Nickel in Nanotechnology
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PURE NICKEL trusses on the 1-to-100-micrometre scale could be used in a wide range of minature devices |
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One of the emerging technologies of the 21st century may rely on nickel
Nickel magazine, Jun. 00 -- In a technological age that promises to miniaturize everything
from motors to computer chips, nickel could very well play an increasingly valuable role. This role is
already reflected in the emerging field of micro-electro-mechanical systems (MEMs). MEMs are tiny mechanical
components -- some no larger than a grain of sand -- that usually contain integrated electronics. A handful
have already found commercial applications, from silicon-based pressure transducers that provide precise
measurements for medical monitoring to sensors designed to activate airbags in cars.
Industry observers predict that MEMs will do for mechanical components what microchips did for electronics. Indeed, the MEM market is expected to grow to more than US$5 billion by 2002, according to Cronos Integrated Microsystems, the first commercial enterprise to focus exclusively on MEMs products.
Some MEMs, including those applicable to biomedicine (such as protheses), defense systems (such as sensors to detect chemical and biological weapons) and portable consumer products (power supplies, for example), require three-dimensional metallic components. This is where nickel comes in.
Electro-deposited nickel gives structural integrity to 3-D components. In fact, microelectrodeposition can be thought of as the small-scale equivalent of casting and welding used to manufacture mechanical structures at the macro level, says George Whitesides, professor of chemistry at Harvard University.
"The actual amount of nickel that's involved is minuscule, but the value that the nickel provides is very high," says Whitesides.
Whitesides is testing nickel for use in 3-D metallic structures ranging from heat exchangers to components of small aircraft. His team combines electrodeposition with lithography, a set of techniques for pattern transfer, to build the microtrusses.
"The reason for working with nickel," Whitesides says, "is that it responds to electrochemistry, has good mechanical and corrosion properties and is inexpensive. It is strong and cheap and easily processed in this particular style."
For example, one technique routinely produces metal features at the 1-to-100-micrometer scale. Electrodeposition then transforms the planar metallic structures into minature 3-D devices by joining the separate 2-D components together.
Nickel could even be used in biomedical applications, such as implants that dispense drugs, though the metal would likely be coated to prevent possible allergic reactions. The metal's magnetic properties make it a natural choice for magnetic applications.
Alternative materials for 3-D applications include welded copper, material that has been machined out of silicon and, for biomedical purposes, stainless steel, titanium, and gold-plated materials.
By testing several different materials, the Harvard team hopes to develop a range of microstructures that cannot be produced economically by conventional means.
"We've reached the point where we can demonstrate clearly that one can make interesting structures," says Whitesides. "Now the question is, Are these structures sufficiently interesting that they will be worth someone's effort to commercialize?"
Once the components pass applications testing, commercialization will be assisted by the fact that the devices are uncomplicated and inexpensive to produce.
By Virginia Heffernan, a Toronto-based science writer
Photo: HARVARD UNIVERSITY
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Prof. George Whitesides |
