Ever since the nanoworld got excited over carbon nanotubes there has been great interest, and progress, in the development of new nanotubes based on metal oxides, sulfides, nitrides, elemental species and others. The characteristic that all these tubular structures have in common is a hollow morphology which may possess circular, or square-like or hexagonal-like cross section. In a standard tubular structure, a cavity is located at the center and extends over the entire length, so that the tube cavity and the tube wall have the same symmetry axis. Structures in which an internal cavity strongly deviates from the center of symmetry towards one side are rather rare. Researchers have now synthesized novel, unconventional nanotubes that are distinctly different from any previously reported nano- and microtubes. These tubes display flattened and thin belt- or ribbon-like morphologies, which are not common for any known tubular structures. This may represent a new, interesting growth phenomenon for tubular crystal structures.
In 1954, Richard Buckminster Fuller was granted U.S. Pat. No. 2,682,235 for geodesic domes, a method of enclosing space in architectural applications. The geodesic dome combines the structural advantages of the sphere (which encloses the most space within the least surface, and is strongest against internal pressure) with those of the tetrahedron (which encloses least space with most surface and has the greatest stiffness against external pressure). Subsequently, soccer ball shaped carbon molecules known as fullerenes or buckyballs were named for their resemblance to a geodesic sphere. But is not only certain carbon molecules where Nature uses sphere-like forms. Spheres can be found at all scales in both the inanimate and living world for the basic physical property of encapsulation. Spherical virus capsids (a capsid is the protein shell of a virus), for example, enclose space by using the geometry of the icosahedron, thus exploiting the economy of this form in terms of both surface area-to-volume ratio and genetic efficiency of subunit-based symmetric assembly. Many viruses' capsids use icosahedral symmetry to form particles ranging from 20 to 200 nanometers in size. Researchers have now begun to copy Nature's icosahedral-symmetry design principles for molecular containers, which could solve the problem of designing and synthesizing stable molecular containers having very large interior.
Looking at Nature as a successful design lab with millions of years of research experience, it is quite surprising that scientists haven't tried harder to copy some of Nature's more successful and impressive design blueprint. The list of actual commercialized biodesign-inspired products is very short. The most famous is Velcro, the hook-loop fastener that was invented in 1945 by Swiss engineer, George de Mestral. The idea came to him after he took a close look at the burrs (seeds) of burdock which kept sticking to his clothes and his dog's fur on their daily summer walks in the Alps. He examined their condition and saw the possibility of binding two materials reversibly in a simple fashion. And then, of course, there are the Wright Brothers, who modeled their planes on the structure of bird wings. Today, there are quite a number of terms such as bionics, biomimetics, biognosis, biomimicry, or even 'bionical creativity engineering' that refer to more or less the same thing: the application of methods and systems found in Nature to the study and design of engineering systems and modern technology. The use of design concepts adapted from Nature is a promising new route to the development of advanced materials and increasingly nanotechnology researchers find nanostructures a useful inspiration for overcoming their design and fabrication challenges. Because biological structures are the result of hundreds of thousands of years of evolution, their designs possess many unique merits that would be difficult to achieve by a complete artificial simulation. However, utilizing them as biotemplates and converting them to inorganic material could be a highly reproducible and low-cost process for fabricating complex nanostructures with unique functions. Complex functional systems are still out of reach but the replication of biological structures is making good progress. A recent example is the fabrication of antireflection nanostructures by replicating fly eyes.
Even the smartest scientists can still learn from the dumbest animals - at least as far as materials science is concerned. Take for instance marine glass sponges such as the hexactinellid sponge Euplectella sp. which are considered to be one of the most primitive animals in existence. Nevertheless, they produce integrated composite materials with outstanding mechanical properties and researchers are interested in finding out how they do that and how this natural process could be copied and adapted for use in the fabrication of synthetic composite materials. Euplectella's bioglass filaments, for instance, exhibit a rather complex design, thus ensuring the control of both mechanical and chemical interfaces between the different components to overcome the brittleness of the main constituent material, glass. Scientists have found that the amazing properties of many biological high-performance materials such as bone or shells are a result of the structure and the interplay of the constituents. In other words, the hierarchical structure of composites determines their material properties, and not the type of the composite's constituents. Researchers in Germany have now reported a biomimetic approach for the fast fabrication of hierarchically structured peptide-silica fibers, mimicking the bio-silicification process of natural glass fibers.
