Special Report - Spotlight on Nanotechnology
Nanotechnology moves into the spotlight
It's science on the smallest of levels. It's the truth in the statement that good things come in small packages. Nanotechnology is an area of research and development that centers on phenomena that occur at dimensions so tiny that they're hard to imagine—in the range of one billionth of a meter. Yet the potential impacts are tremendous.
Pacific Northwest National Laboratory has embarked upon a Nanoscience and Technology Initiative to explore this new area of science. In addition to fundamental research, the projects in this initiative are examining potential applications that span from medical treatment to energy generation, electronics to specialty materials and beyond.
Years before nanotechnology became the buzzword at research institutions across the country, researchers at Pacific Northwest National Laboratory were studying how molecules arrange themselves to form materials on the nanoscale.
"This Laboratory started one of the first nanoscience projects within the Department of Energy complex about three years ago," said Jun Liu, a senior staff scientist in materials chemistry and research. "A small group of people in materials science, including Gregory Exharos, Pacific Northwest's Basic Energy Sciences materials program manager, have been pushing toward this for some time."
Pacific Northwest's research is focused on self-assembly—a new approach that allows materials to build themselves rather than forcing molecules into certain structures one by one. DOE's Office of Basic Energy Sciences is funding this fundamental science project to build a better understanding of how different combinations of molecules will arrange themselves into different structures, how these structures affect material properties and how to adopt this approach to build new materials.
Liu explained that organic and inorganic molecules, even a simple combination of soap and water, have a tendency to organize themselves into nanostructures. For example, depending on the proportion of soap, water and oil or salt in the mix, molecules will form nanostructures in the shape of spheres, rods or honeycombs.
The conventional method used to build specialized materials involves making a ceramic powder under high pressure and often involves high-temperature treatment. Self-assembly, on the other hand, can take place at room temperature. Materials created through self-assembly also could offer improved physical, chemical and biological properties for a broad spectrum of applications.
"We can build materials that can be used for some interesting things," Liu said. "For example, the tiny holes in a honeycomb-like structure could be used as a nanofactory to build something else. This could be a way to isolate and control chemical reactions or to store and stabilize materials such as proteins that typically don't last long in air."
This fundamental research on how molecules behave and interact also has been the driving force behind many specific projects at Pacific Northwest for other clients. Scientists are researching potential applications including microelectronics and catalysis.
Another potential application could be drug delivery. Pharmaceuticals would be stored within the large surface area of the nanostructure and then released slowly, for example when a person's body temperature reached a certain level. When the body temperature returns to normal, the drug delivery would automatically stop. This drug delivery technology is based on a new class of "smart" nanoscale materials developed at Pacific Northwest. These "smart" materials can respond and regulate their functions depending on the surrounding environment, similar to the way biological tissues function.
On first blush, two scientists striving to exploit unique electronic and magnetic properties of metal oxides that occur in the nanoscale may seem to be working toward the same end. They're using the same equipment and some of the same methods, but their research at Pacific Northwest National Laboratory and its potential applications are quite different.
At the heart of both project is molecular beam epitaxy equipment—an instrument that researchers use to generate beams of atoms in a highly controlled vacuum environment. The instrument directs these beams onto a surface where they condense and form crystalline materials with dimensions on the nanoscale.
Here is where the similarity between Scott Chambers and Yong Liang's research ends. Chambers and his colleagues are focusing on materials with only one dimension on the nanoscale, while Liang and his team are developing three-dimensional nanostructures called nanodots that are so small that about 100,000 of them would fit on the head of a pin.
These nanodots or quantum dots are metal oxide crystals that are like artificial atoms with unique electronic properties. "Unlike normal atoms, however, the properties of the nano-dots can be changed by changing the material size, material composition and how they interact with the substrate," said Liang, a senior research scientist who works in the Environmental Molecular Sciences Laboratory, a Department of Energy user facility on Pacific Northwest's campus.
Other research institutes are working with nanodots to build more efficient lasers or memory devices in electronics, but the research at Pacific Northwest is focused on applications more directly tied to DOE's energy missions.
Liang and his team are investi-gating the potential use of nanodots for generating hydrogen on demand, which would be useful in future fuel cell applications. He hopes to demonstrate the proof of this concept within the next year.
