Jun 24, 2019 | Updated: 08:43 AM EDT

Bending the Norm on Nanowires

May 27, 2019 01:55 PM EDT

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Nanowires form transparent and flexible conductive layers that can be used for improved stain sensors, solar cells and next-generation mobile phones. Applying nanotechnology in electronic devices requires a lot of testing of individual, tiny components to make sure that they will stand up to use.

Silver nanowires show a lot of promise as connectors that could be arranged in near-transparent, flexible meshes for touchscreens or solar cells, but it is not clear how they will respond to prolonged stresses from carrying current and bending.
Testing the bulk properties of a large sample of nanoparticles is easy but it is not revelatory. But adopting transmission electron microscopy or TEM makes it possible to study and examine individual nanoparticles. Ph.D. student Nitin Batra and his supervisor Pedro Da Costa are at the forefront of developing new TEM techniques. This research has allowed them to study and examine single silver nanowires in detail.

"A major part of our work has been designing and fabricating sample platform prototypes (or chips) for TEM, which allow us to characterize and manipulate nanomaterials with an unsurpassed spatial resolution," says Batra.

To improve on expensive commercially available chips that have a very fragile membrane to support nanoparticles, Da Costa and Batra, with help from Ahad Syed of the Nanofabrication Core Labat KAUST, have now submitted to patent their own reusable and robust chips that do not require a membrane.

The researchers suspended silver nanowires from platinum electrodes over their TEM chips that are custom-made and applied a range of voltages until the nanowires failed due to heating by the electrical current. They found that straight nanowires tended to snap when they reached a high current density, and it is determined by the local structural defects.

Another behavior that is seen when the nanowires were bent from the beginning is that the samples tended to buckle instead of snapping at high voltage and it exhibited an ability to self-heal because they remained held together by the carbon coating that is on the outside part of the wires. Some nanowires even showed resonant vibrations before they failed.

"Many devices are expected to undergo repeated bending and twisting by the end-user, which means that it is not realistic to limit the study of the electrical response of silver nanowires to straight configurations," says Batra. "Our results suggest that the failure rate of such devices could be minimized by using bent nanowires instead of straight ones. The self-healing capability could effectively delay the breakdown of the circuit."

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