Credit: © 2007 AIP

Quantum mechanics allows an electron to travel between two metals separated by a barrier of infinite resistance, provided the barrier is only a few tenths of a nanometre thick. This effect is the basis for scanning tunnelling microscopes, which are able to measure atomically sharp features on a surface, but could it also be applied to a more everyday application?

Now, a group of researchers from the Commonwealth Scientific and Industrial Research Organisation in Australia show that changing the tunnelling resistance through films of gold nanoparticles that are linked together with organic molecules can be the basis for a simple — but sensitive — strain gauge1. Jan Herrmann and colleagues used an airbrush gun to spray gold nanoparticles functionalized with 4-nitrothiophenol on an inkjet transparency. By stretching the transparency over rollers, the group could change the width of the organic tunnelling barrier between the nanoparticles and hence the resistance of the film.

The change in resistance of the film in response to an applied strain is large — indicating a sensitivity about 50 times greater than standard metal foil strain gauges and comparable to those made from semiconductors. And, as they can be 'sprayed' onto an arbitrarily shaped or sized surface, these nanoparticle-film strain gauges may be considerably more flexible.