Forging Flexible Silver Nanowires

One of the key goals at the moment when it comes to applied electronics is to both make everything smaller and to also make it flexible. By building the devices onto a flexible foundation layer the hope is we can create synthetic skin for robots or wearable electronics not to mention all the other obscure engineering applications. One of the most important parts (some would even call it the most essential part) is to create a flexible nanowire. Wires are traditionally made out of metal and this is because metals will always conduct electricity better and more reliably than any other group. Although on a macro scale metals are malleable, their high Young modulus means they are quite rigid when small enough samples are taken. Also the surface texture of metal nanowires produced so far is very rough and is a well accepted fact that sharp surfaces leak electric field more than smooth ones.

This new paper’s primary goal was to fabricate nanowires made of metal that are both flexible and smooth without sacrificing the conductivity to do so. Ordinarily imprinting lithography is performed at low temperatures and pressures in order to produce nanowires and although this method is effective at producing completely uniform structures the product requires processing multiple times and will certainly obtain a defect no matter the care taken. Another method is ink jet printing where the metal atoms are sprayed onto a flexible substrate. This does produce a flexible wire but the lack of precision with the spray method results in the rough topology described. The new idea is to use a pair of lasers to directly apply the the metal ions, silver (Ag) in this case, onto a layer of polyethylene terephthalate (PET). One of the lasers will pulse and so will through photoredcution cause the silver to gain electrons. The other laser is continuous and will use optical trapping to position the particles to precisely the right place. The produced nanowires were elecromechanically stable and also retained their conductivity (with only a small resistance increase of less than 50 Ohm after being bent and realigned 2000 times).  All in all this provides a method that with some refining could be used to produce flexible silver electronics of a much higher quality than those already in production.

Paper links: The Conductive Silver Nanowires Fabricated by Two-beam Laser Direct Writing on the Flexible Sheet

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