In its everlasting quest to deliver more data faster and on smaller components, the silicon industry is moving full steam ahead towards its final frontiers of size, device integration and complexity. We have covered this issue numerous times in previous Spotlights. As the physical limitations of metallic interconnects begin to threaten the semiconductor industry's future, one group of researchers and companies is betting heavily on advances in photonics that will lead to combining existing silicon infrastructure with optical communications technology, and a merger of electronics and photonics into one integrated dual-functional device. Today, silicon underpins nearly all microelectronics but the end of the road for this technology has clearly come into view. Photonics is the technology of signal processing, transmission and detection where the signal is carried by photons (light) and it is already heavily used in photonic devices such as lasers, waveguides or optical fibers. Optical technology has always suffered from its reputation for being an expensive solution, due to its use of exotic materials and expensive manufacturing processes. This prompted research into using more common materials, such as silicon, for the fabrication of photonic components, hence the name silicon photonics. Although fiber-optic communication is a well-established technology for information transmission, the challenge for silicon photonics is to manufacture low-cost information processing components. Rather than building an entirely new industrial infrastructure from scratch, the goal here is to to develop silicon photonic devices manufactured using standard CMOS techniques. A recent review paper takes a look at the state of silicon photonics and identifies the challenges that remain on the path to commercialization.
You have seen the effect: if you splash water on your car it leaves wet areas; if you do this with your freshly polished car the drops just pearl off. Materials scientists are very interested in designing surfaces that allow them to control this effect - called wetting - because it enables them to fabricate things like more comfortable contact lenses, better prosthetics, and self-cleaning materials. The primary measurement to determine wettability is the angle between the solid surface and the surface of a liquid droplet on the solid's surface. For example, a droplet of water on a hydrophobic surface would have a high contact angle, but a liquid spread out on a hydrophilic surface would have a small one. Maintaining the position of a drop of water on a hydrophobic surface (e.g. your newly waxed car) appears to be impossible - it will just move across the surface. Scientists in Israel have managed to fabricate a nanostructured, highly hydrophobic surface that allows them to pin a nearly spherical drop of water in place. A droplet sitting on one class of these substrates did not fall even after the substrate was turned upside-down! An important application for this novel fabrication technique could be as a tool in single-molecule spectroscopy: a water drop, containing molecules to be probed, could be pinned down for an extended time, allowing to spectroscopically probe it for long periods without affecting the properties of molecules, or even just one molecule, dissolved in the water drop.
Notwithstanding the mixed news (to put it mildly) that individual investors have been getting from their nanotechnology stock portfolios, industry as a whole is pressing ahead with incorporating nanotechnologies in their products and processes. Unlike many other areas of science, nanosciences are capable of influencing a wide sweep of industrial and medical processes, from cleaner energy applications, to smart materials and revolutionary medical applications. It is increasingly difficult to know which products use nanotechnology or incorporate nanomaterials; nanotechnology consumer product directories give an idea where nanomaterials are used but are increasingly useless in helping to understand the full extent of nanotechnologies penetrating industrial manufacturing processes. Some consumer companies embrace 'nano' wholeheartedly and advertise their 'revolutionary' face creams, tennis rackets and car waxes; some, after increased scrutiny, have become very quiet about their nanotechnology activities (especially the large cosmetics and food companies); and some even change their company name to something that doesn't include 'nano' ('cleantech' or 'greentech' has become the new nanotech). Combine this technological shift that is taking place in industries across the board with the still existing lack of conclusive answers about the toxicity of nanomaterials, and you get a worrisome mix of industry pushing ahead unconstrained, a regulatory environment where key constituencies are ill prepared and underfunded to address the issues with the speed required, and public opinion that covers the whole range from activists calling for a complete moratorium on all things nano to snake-oil salesmen who promise nanotechnology stock tips that will make you a gazillionaire. Oh, and apparently now you can also add to this mix certain religious types in the U.S. who find nanotechnology is morally not acceptable.
A new study reveals that nanoparticles do not just act as simple, passive carriers but are actively involved in mediating biological activity. These findings have significant implications in understanding the interactions of nanostructures with biological systems. But, once properly understood, they could be important in assisting in the design of intelligent nanodevices, with great potential for the development of novel molecular-based diagnostics and therapeutics. On the other hand, they could also be useful in understanding nanotoxicity. In spite of what has been achieved so far by scientists and clinical researchers, a complete understanding of how cells interact with nanostructures of well-defined sizes, at the molecular level, remains poorly understood.
