Credit: © 2007 The Japan Society of Applied Physics

Nanometre-sized hollow tubes with semiconducting, insulating or metallic properties are of interest for fabricating nanoscale optoelectronic devices. In particular, nanotubes made from ZnO — a wide-band semiconductor material — could potentially be used to make novel quantum ring structures for trapping magnetic fields. However, ZnO nanotubes made with template methods that require reactive-gas etching have extremely low crystalline quality and cannot be used for fabricating nanodevices.

Now, Guoqiang Zhang and colleagues1 of Shizuoka University, Hamamatsu, Japan and the National Institute for Materials Science, Tsukuba, Japan, have used conventional metal–organic chemical vapour deposition to synthesize high-quality vertically aligned single-crystal ZnO nanotubes. They were grown on LiAlO2 substrates using low pressures of the diethyl zinc and oxygen source materials. The use of hydrogen as a carrier gas resulted in ZnO nanowires, but when using a nitrogen carrier gas, single-crystal ZnO nanotubes with diameters in the range of 15–100 nm were formed.

The room-temperature green photoluminescence emission from the ZnO nanotubes was more efficient than from other nanostructures such as wires and rods because of the larger surface area to volume ratio of the nanotubes. It is suggested that these materials may find applications as catalysts and sensors in addition to offering a new route to quantum ring structures.