Top-down techniques for nanofabrication, such as lithography and etching, enable precise control over the positioning of components on the small scale, but it is difficult to produce high-quality structures. Conversely, bottom-up techniques produce high-quality components, but position control is a problem.

Gyu-Chul Yi from Pohang University of Science and Technology and colleagues1 have brought together advantages of the two approaches to grow zinc oxide (ZnO) nanoarchitectures from nanowalls in precisely defined positions. Their position control allows them to fine-tune the nanostructures, making it possible to optimise their field emission and produce lighting devices.

The ZnO structures were grown on silicon substrates covered with a very thin gallium nitride. When nanowalls were grown on these substrates under ‘normal’ conditions—600°C, using diethylzinc and oxygen—the walls grew in a random network morphology.

Fig. 1: A scanning electron microscopy image of one of the templated arrays.

Yi and colleagues succeeded in growing the nanowalls at the desired positions by first laying down a silica mask on the substrates using lithography. The walls were then grown as before, but this time they followed the outlines of the template yielding microscopic shapes ranging from simple circles to text (Fig. 1). The authors ascribe the selective growth around the template to nucleation at the edges of the template.

The researchers then produced zinc oxide nanotube arrays using the technique, and found the spacing of the nanotubes to be important for their field-emission characteristics. The arrays were also used to create high-performance light-emitting devices with the arrays located opposite a green-phosphor-coated glass. Applying an electric field to the arrays resulted in electron emission, causing light emission from the phosphor that was strong enough to be observed by the naked eye.

“This work can offer the shift from two-dimensional to three-dimensional integration for more sophisticated and functionally integrated device applications,” says Yi.

In the future, the authors hope to use the approach to improve nanodevice performances. “These nanoarchitecture arrays enable us to take advantage of accurately controlling positions, thicknesses, and compositions of quantum structures embedded in the nanoarchitectures,” says Yi. “All of which are necessary for fabricating high brightness LEDs.”