The success of the semiconductor industry has been due in large part to its ability to continuously increase the complexity, and therefore the processing power, of integrated circuits at a given manufacturing cost. Moore?s Law observes that the number of transistors in a computer chip doubles every two years, whilst the cost of making the chip remains the same, due to miniaturization of the components. In order to produce the next generation of computer chips it is necessary to continue to shrink the size of the components on the chip. The miniaturization upon which Moore?s Law rests has been achieved through advances in the photolithographic process used to pattern the components onto to the silicon wafer. A beam of light is projected through a shadow-casting reticule and the light pattern is then directed onto a silicon wafer coated with a photochemically sensitive material, known as a resist. The solubility of the resist is modified by exposure to the light, allowing specific areas of the resist film to be removed, whilst other areas remain as a mask, so that the silicon wafer can be selectively etched, metallized or doped. For many years it has been predicted that the end of photolithography is approaching, and that further miniaturization will require next generation lithography techniques, such as EUV lithography. However, photolithography has proved remarkably resilient, and continues to improve. Unfortunately, whilst the ability of photolithography to pattern small features continues to improve, the industry is beginning to challenge the capabilities of the photosensitive resist.
One of the best ways to gain control over synthesis of nanoparticles is to watch it happen. Take carbon nanotubes (CNTs): Synthesis of CNTs is a field that is growing explosively - but there is a lot that nanotechnology researchers don't know about how nanotubes form and grow. While there are a number of in situ characterization methods for nanotube synthesis under development worldwide, each with different strengths and weaknesses, much of the information about the nanotube structure is indirect.
Historically, in situ characterization tools have accelerated progress in synthesis for many advanced materials, and there is widespread recognition that in situ tools have the potential to improve CNT synthesis as well. Ideally one would like to detect individual nanotubes and ensembles as they grow and measure their physical properties while imposing minimal constraints on the synthesis method. In other words, with a good understanding of the synthesis process we would be better able to control the product.
Transparent conductive coatings pervade modern technology and they are a critical component of optoelectronic devices. Today, the most widely used standard coating in nearly all flat panel displays and microdisplays is indium tin oxide. As indium becomes increasingly scarce and expensive, the search for novel transparent electrode materials with good stability, high transparency and excellent conductivity has become a crucial goal for optoelectronic researchers. There are strong and successful efforts from several research groups around the world to develop optoelectronic devices on the basis of individual single-walled carbon nanotubes. This development is of great scientific interest, although there are major challenges in finding technologically feasible ways to assemble the individual nanotube devices into functioning electronic circuits with a high level of integration.
Having come a long way from pottery and tableware, modern advanced ceramics are high-performance materials that find use in things such as bio-medical implants, jet engine turbine blades, superconductors, missile nose cones, scratch-proof watches, or the heat protection tiles used on the Space Shuttle. Super-tough and ultra-high temperature resistant materials are in critical need for applications under extreme conditions such as jet engines, power turbines, catalytic heat exchangers, military armors, aircrafts, and spacecrafts. Structural ceramics have largely failed to fulfill their promise of revolutionizing engines with strong materials that withstand very high temperature. The major problem with the use of ceramics as structural materials is their brittleness. Although many attempts have been made to increase their toughness, including incorporation of fibers and particles, currently available ceramics and their composites are still not as tough as metals and polymers. The brittleness of ceramic materials has not yet been overcome and it has proven difficult to solve this problem by conventional material engineering approaches. The extraordinary mechanical properties of carbon nanotubes (CNTs) have generated strong research interest in their possible use in reinforced composite materials because incorporating CNTs into a ceramic matrix might be expected to produce tough as well as highly stiff and thermostable ceramic composites.
The use of spontaneous self-assembly as a lithography- and external field-free means to construct well-ordered, often intriguing structures has received much attention for its ease of organizing materials on the nanoscale into ordered structures and producing complex, large-scale structures with small feature sizes. These self-organized structures promise new opportunities for developing miniaturized optical, electronic, optoelectronic, and magnetic devices. An extremely simple route to intriguing structures is the evaporation-induced self-assembly of polymers and nanoparticles from a droplet on a solid substrate. However, flow instabilities within the evaporating droplet often result in non-equilibrium and irregular dissipative structures, e.g., randomly organized convection patterns, stochastically distributed multi-rings, etc. Therefore, fully utilizing evaporation as a simple tool for creating well-ordered structures with numerous technological applications requires precise control over several factors, including evaporative flux, solution concentration, and the interfacial interaction between solute and substrate.
Electrometers are instruments that measure electric charge or electrical potential difference by means of electrostatic force. While early electrometers such as developed by Lord Kelvin in the 19th century were crude instruments, modern electrometers based on solid state technology are high-precision electronic devices that, in extreme cases, are so sensitive they can count individual electrons as they pass through a circuit. As the dimensions of electronic devices shrink further, the probes required to measure the voltage inside a miniature conductor have to be miniaturized, too. An alligator clip cannot be scaled down indefinitely to perform such tasks. Furthermore, as devices reach the nanoscale, the perturbation of the measurement on the device itself cannot be neglected and must be assessed. A few techniques, many of which are based on scanning a small object such as an atomic force microscope (AFM) tip, have been developed in the past to address this challenge. Each technique has its pros and cons.
Various techniques are being developed to enhance the already impressive properties of carbon nanotubes (CNTs) further by combining them with other materials. We have covered plenty of examples in our Spotlights. For instance, encapsulating carbon nanofibers with CNTs transforms cheap commercial carbon nanotubes into highly efficient carbon for electrochemical energy storage applications. Another study demonstrated that the redox properties of iron and iron oxide particles are tunable via encapsulation within CNTs, suggesting that a host-guest interaction between the confined metal particles and CNTs, which is different from that on the outside of the nanotubes. Researchers are still busy trying to understand some of the CNT basics, for instance something as fundamental as 'how do nanotubes grow'? How can their various properties - electronic, transport, or mechanical - be modified? Or how can you make use of CNT's structure and properties to build novel nanotools. A new model demonstrates that sufficiently small liquid metal droplets can be drawn inside a CNT via capillary action.
Scientists consider the exploration of carbon nanotubes (CNTs) for biomedical applications as a field with significant potential, leading to applications where CNTs could act as magnetic nano-heaters, drug-carrier systems and sensors which allow a diagnostic and therapeutic usage on a cellular level. The EU, for instance, has funded a four-year nanotechnology research program that studies the chemical and physical properties of CNTs in order to find mechanisms which can be applied for a biomedical purpose in appropriate medical devices. Studies of their interaction with biological environments (immune response, toxicity, interaction with the single cell) will provide the basis for applying the CNT for imaging (nanoparticles-based contrast agents), sensoring (nanoparticles-based diagnostics) and cancer treatment (hyperthermia, nanotechnology-based targeted drug delivery). A new study that exploits the unique properties of single-walled CNTs (SWCNT) for biomedical purposes shows the use of SWCNTs as an efficient platform for immunotherapeutic applications. Scientists demonstrate the surface area tunability of SWCNT bundles by chemical treatment and its effect on antibody adsorption and subsequent T cell activation. T cells are central players in initiating and maintaining immune responses. An important goal of successful immunotherapy is the stimulation of T cell immune responses against targets of interest such as tumors.