Credit: © 2007 IOP

Chemical vapour deposition (CVD) is a powerful technique for growing nanostructures of various shapes. The way in which CVD operating conditions affect the shape of the product, however, is poorly understood. Now, by varying the catalyst and source materials, Youguo Yan and co-workers1 at the Chinese Academy of Sciences in Hefei, China can controllably synthesize nanoarrows and other nanostructures made of indium oxide — a semiconductor material widely used in electronics.

In their method, indium metal is deposited onto a silicon wafer inside a furnace. As the wafer is heated, the indium film coalesces into droplets. When oxygen gas is introduced into the system, the indium droplets grow into a truncated octahedron of indium oxide through a proposed evaporation–absorption mechanism. The sides of the octahedron stop growing once they become perfect planes, leaving the bottom plane the only place for further growth. This process results in an arrow-like nanostructure consisting of an octahedral 'head' and a rectangular 'shaft'.

In similar experiments, when Yan and co-workers used silicon wafers coated with gold, they were able to grow In2O3 nanowires. When a mixture of indium oxide and carbon powder were used as the source materials, a different In2O3 morphology — nanorods — was obtained. This versatile and controllable CVD approach could be further modified to make designer functional blocks for future nanodevices.