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Three SNS instruments will explore the new world of nanostructured materials.
The first three instruments to accept beams from the Spallation Neutron Source in 2006 will allow researchers to weigh in on matter at the nanoscale. Both literally and figuratively, a bridge connects the SNS to another major Department of Energy scientific user facility—the new Center for Nanophase Materials Sciences. Researchers at the nanocenter seek to learn more about biological and polymeric membranes, nanomagnetism, catalysis at the nanoscale, and energy production challenges. Their tools will include the recently commissioned SNS liquids reflectometer, magnetism reflectometer, and backscattering spectrometer. Proteins buried in cellular membranes allow transport of materials into and out of cells. "Using the new instruments at SNS, we will measure vibrations in membranes and relate these dynamics to the opening and closing of membrane channels and transmission of information and materials into, out of, and between cells," says Ian S. Anderson, director of the SNS Experimental Facilities Division. "We can determine membrane structure by replacing hydrogen atoms with heavier deuterium atoms, which scatter neutrons differently. In this way, we can highlight the positions of proteins, molecules, and functional groups attached to, or incorporated within, membranes." To use neutrons to study a membrane’s molecular motions, researchers must not restrict motion by fixing the membrane to a solid surface. Studies at ORNL’s nanocenter demonstrate that membranes can be suspended over an array of nanofibers, preserving their flexibility and biological function. Furthermore, this "nanostructured scaffold" could be used to insert foreign proteins, for example, into the cell through its membrane. The changes in membrane structure and dynamics that result could be studied using neutron scattering. The liquids reflectometer can measure how atoms are arranged at the surface and below a few hundred nanometers. The instrument may be useful for determining the part of a cell membrane surface most vulnerable to attack by the AIDS virus or the way bacterial toxins infiltrate and destroy cells by creating pores in their membranes. These structural measurements can be coupled with information on membrane motions obtained from the backscattering spectrometer, providing unique insights into how membranes work. Creating an electronic device that packs encyclopedic amounts of information into an amazingly small volume and retrieves the data incredibly fast is one possible outcome of nanomagnetism research. Such devices require the use of electron spin rather than electron charge to store and transmit information. In nanostructured, thin-film, "spintronic" devices, electron spins are relatively aligned to the device’s magnetic direction. The read head used to extract the information stored on computer hard disks is a good example of a modern spintronic device. "Polarized" neutrons of known spin reflected and detected by the SNS magnetism reflectometer will provide unique data on magnetic direction and structure in the deeply buried magnetic layers that compose spintronic devices. Such information will guide the development of these devices as well as tomorrow’s quantum computers. Most catalytic reactions responsible for many commercial products occur on surfaces. Because nano-sized particles offer increased surface area, researchers believe they could be ideal catalysts. The SNS instruments will help researchers follow the adsorption of molecules on catalytic nanoparticles and the resulting structural changes. The backscattering spectrometer and planned instruments will probe the dynamic processes of adsorbed molecules, such as diffusion, rotation, and vibration. Future SNS measurements of the atomic structure of catalytic nanoparticles will enable scientists to develop more efficient catalysts for removing pollutants from car exhaust. Neutron research and nanoscience may light the path toward a "hydrogen-based economy" by improving fuel cells and hydrogen storage systems. The SNS backscattering spectrometer will enable researchers to track the diffusion of hydrogen in carbon nanotubes to predict how well tiny tubes can store and release hydrogen for use in power-producing fuel cells. The instrument will also enable studies of methane hydrates found in the ocean and Arctic permafrost, compounds that are potential sources of hydrogen and temporary storage media. Over the next decade, the bridge between ORNL’s Spallation Neutron Source and nanocenter will symbolize the value of linking two worlds of amazing discovery. Together, they will help shape the future of neutron science and nanotechnology, as well as their impacts on a limitless range of new materials for American industry.
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