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From the Labs: Nanotechnology

New publications, experiments, and breakthroughs in nanotechnology–and what they mean.
January 1, 2007

Morphing Materials
New shape-memory polymers can take on three successive shapes

A new polymer morphs from one pre-programmed shape to two others: as the flattened tube (top) is heated, it opens up (middle); heating it further makes it shrink.

Source: “Polymeric Triple-Shape Materials”
Ingo Bellin et al.
Proceedings of the National Academy of Sciences 103(48): 18043-18047

Results: Researchers at MIT and the GKSS Research Center in Germany have engineered polymers that can be programmed to sequentially take on three different predefined shapes in response to changes in temperature.

Why it matters: Existing shape-memory polymers can assume only two shapes each. The addition of a third shape could enable, say, an arterial stent that could be inserted into an artery in a collapsed form, induced to open once in place, and later shrunk for removal. The researchers demonstrated such an intelligent tube, along with a structure that could be used in device manufacture to connect ­difficult-to-access parts.

Methods: Each of the new materials is a polymer network consisting of two different cross-linked segments that respond to temperature differently. The researchers first cast the material into its final shape–such as the shrunken version of the stent–using a standard plastic-molding technique. They then use a precise sequence of heating and cooling steps to “program” the other two shapes, taking advantage of the material’s different responses to different temperatures. Heating the material in two steps makes it revert to its intermediate, and finally to its original, shape.

Next Steps: The researchers must demonstrate that the materials are safe enough to be used in medical applications. They are also developing fastener materials that could be useful in manufacturing.

Invisible Transistors
A novel method could lead to see-through displays for windshields

Source: “High-Performance Transparent Inorganic-Organic Hybrid Thin-Film N-Type Transistors”
Lian Wang et al.
Nature Materials 5(11): 893-900

Results: Northwestern University researchers have fabricated high-­performance, transparent thin-film transistors (TFTs) using a low-cost, low-temperature method. They use indium oxide as both a semiconductor and a conductor, combining the inorganic material with organic insulators on top of a transparent substrate. The resulting transistors perform nearly as well as the much more expensive polysilicon transistors used to control pixels in high-end TVs and computer monitors.

Why it matters: The new TFTs could replace the opaque transistors used to control pixels in digital displays. Because the low-temperature method can deposit transistors on flexible plastics, it could lead to see-through displays affixed to curved surfaces such as windshields and helmet visors. The method is also cheap enough, and easy enough to adapt for large-scale manufacturing, that it could make such displays affordable.

Methods: On glass that’s been coated with a transparent electrode, the researchers deposit the organic insulating materials, which form a multilayered lattice. To deposit the indium oxide, the researchers use a standard technique called ion-assisted deposition, in which an ion beam controls the crystallization and adhesion of the oxide. Changing the oxygen pressure during the process varies the conductivity of the indium oxide, which can thus be used as a semiconductor in one part of the device and as a conductor in other parts.

Next Steps: Negotiations for licensing the technology have begun. Prototype displays could be ready within 18 months. The researchers hope to improve the performance of the transistors so that they could serve as processors or memory cells.

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