Nanogenerator harvests power from waves

'Piezotronics'
In addition, working with researchers at the National Tsing Hua University in Taiwan and SunYat-Sen University in China, Wang's group has demonstrated what it calls piezotronic devices—transistors, diodes and sensors made from piezoelectric materials.

The piezotronic transistor, for instance, controls conductance in its channel by bending it between the source and drain electrodes to produce a gate potential. Up to a tenfold change in conductance has been observed by flexing the piezotronic transistor, according to Wang.

The piezotronic diode harnesses the interface between an electrode and the stretched side of a flexed nanowire, thereby limiting current flow to one direction. And the piezotronic sensor flexes to measure a force as small as a nanoNewton, making the device sensitive enough to detect a single molecule, Wang said.

All of the team's nanogenerators and other piezotronic devices are fabricated from zinc oxide compounds that Wang claims are biocompatible, thus making them candidates for medical implants that, for instance, could measure blood flow, then generate their own power to relay that information wirelessly to diagnosticians.