While Liang's research may someday be used to generate energy, the extremely thin sheets of metal oxides that Chambers and his fellow researchers are developing could potentially be used in a new kind of computing system known as a quantum computer.
"Conventional computing techniques are very rapidly reaching their limits. Probably by the end of the decade we'll reach a brick wall in terms of size, speed and power dissipation," said Chambers, a chief senior scientist who was the original developer of the molecular beam epitaxy equipment in EMSL.
Unlike electronic devices that use the charge of electrons to carry signals, quantum computing would utilize the spin of electrons, or the polarization of light. This approach potentially could greatly increase speed and lower the power dissipation in computing systems.
Chambers' team is sandwiching a sheet of crystalline zinc oxide only 10 atomic layers thick between two sheets of mixed zinc and manganese oxide, each about 500 atomic layers thick. When the two outermost sheets are attached to a battery to form a circuit, spin-polarized charges are transported into the ultrathin sheet of zinc oxide.
"The recombination of these electrons and holes—or missing electrons—occurs in the middle layer," Chambers said. "The holes, which have just one spin orientation will recombine only with electrons that have the same spin orientation. As a result, polarized ultraviolet light is emitted, which may be useful in optical quantum computing."
Chambers' research could lead to advances in medical diagnosis and treatment. His ultraviolet light emitting devices could be attached to the end of a fiber-optic probe and travel through blood vessels for direct ultraviolet irradiation to treat internal organs. Similar devices could be useful in photocatalytic reactors requiring ultraviolet sources, such as those designed to destroy toxic organic waste.
Scientists at Pacific Northwest National Laboratory who studied how ice on comets can store large quantities of gas and release them as the comets near the sun are applying the same approach to new research. They're learning more about how nano-structures could be used to control and enhance chemical reactivity.
Stemming from the ice research funded by DOE's Office of Basic Energy Science, Zdenek Dohnálek, Bruce Kay, Greg Kimmel, Scott Smith and their colleagues in Pacific Northwest's Chemical Structure and Dynamics group began pursuing additional projects to determine how molecules enter pores, get captured and are eventually released.
New knowledge in this area could lead to the development of more efficient catalysts, which are materials that modify and increase the rate of chemical reactions.
Their current research is focused on creating porous films—not ice. They're building an understanding of the chemical and physical properties of these materials and characterizing their structure. The scientists are learning about the materials' surface areas and where gases and liquids accumulate on the surface. Soon they will begin studying how their catalytic properties may affect chemical reactions.
To create the films, researchers use a process called ballistic deposition to shoot a beam of molecules at a controlled angle toward the surface of a material. As these molecules condense at low temperatures, they form a porous film.
Similar to the way that a porous sponge can soak up large quantities of water, the porosity of the film results in a large surface area where more atoms are available for reactions.
The filament-like structure of the porous film gives it a large surface area. Tiny dust particles that blocked the beam of molecules deposited on the surface caused the areas that appear empty.
"Virtually nothing is known about the fundamental chemistry of these nanoenvironments," said Dohnálek, a research scientist on the project. To date, most research in this area has been conducted by engineers who are interested in the dielectric and magnetic properties for potential uses in optics and electronics.
"We have the ability to create chemically tailored materials with various nonstructural features that can lead to enhanced selectivity and reactivity," said Kay, a senior chief scientist. "It takes specialized equipment to grow these kinds of materials and even more sophisticated instrumentation—like what we have available here—to study them," Kay said.
This work takes place at the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE user facility operated by Pacific Northwest.
Pacific Northwest National Laboratory and the University of Washington are preparing to form a joint institute in early 2001 that will bring together the resources of both institutions to pursue major discoveries in nanoscience and nanotechnology.
Once official agreements are in place, graduate and postgraduate students and faculty from the University of Washington will collaborate with scientists at Pacific Northwest National Laboratory on joint research projects. These combined research teams will have access to the unique equipment and instruments of the William R. Wiley Environmental Molecular Sciences Laboratory, a U.S. Department of Energy national user facility.
"We're looking forward to working together more closely with the University of Washington and the expanded opportunities that this joint institute will present," said Bill Rogers, associate laboratory director of Pacific Northwest's Fundamental Science Division.