As a critical component of optoelectronic devices, transparent conductive coatings pervade modern technology. The most widely used standard coating is indium tin oxide (ITO), used in nearly all flat panel displays and microdisplays. Causing problems for manufacturers, though, Indium is expensive and scarce and demand is increasing. From the depressed levels of $60/kg in 2002, indium prices rose to over $1,000/kg during the summer of this year. Recently, prices have fallen back to between $400-$500/kg. But, geologists say the cost of indium may not matter soon, because the earth's supply of this element could be gone within just a few years. In addition to the limited availability of Indium there are other reasons that make ITO and other metal oxides such as FTO (fluorine tin oxide) increasingly problematic for electronics manufacturers: the instability of these metal oxides in the presence of acid or base; their susceptibility to ion diffusion into polymer layers; their limited transparency in the near-infrared region; and lastly, the current leakage of FTO devices caused by FTO structure defects. This has made the search for novel transparent electrode materials with good stability, high transparency and excellent conductivity a crucial goal for optoelectronic researchers. Recent work by researchers in Germany exploits ultra-thin transparent conductive graphene films as window electrodes in solar cells.
Past studies of photo-responsive proteins have generally dwelled on applications for energy-saving computer displays, light-based computing or computer memory. The general theme in the research tends to rely on the controllable and quick state change of the protein. But, the ability of the protein to actually incite a physical change in a composite macroscopic system has been largely unexplored. Harnessing this ability of the protein to incite change in a polymeric material could have broad implications in the field of biomedical and materials engineering. Getting bacteriorhodopsin to 'play ball' with other bulk materials could render those materials sensitive to a light. As a stimulus, light is often much easier to control than those typically explored by researchers such as bulk pH, temperature or electric fields.
The Bronze Age technique of soldering - a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint - seems to be working just fine in the nanotechnology age. Researchers in California have developed an alternative method, effectively a miniaturization of soldering, to electron beam lithography (EBL) which, so far, is the method of choice for making electrical contact to nanostructures is. Carbon nanotubes, for instance, have been soldered together by using electron beam deposited gold molecules. There is a downside to using EBL as an industrial fabrication process: commercially used dedicated e-beam writing systems are very expensive (millions of dollars per unit), the process is complex, time-consuming and not really suitable for high-volume manufacturing, and there is a risk of sample contamination build-up on the samples. Other lithography-free contacting techniques such as shadow masks have been attempted, but they have their own drawbacks and have not been widely used. The new nano-soldering technique allows to make submicron sized, Ohmic contacts to nanostructures of even single atom thickness. The technique is simple, inexpensive, rapid, and entirely avoids sample contamination.
Machines usually require various components such as bearings, gears, couplings or pistons. As machines shrink to the micro- and ultimately nanoscale, their components of course need to shrink with them. One of the major obstacles to the realization of intricate nanomachines like nanorobots is the lack of effective processes for building freestanding nanocomponents with specific shapes and sizes. Self-assembly methods produce both organic and inorganic nano-objects with high yields through 'bottom-up' approaches. The shapes, however, in most cases are confined to rather simple forms such as spheres, rods, triangles and cubes etc. and are not suitable for the elementary components of intricate nanomachines. Meanwhile, the 'top-down' approaches including electron beam lithography and micro-contact printing etc. focus on surface patterning or fabrication of suspended objects, although they can fabricate sophisticated nanostructures. So far, the fabrication and assembly of nano-objects with specific shapes and sizes that can act as elementary components for movable nanoelectromechanical systems (NEMS) is only at the conceptual stage. New research results coming from South Korea now offer the first step toward the realization of sophisticated nanomachines, designed to perform specific tasks, with overall dimensions comparable to those of biological cells.