Single-walled Carbon Nanotubes (SWNTs) are nanometer-diameter cylinders consisting of a single graphene sheet wrapped up to form a tube. Since their discovery in the early 1990s[1, 2], there has been intense activity exploring the electrical properties of these systems and their potential applications in electronics. Experiments and theory have shown that these tubes can be either metals or semiconductors, and their electrical properties can rival, or even exceed, the best metals or semiconductors known. Particularly illuminating have been electrical studies of individual nanotubes and nanotube ropes (small bundles of individual nantoubes). The first studies on metallic tubes were done in 1997[3, 4] and the first on semiconducting tubes in 1998[5]. In the intervening five years, a large number of groups have constructed and measured nanotube devices, and most major universities and industrial laboratories now have at least one group studying their properties. These electrical properties are the subject of this review. The data presented here are taken entirely from work performed by the authors (in collaboration with other researchers), but they can be viewed as representative of the field.
Like the California gold rush of 1849, the emergence of nanotechnology presents both an enormous opportunity and enormous risks. Just as new techniques, rewards, and challenges emerged during the gold rush era, nanotechnology exploration will inevitably lead to the development of new tools to achieve new breakthroughs, the opportunity for creating enormous wealth, and unfortunately, the potential for environmental, health, and safety disasters. Although Single-walled Carbon Nanotubes undoubtedly will create disruptive technologies that will spin off many new jobs, it also has the potential for displacing existing workers unprepared to take on these new technologies.
The first fruits of nano R&D are already being harvested as disciplines as diverse as materials, electronics, biotechnology, and computing rush to exploit nanotechnology’s potential. Many consumers have already become familiar with nano-derived products, such as improved types of cosmetics, fabrics, paints, plastics, or personal electronics.
Nanotechnology offers all-but-unlimited opportunities for those who can develop the next exotic material or electronic component that is cheaper, better, and faster than today’s CMOS devices. It also holds huge promise for those who will create the tools needed to produce these materials and devices. Despite the recession, corporate and government labs around the world continue to invest billions in nanoscience research. Unfortunately, unless the public and private sectors work in cooperation to develop standardized test methods and guidelines, the transition from the laboratory to the marketplace could create many of the same problems as the California gold rush did, particularly for the environment. However, with careful planning, we can have the appropriate terminology, test measurement methods, reporting, and environmental, safety, and health safeguards in place early enough to ward off serious consequences.
Why Are Standards So Important?
Very simply, standards are crucial to achieving a high degree of interoperability, creating order in the marketplace, simplifying production requirements, managing the potential for adverse environmental impacts, and most important, ensuring the safety and health of those developing and using the next generation of materials and devices.
Standards for nano terminology, materials, devices, systems, and processes will help establish order in the marketplace. For R&D researchers and engineers, standards make it possible to make measurements and report data consistently in a way that others can understand clearly. Those responsible for developing standards will be at the forefront in understanding the need for, and creation of, new characterization tools, processes, components, and products to help jump-start this emerging field. This kind of approach can represent a competitive tool in global markets. Creating a standard in advance of the release of a new technology allows both manufacturers and consumers to gain greater confidence in it, promoting greater acceptance and faster adoption.
The following examples illustrate the importance of early standards development.
Carbon Nanotubes
Although some of the more sophisticated electronics and medical advances scientists have envisioned are still years down the road, the development of some nanoscale raw materials, particularly carbon nanotubes (CNTs), is already well underway. Years before CNTs were commercially available, industry observers heard how they would bring significant performance advantages to electronics, enhance materials to make them stronger and lighter, and might even be part of the solution to our energy problems. This industry buzz, plus the massive private and public sector investments in nano research, built interest at every level. In 2000, the late Dr. Richard Smalley spun off his work to form Carbon Nanotechnologies Inc. (now Unidym) with the goal of commercializing his method of producing large batches of high-quality nanotubes. Unfortunately, at that point, there were no manufacturing standards or guidelines for ensuring the reproducibility of the company’s manufacturing process. There were also no known test and measurement guidelines for verifying the reproducibility and proving results on a large scale. Given this, how would the company have assured its customers of the quality of its products? Or just as important, how could customers choose confidently among various manufacturers’ CNTs based on their product description?
Buying carbon nanotubes isn’t like buying baseballs or bananas-it’s impossible to judge their quality just by looking at them. En masse, CNTs basically look like a pile of soot. How can incoming inspectors verify what they have received? How do they know whether they are single-walled or multi-walled tubes? Given the different species of carbon nanotubes now available (tubes that are metal or semiconducting, based on their chirality), most companies looking to purchase nanotubes would have had no basis on which to ensure that what they received is what they ordered. However, with a standard in place, customers have the tools needed to verify the materials they are purchasing.
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