Intrinsically stretchable biphasic gold–gallium thin films. A) False color scanning electronic microscopy (SEM) image of a slightly tilted cross-section of the biphasic gold–gallium film on a PDMS substrate. The blue, yellow and gray colors correspond to the PDMS substrate, the biphasic AuGa2/Ga film, and a gallium bulge in the background, respectively. Scale bar: 500 nm. B) False color SEM image of the surface of the biphasic gold–gallium film. The yellow and gray colors correspond to the AuGa2/Ga film and the liquid Gallium, respectively. Color mask was obtained from backscattered electron detector (BSE) image. Scale bar: 5 μm. C) X-ray diffraction pattern of a biphasic gold–gallium film deposited on a PDMS substrate clearly indicating the position of the peaks corresponding to AuGa2 intermetallic compound (ICDD PDF Card 01-072-5268). Inset: the increase in baseline signal around 35° is attributed to liquid gallium. D) Picture of a biphasic gold–gallium film patterned by photolithography with critical dimension of 100 μm on a 40 μm thick poly(dimethylsiloxane) (PDMS) elastomer membrane. Scale bar: 5 mm; Inset scale bar: 500 μm. E) Stretchable multilayered matrix of green surface mounted light emitting diodes interconnected and powered through biphasic gold–gallium conductors. Scale bar: 15 mm. Inset: the LEDs are interconnected with two biphasic conductor planes; scale bar: 2 mm.
Researchers have developed conductive tracks that can be bent and stretched up to 4X their original length. They could be used in artificial skin, connected clothing and on-body sensors. They can be stretched a million times without cracking or interrupting their conductivity. Both solid and flexible. “We can come up with all sorts of uses, in forms that are complex, moving or that change over time,” said Hadrien Michaud at the Laboratory for Soft Bioelectronic Interfaces (LSBI).
Extensive research has gone into developing an elastic electronic circuit. It is a real challenge, as the components traditionally used to make circuits are rigid. Applying liquid metal to a thin film in polymer supports with elastic properties naturally seems like a promising approach. Owing to the high surface tension of some of these liquid metals, experiments conducted so far have only produced relatively thick structures. “Using the deposition and structuring methods that we developed, it’s possible to make tracks that are very narrow – several hundredths of a nanometer thick – and very reliable,” said Stéphanie Lacour, who runs the lab.
Apart from their unique fabrication technique, the researchers’ secret lies in the choice of ingredients, an alloy of gold and gallium. “Not only does gallium possess good electrical properties, but it also has a low melting point, around 30o,” said Arthur Hirsch, a PhD student at LSBI. “So it melts in your hand, and, thanks to the process known as supercooling, it remains liquid at room temperature, even lower.” The layer of gold ensures the gallium remains homogeneous, preventing it from separating into droplets when it comes into contact with the polymer, which would ruin its conductivity. http://actu.epfl.ch/news/stretchable-electronics-that-quadruple-in-length/
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