Fabricating Prestressed Conductors

MATERIALS SCIENCE For stretchable sensors, electronic textiles, and connectors to actuators, it would be desirable to have metal contacts that tolerate large reversible stretching. However, free-standing metal films begin to crack when stretched by only 1%, and those on substrates can be deformed by only a few percent before losing their conductivity. One way around these limitations is to build some “slack” into the metal films. Lacour et al. adhered gold films to rubbery polydimethyl siloxane substrates via a thin intervening layer of chromium. These gold films start off under a compressive stress that creates buckles or wrinkles, and the authors expected that the films could be lengthened by only a small amount before cracks would appear and electrical resistance would increase. Unexpectedly, the resistance increased linearly up to a strain of about 8%, at which point small cracks began to appear along the edges of the films. At a strain of 15%, cracks spread across the width of the films, but the resistance stayed finite until a strain of almost 23%. The authors suggest that a conductive layer, one atom thick, remained at the bottom of the fissures.— MSL Appl. Phys. Lett. 82 , 2404 (2003).