AdvancedManufacturing.org
to make. The key lies in forests of carbon nanotubes, which can accurately print electronic inks onto rigid and flexible surfaces. The MIT group, led by A John Hart, has been working with carbon nanotubes for some time. “It’s somewhat serendipitous that the solution to high-
resolution printing of electronics lever- ages our background in making carbon nanotubes for many years,” Hart said. “The forests of carbon nanotubes can transfer ink onto a surface like massive numbers of tiny pen quills.” The team designed a “nanoporous”
stamp—more spongy than rubber and the size of a pinky fingernail, with features smaller than the width of a human hair—that lets the ink flow through the stamp and onto the sur- face to be printed. To make the stamps, Hart’s group used its previously developed tech- niques to grow carbon nanotubes on the surface of silicon in various pat- terns, and then coated the nanotubes with a polymer layer in order to make sure the nanotubes would not shrink after the ink was stamped. They then infused the stamp with electronic ink containing nanoparticles like silver, zinc oxide or semiconductor quantum dots. The group created a printing machine with a motorized roller and attached it to various flexible sub- strates. The researchers fixed each stamp onto a platform attached to a spring, which helped control the force used to press the stamp against the substrate—essential for printing tiny yet precise patterns. “We found, limited by the motor we used in the printing system, we could print at 200 millimeters per second, continuously, which is already competi- tive with the rates of industrial printing technologies,” Hart said. “This, com- bined with a tenfold improvement in the printing resolution that we demon- strated, is encouraging.”
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The ink patterns proved highly-conductive, and going
forward, the team plans to investigate the possibility of fully printed electronics. The research was published in the journal Science Ad-
vances. It was supported in part by the National Science Foundation and the MIT Energy Initiative.
March 2017
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