Sophisticated optical lithography techniques have been developed by the semiconductor industry to pack more and more transistors onto chips. On the road to a billion transistors per chip, Intel has already developed transistors so small that 200 million of them could fit on the head of a pin. As if that wasn't small enough, scientists are pushing further down, hoping to be able one day to reliably (and affordably) control surface features as small as 1 nm. With today's technology, cost-effective fabrication in the sub-50 nm range is a major challenge. Given the advanced development of (nano)lithography it is not surprising that various forms of it are the most common techniques used by nanotechnology researchers for manipulating sub-100 nm surface features. With the current state of optical lithography it appears that traditional commercial lithography techniques will not be cost effective below 30 nm. State-of-the-art electron beam lithography (EBL) has been proved to be capable of delivering resolution in the 10 nm range. Unfortunately, EBL is slow, very expensive and it is very unlikely that it can effectively go below 10 nm. The same limitations hold for x-rays and focused ion beams (FIBs), with additional tremendous difficulties in developing equipment for beam manipulation and focusing on nanometer scales.
Nature has excelled in designing molecular motors, something nanotechnology researchers are still having a hard time with. The potential for nano-actuators (a nanoscale device that creates automatic motion by converting various forms of energy to rotary or linear mechanical energy) is huge - basically any active system that performs some kind of work requires an energy source. Applications reach from simple pumps on lab-on-a-chip devices to move nanoliters of fluid around to nanoscale motors for nanorobotic systems. One of the challenges of designing such a motor for the nano realm is that during the design of a nano-actuator the tradeoffs among range of motion, force, speed (actuation frequency), power consumption, control accuracy, system reliability, robustness, load capacity, etc. must be taken into consideration. Most microscale systems are currently achieved by relatively large external actuators such as syringe pumps, or high voltage power supplies, which negates the advantages of the microfabricated systems. That's why scientists are quite intrigued by the opportunity to use biological organisms to construct mechanical actuators in engineered systems at the micro- or even nanoscale. An extremely powerful biological motor is the bacterial flagellar motor found in organisms such as Escherichia coli or Serratia marcescens. Bacteria draw chemical energy directly from their environment and are able to survive in a wide range of temperature and pH. What makes bacterial propulsion system interesting for nanotechnology researchers is that bacteria are exquisitely sensitive to a wide variety of external stimuli. So far, scientists have managed to control them en masse through light (phototaxis) and chemical (chemotaxis) sensory mechanisms. In a recent example of successful use of live bacteria as mechanical actuators, scientists have built a microfluidic pump powered by self-organizing bacteria.
One statement of the second law of thermodynamics is that the efficiency of any heat engine or other thermodynamic process is always less that 100%. There will always be some type of friction or other inefficiency that will generate waste heat. The useful work that a heat engine can perform will therefore always be less than the energy put into the system. Engines must be cooled, as a radiator cools a car engine, because they generate waste heat. While there is no way around the second law of thermodynamics, the performance of today's power generation technology is quite appalling. The average efficiency today for fossil-fired power generation, 35% for coal, 45% for natural gas and 38% for oil-fired power generation. By the way, be skeptical when people tell you that nuclear power is good in the fight against global warming - nuclear power plants have a worse thermal efficiency (30-33%) than fossil-fired plants. Approximately 90% of the world's power is generated in such a highly inefficient way. In other words: every year some 15 billion kilowatts of heat is dumped into the atmosphere during power generation (talk about fueling global warming...). This is roughly the same amount as the total power consumption of the world in 2004. Reducing these inefficiencies would go a long way in solving the coming energy and climate problems. Thermoelectric materials - which can directly convert heat into electricity - could potentially convert part of this low-grade waste heat. Problem is that good thermoelectric materials are scarce and so far solid-state heat pumps have proven too inefficient to be practical. Two papers in this week's Nature describe how silicon devices could in principle be adapted and possibly scaled up for this purpose.
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.