Figure 1. Single-step method produces zinc oxide nano-tetrapods that directly form a bridge between contacts on chip. Source: Yogendra Mishra, Kiel University.
These sensors may lead to better industrial flame detectors and other devices, the researchers believe. "Nanostructures made from zinc oxide are highly interesting for multifunctional applications, due to their sensitivity to UV light and their electrical and mechanical properties," adds Mishra. For instance, such a sensor might be able to provide an alarm when ambient atmospheric conditions change, he explains.Most current nano-sensor synthesis methods require sophisticated equipment and a follow-up step for attaching the sensors to chips. In contrast, the new technique involves a single step. A simple oven or an airbrush-gun-type burner converts zinc micro-particles into zinc oxide nano-tetrapods that deposit on pre-patterned chips, forming bridges between gold contacts set 2–10 microns apart (Figure 1). The process takes place in a normal oxygen environment, with the amount of oxygen needed regulated by the flame itself, the researchers explain. More details on the fabrication of the sensors appear in a recent article in Advanced Materials.
"This burner-flame transport synthesis method allows us to grow the zinc oxide nano-microstructures directly on the chip — and that only takes a few seconds. It is just a matter of driving the chip through the flame while the nano-tetrapods assemble themselves onto it," notes Mishra. Moreover, the high temperature of the flame ensures good quality contacts between the nanostructures and the chip. The fast and simple fabrication process may enable production of hundreds to thousands of sensors per hour — and the sensors themselves have no disadvantages versus conventional zinc oxide ones, he believes."A prototype with compact electronics should be fabricated as [a] demonstrator device for a flame detector. Upscaling of nano-tetrapods is already on the way. We are working with a start-up company as these nano-microtetrapods can be utilized in many ways," Mishra says.