Whenever you read an article about nano this or nano that, chances are you come across a large number of confusing three-letter acronyms - AFM, SFM, SEM, TEM, SPM, FIB, CNT and so on. It seems scientists earn extra kudos when they come up with a new three-letter combination. One of the most important acronyms in nanotechnology is AFM - Atomic Force Microscopy. This instrument has become the most widely used tool for imaging, measuring and manipulating matter at the nanoscale and in turn has inspired a variety of other scanning probe techniques. Originally the AFM was used to image the topography of surfaces, but by modifying the tip it is possible to measure other quantities (for example, electric and magnetic properties, chemical potentials, friction and so on), and also to perform various types of spectroscopy and analysis. Today we take a look at one of the instruments that has it all made possible. So far, over 20,000 AFM-related papers have been published; over 500 patents were issued related to various forms of scanning probe microscopes (SPM); several dozen companies are involved in manufacturing SPM and related instruments, with an annual worldwide turnover of $250-300 million, and approx. 10,000 commercial systems sold (not counting a significant number of home-built systems).
'Field evaporation' is the phenomenon by which surface atoms are ionized (evaporated) under an applied, extremely high electric field of the order of several volts per nanometer. Electric fields of this magnitude can only be achieved by applying a high field to an extremely sharp needle such as the specimen tip in a Field Ion Microscope. Field evaporation was first reported over 50 years ago and has since developed into the powerful Atom Probe Field Ion Microscopy which is able to reproduce the atomic structure of a piece of material in three dimensions. Today, field evaporation is mainly used for material characterization, and the behavior of nanomaterials at extremely strong electric fields is of great scientific and technological interest. In principle, the field evaporation phenomenon can be utilized not only for materials characterization, but also for materials processing and morphology control with extremely high precision because of its unique atom-by-atom removal capability. However, detailed structural evolution of nanomaterials during field evaporation has never been directly observed and this limitation has greatly restricted the potential applications of field evaporation as a materials-processing tool. Now, researchers in Beijing have reported the first direct observation of field evaporation phenomena using a transmission electron microscopy (TEM) technique. By conducting in situ TEM field evaporation experiments on individual carbon nanotubes (CNTs), the researchers were able to reveal details about the structural evolution of the nanomaterials via direct observation. Using this technique, they have been able to perform controlled engineering of the CNTs with atomic precision, for example, grinding and shortening of CNTs, shaping of the open ends of CNTs, and opening of CNT caps.
Harnessing the power of the sun to replace the use of fossil fuels holds tremendous promise. One way to do this is through the use of solar, or photovoltaic, cells. Large-scale installation already show the technical feasibility of this technology although the major problem of photovoltaic solar energy - its relative inefficiency - still needs to be overcome to make the cost of electricity produced by solar cells equal or less than electricity produced by nuclear or fossil fuels. Until now, solar cells that convert sunlight to electric power have been dominated by solid state junction devices, often made of silicon wafers. Efforts are being made in laboratories worldwide to design ordered assemblies of semiconductor nanostructures, metal nanoparticles and carbon nanotubes for constructing next generation solar energy conversion devices. Quantum dots have been identified as important light harvesting material for building highly efficient solar cells. Quantum dots are nanoscale semiconductor structures which, when exposed to light at certain wavelengths, can generate free electrons and create an electrical current. Quantum dot technology represents an exciting field of research in solar energy yet the actual research results to use them in solar cells are relatively limited. By combining spectroscopic and photoelectrochemical techniques, researchers now have demonstrated size-dependent charge injection from different-sized cadmium selenide (CdSe) quantum dots into titanium dioxide nanoparticles and nanotubes, showing a way to maximize the light absorption of quantum dot-based solar cells. Termed 'rainbow solar cells', these next-generation solar cells consist of different size quantum dots assembled in an orderly fashion. Just as a rainbow displays multiple colors of the visible light spectrum, the 'rainbow solar cell' has the potential to simultaneously absorb multiple wavelengths of light and convert it to electricity in a very efficient manner.
Years of engineering research and design, together with uncounted billions of dollars from government and industry, went into the development of the modern petroleum industry. It would be unreasonable to expect that we can replace this industry with greener alternatives without a similarly expansive and sustained effort. Point in case is a recently published roadmap to 'Next Generation Hydrocarbon Biorefineries' that outlines a number of novel process pathways for biofuels production based on scientific and engineering proofs of concept demonstrated in laboratories around the world. The key conclusion from this (U.S.-centric) report is that 'while the U.S. has made a significant investment in technologies focusing on breaking the biological barriers to biofuels, principally ethanol, there has not been a commensurate investment in the research needed to break the chemical and engineering barriers to hydrocarbon fuels such as gasoline, diesel, and jet fuel.' This statement of course holds true not only for biofuels but for any kind of green energy technology. The production of ethanol from corn has come under intense scrutiny and discussion for its potential environmental and economic side effects. Advances in agriculture and biotechnology have made it possible to inexpensively produce lignocellulosic biomass (plant biomass that is composed of cellulose and lignin) at costs that are significantly lower (about $15 per barrel of oil energy equivalent) than crude oil. The key bottleneck for lignocellulosic-derived biofuels is the lack of technology for the efficient conversion of biomass into liquid fuels. Advances in nanotechnology have given us an unprecedented ability to understand and control chemistry at the molecular scale, which promises to accelerate the development of biomass-to-fuels production technologies.