In this research supported by the Analytical and Surface Chemistry Program, new optical methods will be developed to analyze samples of single-walled carbon nanotubes. These nanotubes are novel molecular-scale structures with remarkable electrical, mechanical, and optical properties that will lead to important future applications. However, the nanotubes are formed in a variety of similar structural forms that are difficult to distinguish and separate. The results from this project will make it possible to use relatively simple laboratory measurements to quickly determine not only which structural forms are contained in a nanotube sample, but also how much of each form is present and how perfect or damaged the sample is. The new analysis methods developed in this project will have a range of impacts. First, they will be very valuable to basic scientists who need well-characterized samples to perform their nanotube research. Second, reliable and standardized characterization will speed the commercial production and industrial use of carbon nanotubes. Finally, the project will advance the scientific training of undergraduate, graduate, and postdoctoral students (including women and underrepresented minorities) by giving them hands-on research experience vital to their scientific education and professional development.
This research project was aimed at understanding how carbon nanotubes interact with light and devising improved methods for using light to find the composition and condition of nanotube samples. Carbon nanotubes are molecular-scale tubes made of chemically bonded carbon atoms. They have remarkable chemical, electronic, and mechanical properties that promise many important real-world applications. Although they are not found in nature, carbon nanotubes can be artificially grown by special processes that produce them in a variety of structural forms. However, it has been challenging to determine exactly which forms are present and how many defects the nanotubes contain. Building on a breakthrough discovery from 2002, we have pushed forward to develop advanced optical analysis devices and techniques for carbon nanotubes. Our research takes advantage of the fact that nanotubes can emit characteristic near-infrared light "signatures" when excited with visible light. Custom instruments developed and refined as part of the project use this effect to detect tiny trace concentrations of nanotubes in complex samples. This enables important environmental and biological studies involving nanotubes. We have also used the light emission of nanotubes to view them individually under a specialized microscope and thereby gain new insights into their physical and chemical properties. We discovered a simple chemical reaction that transforms nanotube light emission in novel and useful ways just by adding a few oxygen atoms to the tube's surface. This effect is related to our discovery that when a nanotube is energized by light, the excitation is not fixed in position but can move surprisingly far along the tube's axis. We also made real progress toward a major goal in the field: sorting mixtures of nanotubes according to their structural forms. A key step in this work was using our near-infrared optical methods to efficiently guide our separation efforts. The achievement of refined sorting is particularly important because it provides the nanotube research community with samples of unusual purity that can lead to further scientific discoveries and enable practical applications.
