In our Spotlight from a few weeks ago - Nanopyramids - temporary resting places for light - we wrote about things like Q-factors, qubits, stopping light and other fascinating concepts and emerging techniques that could lead to quantum computing. Some of the feedback we received could be summarized with "Huh? Q-what...?" So today we'll take another look at the Quality (Q) factor of photonic-crystal nanocavities and the context it is relevant in. These 'nanocages' for light are currently the focus of much interest of nanotechnology research in photonics because they can strongly confine photons in a tiny space. Just as semiconductor crystals control the flow of electrons (the basis for all electronics), photonic crystals are a unique material used to construct photonic devices and circuits for manipulating light, i.e. photons. A prominent example of a photonic crystal is the naturally occurring gemstone opal. Photons (behaving as waves) propagate through it - or not - depending on their wavelength. Wavelengths of light (stream of photons) that are allowed to travel throught he crystal are known as "modes". Disallowed bands of wavelengths are called photonic band gaps. What's so interesting for researchers is that, once you are able to fully control and manipulate photons, you could not only vastly improve existing applications like optical data storage, high-precision sensing and telecommunications, but develop exotic technologies like quantum computing.
Every few months you can read about a recall of food items, be it fresh spinach of bottled infant formula, due to contamination with salmonella, E. coli or some other foodborne pathogen. A pathogen is a an organism that causes disease in another organism. The Centers for Disease Control and Prevention (CDC) estimates that foodborne diseases cause 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths each year. In 2000, the U.S. Department of Agriculture (USDA) estimated the costs associated with five major bacterial foodborne pathogens to be $6.9 billion. The Food and Drug Administration's 2005 Food Code states that the estimated cost of foodborne illness is $10-$83 billion annually. These staggering numbers, not to mention the potential of foodborne pathogens for terrorists attacks, are driving the development of biosensors as important analytical tools for the rapid detection of pathogens in the field, and they are increasingly playing a key role in controlling disease outbreaks. Immunosensors (biosensors that use antibodies as biological recognition elements) are of great interest because of their applicability (any compound can be analyzed as long as specific antibodies are available) and high sensitivity. High sensitivity, of course, is an important attribute in designing biosensors, but a large variance due to stochastic interaction between biomolecules, biosensor imperfections, and environmental variability (e.g., pH of the analyte) directly affects the reliability of the measured signal in almost all sensors. Researchers have now taken forward error-correction (FEC) techniques, already successfully applied for improving reliability of communication and storage systems such as CDs, and applied them to biosensors.
Yesterday we wrote about air bridges in nanotechnology fabrication. Today we show a practical example. Traditionally, electronic devices have been fabricated by top-down fabrication methods. Conducting polymers, for instance, have been synthesized as micro- and nanoscale fibers, tubes and wires for more than 10 years now. More recently, nanowires have been integrated into electronic circuits, making possible the development of devices such as polymer nanowire chemical sensors with superior performance. What most of these fabrication techniques have in common is that they are template-based (e.g. lithography or DNA templates) or depend on specialized fiber forming techniques such as electrospinning. However, as electronic components become smaller and smaller it is increasingly more difficult to use existing methods of fabrication. New methods must be developed. A group of researchers in Australia have demonstrated a technique for growing ordered polymer nanowires within a pre-patterned electronic circuit such that electrical contacts to the nanowires are made in situ during the growth procedure, avoiding the time-consuming and challenging task of manipulating nanowires into position and making electrical contacts post-synthesis.
Bridges are exciting to cross, incredible works of engineering and they have made it possible for us to travel more easily, quickly and safely. The U.S. Congress even approved $400 million to build a bridge to nowhere. While bridges have been, and still are, essential components in every society's infrastructure, the bridge concept is becoming interesting to nanotechnology researchers as well. Nanomaterial air bridges enable nanoscale structures to be suspended as a two-point beam, creating a nanomechanical element that is isolated from a variety of substrate effects, including adhesion, temperature, conductivity, and parasitic capacitance. The bridge-like suspension makes nanoscale structures accessible along their length, which is beneficial for examining ehmt but also for device construction. It also allows nearfield probing, manipulation, and actuation of these suspended nanostructures. Scientists at the University of Louisville have found a way to build nanomaterial air bridges simply and conveniently.
