ARCHIVED - Researchers create next generation "nanowires"
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June 08, 2008— Ottawa, Ontario
|Using block polymers, Dr. Buriak and her colleagues have created straight, circular and other patterns of nanowires.|
Researchers at NRC and the University of Alberta have cleared a major hurdle facing the nanotechnology revolution by producing tiny, nano-sized wires on silicon chips.
This feat – reported in the August 2007 issue of Nature Nanotechnology – represents "a solution to the problem of how to integrate existing chip technology and future nano-electronic components," says Dr. Jillian Buriak, leader of the materials and interfacial chemistry group at the NRC National Institute for Nanotechnology (NINT), and a chemistry professor at the University of Alberta. Her group's achievement also paves the way for the development of nano-sensors with medical or environmental applications.
Nanotechnology is the application of science and engineering at the atomic scale. It facilitates the construction of new materials and devices through the manipulation of individual atoms and molecules – the building blocks of nature. Forecasts by the U.S. based National Science Foundation predict that the market for nanotechnology-derived goods and services will reach US $1 trillion by 2015.
Using standard techniques such as electron-beam lithography, "it's easy to make very small features on silicon or other materials that are less than 40 nanometres in width," says Dr. Buriak. "But this process is far too slow and expensive for manufacturing purposes, so we wanted to see if we could use molecules that 'self-assemble' to do the hard work for us."
The NINT team focused on a class of molecules called block copolymers. "These molecules are compatible with silicon-based semiconductor fabrication methods, so you can easily incorporate them into existing processes without much trouble," says Dr. Buriak.
She and her colleagues used some block copolymers that naturally form into horizontal lines on surfaces. "If you etch trenches that are about 30 nanometres in depth into silicon, and add block copolymers, the molecules will actually align themselves in a straight line or circle, depending on the pattern you make," says Dr. Buriak.
Block copolymers are polymers composed of two or more distinct chains, attached by covalent bonds.
"It's like a party involving a bunch of chemists and a bunch of artists," says Dr. Buriak. "At the beginning of the evening, they may mix a little, but by the end, after several drinks – we'll call that the solvent – all of the chemists will likely be in one corner gossiping and all of the artists in the other corner," she says. "If you 'covalently attach' them by having everybody hold hands, they are still separate groups, but stuck together."
"These molecules just do it by themselves, without any outside prodding, other than the trench that we create," she stresses. "They will go around corners and self-assemble into interesting shapes." Building on this, the NINT team has figured out how to convert the aligned molecules into continuous metallic wires and how to measure their electrical conductivity.
Other researchers have previously shown how to manipulate block copolymers, but Dr. Buriak's team is the first to show that they can be made into something useful like wires. In one experiment, her team produced 25 parallel platinum nanowires – each one measuring only 10 nanometres in width, but extending to a length of 50 microns (50,000 nanometres).
Since publishing their initial study, the NINT researchers have demonstrated that the self-assembly process works on a variety of metals and magnetic substances, including copper, cobalt, iron oxide and iron. Their next goal is aluminium. "We would also like to incorporate two or more metals so they interweave, or different materials, where one is a metal and another is a semiconductor," says Dr. Buriak. One of the potential applications her team is investigating is whether self-assembled nanowires can be used as very small sensors.
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