Nanotechnologists promise a lot: electronics forged from individual molecules, superstrong, lightweight materials, ultrafine capsules that carry drugs to specific organs or cells in the body. But to tinker with materials on that scale, researchers need tools to probe and nudge their invisibly small specimens. And manufacturers will need equipment to mass-produce these future marvels. Such instruments don’t come cheap. The going price for a nanomanipulator – a machine so named not because it is tiny itself but because it can move things around with nanometer precision – is tens of thousands of dollars. MIT mechanical-engineering professor and TR100 honoree Martin Culpepper believes he can produce better instruments for less than $3,000 apiece using a different approach to machine design. Existing nanomanipulators, he points out, “have got a bunch of different joints and linkages to assemble together.” Because the gaps between pieces can be many nanometers wide, this “old paradigm,” as he calls it, is impractical for nanoscale motion. Instead, Culpepper’s machine is built around one piece that bends and flexes ever so slightly. He shows TR’s Dan Cho how to provide supersmall movement without an astronomical price tag.
1. Like Butter. The nanomanipulator begins in a machine shop, where two of Culpepper’s graduate students, Soohyung Kim and Nathan Landsiedel, cut pieces out of metal. They place a plate of titanium on the bed of a water-jet cutter and feed instructions from a computer disk into the adjoining console. With a moving nozzle that shoots a millimeter-wide stream of water laced with particles of garnet, the machine can cut complicated shapes in a matter of minutes.
2. Flex Time. Culpepper holds out one of the newly cut pieces. This is the heart of his machine: three flat strips branching out symmetrically from a common center and surrounded by a wiry frame to form a vague triangle. There is purpose in this curious geometry. The center, or “stage,” of the triangle is where a probe would be fixed in a complete instrument. “You hold these three points,” says Culpepper, gesturing toward three washer-shaped fixtures suspended on the bent arms between the corners of the triangle, then “you push each one of these tabs to the side or up and down.” He indicates the ends of the flat strips and demonstrates how pushing two tabs toward each other moves the center away from them both. Press down on all three and the center moves upwards. By pushing different combinations of tabs, he can cause the stage to slide or twist in any possible direction. This is what engineers call six-axis motion, something existing nanomanipulators struggle to achieve.
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