite film that shows very fast fluorescence response to trace vapors of explosives such as TNT, DNT or NB.
Dec 13th, 2006
There is much discussion of molecules as components for future electronic devices and in recent years it has been possible to position single molecules in electrical junctions. Molecular and nanoscale structures have been shown to be capable of basic electronic functions such as rectification, negative differential resistance and single-electron transistor behavior. These observations show that molecular-electronic functions can be controlled through chemical manipulation. However, the contacts, the local environment and the temperature can all affect molecules' electrical properties. This sensitivity, particularly at the single-molecule level, may limit the use of molecules as active electrical components, and therefore it is important to design and evaluate molecular junctions with a robust and stable electrical response over a wide range of junction configurations and temperatures. A step in this direction, researchers in the UK now report an approach to monitor the electrical properties of single-molecule junctions, which involves precise control of the contact spacing and tilt angle of the molecule.
Dec 12th, 2006
A large portion of nanoscience and nanomaterial engineering is about trying to copy what has evolved in Nature. Take diatoms; a major group of hard-shelled algae and one of the most common types of phytoplankton. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica. Silicate materials are very important in nature and they are closely related to the evolution of living organisms. Diatom walls show a wide diversity in form, some quite beautiful and ornate, but usually consist of two symmetrical sides with a split between them, hence the group name. Diatomaceous earth consists of fossilized remains of diatoms and, as an environmentally friendly material, finds wide use especially in filter applications. It is also used as a mild abrasive, as a mechanical insecticide, as an absorbent for liquids, as an activator in blood clotting studies, and as a component of dynamite. As it is also heat-resistant, it can be used as a thermal insulator. Artificial synthesis of hollow cell walls of diatoms, as generally re-creating the silicate chemistry of Nature by chemical methods, is a key target of nanomaterial science. Researchers in Japan have now reported a method to produce artificial diatomaceous earth-like materials.
Dec 11th, 2006
There has been a great deal of interest in the toxicity of nanoparticles in the context of respiratory health. The responses of cells exposed to nanoparticles have been studied with regard to toxicity, but very little attention has been paid to the possibility that some types of particles can protect cells from various forms of lethal stress. Research has shown that nanoparticles composed of cerium oxide or yttrium oxide protect nerve cells from oxidative stress and that the neuroprotection is independent of particle size. This has led researchers to the conclusion that there is a potential for engineering this group of nanoparticles for therapeutic purposes.
Dec 8th, 2006
A large number of DNA-based nanomechanical devices have been described, controlled by a variety of methods: These include pH changes and the addition of other molecular components, such as small molecule effectors, proteins and DNA strands. The most versatile of these devices are those that are controlled by DNA strands: This versatility results because they can be addressed specifically by strands with particular sequences; these strands can be added to the solution directly, or perhaps they can result from another process ongoing within the local environment. Researchers have now shown that the state of a DNA-based nanomechanical device can be controlled by RNA strands, which means that nanomechanical devices could potentially be run from transcriptionally derived RNA molecules.
Dec 7th, 2006
The controlled synthesis of single-walled carbon nanotubes (SWCNTs), which generally requires a nanoscale catalyst metal, is crucial for their application to nanotechnology. In the chemical vapor deposition (CVD) of SWCNTs, the known effective catalyst species are the iron-family elements iron, cobalt, and nickel, with which a high SWCNT yield can be obtained. However, gold, silver, and copper have never been reported to produce SWCNTs. It is well known that iron, cobalt, and nickel have the catalytic function of graphite formation but that gold does not. The difference between the iron-family metals and gold is that the binding energy of carbon is much larger for the iron-family metals. Carbon atoms cannot stay on gold long enough to form a graphitic network. Thus, it is rather natural for iron, cobalt, and nickel to generate SWCNTs, but it is totally unexpected that gold would produce them too. The same picture is applicable to silver and copper. Nevertheless, researchers in Japan succeeded in developing a nanoparticle activation method that shows that even gold, silver, and copper act as efficient catalysts for SWCNT synthesis. These non-magnetic catalysts could provide new routes for controlling the growth of SWCNTs.
Dec 6th, 2006
Artificial photosynthesis, using solar energy to split water generating hydrogen and oxygen, is often considered a 'Holy Grail' of chemistry which can offer a clean and portable source of energy supply as durable as the sunlight. It takes about 2.5 volts to break a single water molecule down into oxygen along with negatively charged electrons and positively charged protons. It is the extraction and separation of these oppositely charged electrons and protons from water molecules that provides the electric power. The photocatalytic splitting of water into hydrogen and oxygen using solar light is a potentially clean and renewable source for hydrogen fuel. Although massive efforts have been made in this area, many researchers have faced different types of challenges reaching from fundamental sciences to engineering. Titanium dioxide has been considered one of the most promising photocatalytic materials due to its relatively low cost, chemical stability, and photostability. However, the catalytic property of titanium dioxide is limited with ultraviolet (UV) regions which accounts for only approx. 4% of the incoming solar energy and thus renders the overall process impractical. Tungsten trioxide has been recently focused on as a new photoanode material, or as a mixture material with titanium dioxide, for water splitting because the tungsten trioxide can offer relatively small band gap (approx. 2.5 eV) and corrosion stability in aqueous solution. Although tungsten trioxide has shown great potential such as photooxidation of water with visible light and high photocurrent with nanocrystals, the quantum yield is still low. In new research, titanium oxide nanotubes coated with tungsten oxide were prepared to harvest more solar light for the first time. The tungsten trioxide coatings significantly enhanced the visible spectrum absorption of the titanium dioxide nanotube array, as well as their solar-spectrum induced photocurrents.
Dec 5th, 2006
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