Antireflection coatings have become one of the key issues for mass production of silicon solar cells. Silicon solar cells are the most common solar cells on the market today. They are constructed with layers of n-type silicon having many electrons and p-type silicon having many electron holes. When hit by sunlight, an equal number of electrons and electron holes are generated at the interface between the two silicon layers and, as the electrons migrate from the n-type silicon to the p-type silicon, an electric flow is generated. One of the problems with silicon solar cells is the high refractive index of silicon, which causes more than 30% of incident light to be reflected back from the surface of the silicon crystals. Solar cell manufacturers have therefore developed various kinds of antireflection coatings (ARCs) to reduce the unwanted reflective losses. Currently, quarter-wavelength silicon nitride thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) are the industrial standard for ARCs on crystalline silicon substrates. Unfortunately, current top-down lithographic techniques for creating subwavelength silicon gratings, such as electron-beam lithography, nanoimprint lithography, and interference lithography, require sophisticated equipment and are expensive to implement, thus contributing to the still high costs of this type of solar cells. Borrowing from Mother Nature's millions of years old design book, researchers have now come up with a nanotechnology antireflection coating inspired by the eyes of moths.
A major issue for using self-contained nanodevices, for instance as implantable nanosensors or environmental monitoring devices, is the question of how to power these tiny machines with an independent power source. Options include nanobatteries and nanogenerators that harvest energy from their environment. By converting mechanical energy from body movement, engine vibrations, or water or air flow into electricity, these nanoscale power plants could make possible a new class of self-powered medical devices, sensors and portable electronics. Probably the leading team that is driving forward the work on nanogenerators for converting mechanical energy into electricity is Zhong Lin Wang's group at Georgia Tech. Wang's team has now designed and demonstrated an innovative approach to fabricating a nanogenerator by integrating nanowires and pyramid-shaped nanobrushes into a multilayer power generator. By demonstrating an effective way for raising the output current, voltage and power, this work provides the technological platform for scaling up the performance of nanogenerators to a level that some day might be able to independently power devices like pacemakers or iPods.
Nanoscale membranes are of great interest to researchers not only for nanofiltration applications but also in areas such as flexible electronics, extremely sensitive sensors, nanomedical applications and biomolecular research. Many of these applications would require the nanomembranes to be arranged in three-dimensional structures such as tubes, helices, rings, or wrinkles. So far, the roll-up of ultra-thin layers was heavily limited in materials choice, in most cases involving epitaxial semiconductor layers. The fabrication often requires a selective underetching procedure to release the nanomembranes from their substrate, a process which not only removes the underlying sacrificial layer but also in many cases dissolves the nanomembrane material itself. A new approach developed by scientists in Germany and Hong Kong now allows controlled fabrication of pure metal and oxide tubes as well as many other material combinations. They describe a general method to produce well-defined micro- and nanotubes from thin solid films deposited by mass production tools.
The long-term vision of revolutionary bottom-up nanotechnology is based on two different concepts of molecular assembly technologies. One follows Nature's blueprint, which uses molecular recognition for self-assembly of nanoscale materials and structures; the other is man-made and uses instruments to assemble nanoscale building blocs into larger structures and devices. In contrast, the most common nanoscale fabrication techniques used today, for instance in the sub 100-nanometer semiconductor industry, are top-down approaches where fabrication technologies such as lithography or stamping are used. Here, you create ever smaller structures by starting with a block of material and remove the bits and pieces you don't want until you get the shape and size you do want. While top-down techniques can be highly parallel (semiconductor industry) it is not feasible to control single molecules with them. Using a hybrid approach that combines the precision of an atomic force microscope with the selectivity of DNA interactions, researchers in Germany have successfully demonstrated a technique that fills the gap between top-down and bottom-up since it allows for the control of single molecules with the precision of atomic force microscopy and combines it with the selectivity of self-assembly.
Our Spotlight today again shows an example of the very fundamental research that is taking place in labs around the world to lay the foundation for future nanotechnology based devices. It illustrates the very early stage of development and the nature of the fundamental challenges that make up today's 'nanotechnology research. The vision of revolutionary bottom-up nanotechnology is based on a concept of molecular assembly technologies where nanoscale materials and structures self-assemble to microscale structures and finally to macroscopic devices and products. Researchers are a long, long way from realizing this vision but they are busily laying the foundation for nanoscale engineering. Assembling nanoscopic components into macroscopic materials is 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. Right now, nanotechnology researchers have their hands full just learning how to control a straight chain of nanoparticles.
Using nanoparticles to combat cancer and a host of other diseases is an active area of research for many scientists. For decades, treating cancer has mostly involved injecting patients with toxic drugs. A practice, in which only a fraction of the drugs reach the intended target, killing healthy cells in the process and causing harmful side effects. Previous studies have shown that drug-carrying nanoparticles can accumulate in and attack tumors, in part because of their extremely small size, which helps allow them to pass through cell membranes. However, up until now, existing techniques have meant that targeting agents could only be delivered using spherical or granular shaped particles. Now, a team of scientists have demonstrated that nanoparticles designed with a specific shape, size and surface chemistry are taken up into cells and behave differently within cells depending on the characteristics of the particle.
The demand for the raw materials of the nanotechnology revolution - nanoparticles, carbon nanotubes, fullerenes, quantum dots, etc - is rising explosively and large chemical companies keep expanding their production capacities. These industrial scale systems often depend on precious input materials and energy-hogging processes. However, there are vast amounts of 'useless' natural materials literally lying around - rocks and stones - which could find their way into nanotechnology.Researchers in Germany have made a proof of concept demonstration that using natural nanostructures found in lava rocks is suitable for nanomaterial synthesis and for use in catalysis for production of butadiene and styrene.
The motor proteins of the cytoskeleton accomplish nanotransport tasks by moving 'cargo' along microtubules that are about 25 nm wide but can grow up to 1,000 times as long. Nanotechnology engineers are fascinated by this transport mechanism and several efforts are underway in various labs to unravel and, researchers hope, eventually copy nature's engineering feat. A particularly promising setup consists of surface-attached linear motor proteins that drive the motion of cytoskeletal filaments. Some researchers expect that artificial molecular transport systems which utilize microtubules motility will be an alternative to pressure-driven or electrokinetic flow-based microfluidic devices. Researchers in Germany describe a novel method to characterize the rotational movement of cytoskeletal filaments gliding over motor-coated substrate surfaces. This technique allows exploring the detailed paths that motors take on cytoskeletal filaments. This is also important in understanding situations of heavy intracellular traffic, where motors might have to switch lanes.