Transistors are the fundamental building blocks of our everyday modern electronics; they are the tiny switches that process the ones and zeroes that make up our digital world. Transistors control the flow of electricity by switching current on or off and by amplifying electrical signals in the circuitry that governs the operation of our computers, cellular phones, iPods and any other electronic device you can think of. The first transistor used in commercial applications was in the Regency TR-1 transistor radio, which went on sale in 1954 for $49.95, that's over $375 in today's dollars (for everyone in the iPod generation - watch this fascinating 1955 video clip artifact how the first transistor radio was hand built). While the first transistors were over 1 centimeter in diameter, the smallest transistors today are just 30 nanometers thick - three million times smaller. This feat would be equivalent to shrinking the 509-meter tall Taipei 101 Tower, currently the tallest building in the world, to the size of a 1.6 millimeter tall grain of rice. The 32nm microprocessor Intel plans to introduce in 2009 will pack a whopping 1.9 billion transistors. However, current microprocessor technology is quickly approaching a physical barrier. Switching the current by raising and lowering the electron energy barrier generates heat, which becomes a huge problem as device densities approach the atomic limit. An intriguing - and technologically daunting - alternative would be to exploit the wave nature of the electron, rather than its particle properties, to control current flow on the nanoscale. Such a device, called the Quantum Interference Effect Transistor (QuIET), has been proposed by researchers in Arizona. This device could be as small as a single benzene molecule, and would produce much less heat than a conventional field effect transistor.
Back in the early 1800's it was observed that certain chemicals can speed up a chemical reaction - a process that became known as catalysis and that has become the foundation of the modern chemical industry. By some estimates 90% of all commercially produced chemical products involve catalysts at some stage in the process of their manufacture. Catalysis is the acceleration of a chemical reaction by means of a substance, called a catalyst, which is itself not consumed by the overall reaction. The most effective catalysts are usually transition metals or transition metal complexes. An everyday example of catalysis is the catalytic converter in your car which is used to reduce the toxicity of emissions from your car's engine. Here the catalysts are platinum and manganese which for instance convert harmful nitrogen oxides into harmless nitrogen and oxygen. Since catalysts provide a surface for the chemical reaction to take place on, nanoparticles with their extremely large surface area have become much researched as catalysts (as particles get smaller the larger their surface to volume ratio becomes). Especially in heterogeneous catalysis - where the catalyst is in a different phase (ie. solid, liquid and gas) to the reactants, and that is largely influenced by surface properties - use of nanoscale catalysts opens up a number of possibilities of improving catalytic activity and selectivity. Unfortunately, heterogeneous catalysts supported on a carrier prepared using traditional methods (e.g., impregnation) suffer from a number of problems, such as particle aggregation during preparation, sintering during use (especially at high temperatures), and catalyst leaching because of solvent or pressure drop. This is associated with the poor contact of the catalyst particle with the support surface. A new method of catalyst preparation coming out of Singapore may offer a new concept for catalyst optimization.
Just kidding - I always wanted to write a tabloid headline like that! In case you are expecting a story on the mysteries of crop circles caused by alien nanotechnology - stop reading right here; but the analogy is just too striking when you look at the amazing images coming out of the labs at the University of Southern California, where they developed a new technique to create three-dimensional carbon nanotube structures. While carbon nanotubes possess many exceptional properties which far exceed most known bulk materials, creating controlled nanotube (CNT) microstructures has always been a challenge. Overcoming this challenge is going to be key in developing useful and commercially viable CNT devices. Existing techniques for patterning three-dimensional CNT structures are based on the bottom-up growth of multiwalled CNTs (MWCNTs) from a patterned catalyst, which is limited to 2D-like geometries. Other, complex 3D microstructures have been fabricated with polymer-based resin materials but not with CNTs. The new technique developed by researchers in California uses a focused laser beam to selectively burn local regions of a dense forest of MWCNTs. This technique enables chemically sensitive fields to take advantage of nanotubes' exceptional properties and expand their possible applications into new areas.
Lithium-ion (Li-ion) batteries are a type of rechargeable battery commonly used in consumer electronics. They are currently one of the most popular types of battery for portable electronics, with one of the best capacity-to-weight ratios, no memory effect, and a slow loss of charge when not in use. Lithium is useful in batteries because of its lightness (it is the lightest metal) and because of the high voltage of the redox reaction between Li and Li+. In lithium ion batteries, a layered compound - lithium copper oxide or or lithium nickel oxide - is utilized as a cathode. Although this material can provide high capacity, its charging/discharging rates are slow because these processes include the absorption/desorption of lithium in the cathode. Recently, organic radical batteries have been developed as a new type of rechargeable battery, in which organic radical polymers are utilized as a cathode active material. They achieved a very fast chargeable/dischargeable rate, though their capacities are lower than those of the lithium ion batteries. A lot of research has gone into fabricating lithium batteries that achieve both high capacity and fast charging/discharging. Researchers in Japan came up with a completely new idea - the molecular cluster battery - where the cathode active material is a well-known manganese molecular cluster that is stable and insoluble to most solvents and exhibits a multi-step redox reaction. Although the battery was rechargeable, in early experiments the fast charging–discharging was not yet achieved due to the chemical decomposition of the cluster. Nevertheless, this is a first step that opens up a new branch of research into high-performance rechargeable molecular cluster batteries.