The process used to produce the arrays involves evaporating a thin layer of gold onto the substrate, where it acts as a catalyst for nano-wire growth. The zinc oxide crystals look something like a forest without branches. To improve the adhesion of the nanowires with the substrate, we have added a thin layer of polymer onto the substrate after growth so that the roots of the nanowires are partially embedded. We have achieved electrical output of about 10 milli-volts and 800 nanoamperes from a nano-generator that is about six square millimeters in size. We have also shown that nanogenerators can be arranged in series to improve the output voltage and in parallel to improve the output current, as is commonly done with power sources such as batteries or fuel cells. But to produce higher voltages, we need to make nanowires with identical height and diameter.
Nanogenerators may never power our homes or even our flashlights; the amount of power available from them will be quite small. But nanowire arrays can be ideal generators for devices that need to work only intermittently, such as sensors that collect and transmit data for one second of every minute. In the years to come, nanogenerators will be used to harvest and recycle the energy wasted in our daily life, such as that created by pressure changes in a car tire, a moving vehicle’s mechanical vibration or even the fluttering surface of a camper’s tent. Consider how many small energy resources are all around us.