Large-scale and high-density semiconductor arrays with one-dimensional ("1D" - where one dimension of the structure is nanoscale) nanostructures have been extensively studied for their potential application in future electrooptical devices. Among them, zinc oxide (ZnO) is considered to be very attractive for high-efficiency short-wavelength optoelectronic nanodevices because of its large exciton binding energy of 60 meV and high mechanical and thermal stabilities. ZnO nanorod/ nanowire arrays have also been demonstrated to be highly versatile and proven to be quite effective in piezoelectric nanogenerators, dye-sensitized solar cells, photonic crystals, superhydrophobic surfaces, and even biodevices due to their biocompatibility. One of the issues researchers are still grappling with is the synthesis of ZnO nanowire arrays. On one hand, high-temperature techniques such as chemical vapor deposition (CVD) have been widely employed and result in high quality nanostructures. However, these methods are energy-consuming and expensive. On the other hand, there are several advantages of growing semiconducting nanostructures directly on conducting metal substrates, for instance the formation of robust electrical contacts during the growth. Such wet chemical methods, which are appealing for their low temperature, facile manipulation, and potential for scale-up have recently been developed for the production of aligned ZnO nanostructures and so far the most successful route has been seeded growth on ZnO-nanoparticle-coated substrates. In these two-step processes the coating of the substrate for the formation of a nucleation layer remains complex and difficult/irreproducible. Therefore, large-scale, low-cost controllable growth of well-aligned ZnO 1D nanostructures on properly fitting substrates via a one-step synthetic approach is still crucially needed for novel applications to become practicable. Researchers in China now have demonstrated exactly such a highly effective solution by growing well-aligned ZnO 1D nanostructures on various inert metal substrates at low temperature on a large scale.
Thin, flexible displays have become an everyday component in many electronic gadgets from cell phones to digital cameras and MP3 players. Most of these displays are based on LCD technology, liquid crystals combined with polymeric structures, and one of their drawbacks is that their manufacturing cost grows rapidly with increasing screen size. A recently developed alternative approach for thin, flexible displays makes use of thermochromic composite thin-films. Thermo- chromism is the ability of a substance to change color due to a change in temperature. This first of a kind thermochromic display is based on films with thermochromic nanoparticles and embedded conductive wiring patterns. Based on the ease of fabrication and simple architecture, thermochromic displays could have advantages in lowering the display unit cost and, due to their heating pulse control scheme, can also lower power consumption compared with conventional displays.
You cut yourself in the finger - and a few days later your skin has completely healed again. Biological organisms have an amazing ability to automatically initiate self-healing and self-repair when they sustain damage. Materials engineers are dreaming about making materials that could do the same thing. Imagine self-repairing cars, planes, bridges or buildings. These materials could be of particular use in structures that are at present impractical or impossible to repair, such as electronic circuit boards, implanted medical devices or spacecraft. Self-repairing materials would have a massive impact on virtually all industries, lengthening product lifetimes, increasing safety, and lowering product costs by reducing maintenance requirements. Thanks to nanotechnology, these visions are coming closer to reality. One approach is the use of nanocontainers that possess the ability to release encapsulated active materials in a controlled way, leading to a new family of self-repairing coatings.
OLEDs - organic light-emitting diodes - are full of promise for a range of practical applications not too far into the future. Today, OLEDs are used in small electronic device displays in mobile phones, MP3 players, digital cameras, etc. With more efficient and cheaper OLED technologies we soon will see ultraflat, very bright and power-saving OLED televisions, windows that could be used as light source at night, and large-scale organic solar cells. In contrast to regular LEDs, the emissive electroluminescent layer of an OLED consists of a thin-film of organic compounds. What makes OLEDs so attractive is that they do not require a backlight to function. Thus they draw far less power and, when powered from a battery, can operate longer on the same charge. OLED devices can be made thinner and lighter than comparable LED devices. Last but not least, OLEDs can be printed onto almost any substrate with inkjet printer technology, making new applications like displays embedded in clothes or roll-up displays possible. Unfortunately there are also drawbacks to this technology. Apart from its currently high manufacturing cost, the major problem is device degradation and the limited lifetime of organic materials. In particular, the most commonly used material for the anode, ITO (indium tin oxide), is a less than optimal material for future high-performance OLEDs. New research indicates that nanoimprinted semitransparent metal electrodes, replacing ITO electrodes, are an attractive and potentially practical solution for OLEDs and other organic devices.
One of the most common methods of film manufacture is Blown Film Extrusion. The process, by which most commodity and specialized plastic films are made for the packaging industry, involves extrusion of a plastic through a circular die, followed by "bubble-like" expansion. The resulting thin tubular film can be used directly, or slit to form a flat film. Nanoscientists now have found a way to use this very common and efficient industrial technology to potentially solve the problem of fabricating large-area nanocomposite films. Currently, the problems with making thin film assemblies are either the production cost of using complex techniques like wet spinning or the unsatisfactory results of unevenly distributed and lumping nanoparticles within the film. The new bubble film technique results in well-aligned and controlled-density nanowire and carbon nanotubes (CNTs) films over large areas. These findings could finally open the door to affordable and reliable large-scale assembly of nanostructures.
In 2005, researchers in the Netherlands developed the concept of a "molecular printboard" (named for its parallels with a computer motherboard) - a monolayer of host molecules on a solid substrate on which guest molecules can be attached with control over position, binding strength, and binding dynamics. Molecules can be positioned on the printboard using supramolecular contact printing and supramolecular dip-pen nanolithography. In this way, nanoscale patterns can be written and erased on the printboard. This technique, which combines top-down fabrication (lithography) with bottom-up methods (self-assembly), has now been applied to proteins. The resulting "protein printboards", allowing the capture and immobilization of proteins with precise control over specificity, strength and orientation, allows the fabrication of protein chips for applications in proteomics. They will play a major role in unraveling the human protein map, just as special chips were instrumental in mapping human DNA.
Nanofluidic channels, confining and transporting tiny amounts of fluid, are the pipelines that make the cellular activities of organisms possible. For instance, nanoscale channels carry nutrients into cells and waste from cells. Researchers are trying to mimic Nature by constructing nanochannels in order to be able to manipulate single molecules in, predominantly biomedical, applications. Although nanochannels adjustable in size are prevalent in Nature, it is challenging to fabricate them artificially because of conflicting requirements for rigid structural integrity (to prevent collapse) on one hand and reconfigurability of nanometer-sized features on the other (to allow adjustability). Recent work at the University of Michigan addresses these issues and introduces methods to rapidly prototype structurally stable yet reconfigurable nanochannels. By fabricating tuneable elastomeric nanochannels for nanofluidic manipulation, the researchers were able to properly balance the need for flexibility and rigidity.
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.