Luminescent nanowires grow horizontally

01 May 2008

Ultra-long gallium oxide nanowires that emit blue light could benefit biological science

Gallium oxide (Ga₂O₃) nanowires measuring hundreds of microns and even millimetres in length could prove useful in helping microbiologists to track the migration of cells across a substrate. Grown by scientists in Taiwan, the linear structures emit blue light (400–500 nm) when irradiated with an ultraviolet source (254 nm) and provide a much clearer reference pattern compared with a series of quantum dots.

There are other advantages too, especially when it comes to manipulating the material. "With ultralong nanowires, the use of an electron microscope may be unnecessary to guide the fabrication of electrodes for device measurement," Michael Huang of National Tsing Hua University's Nanomatarials Laboratory told nanotechweb.org. "Instead, you might be able to use a good optical microscope."

Horizontal growth
The researchers found that they could encourage the nanowires to grow horizontally by first annealing the silicon substrate in oxygen to form a 100 nm-thick SiO₂ film. Next, the surface was sputtered with a gold catalyst and then placed inside a tube reactor raised to a temperature of 750 °C. Inside the reactor, the sample is exposed to a source of gallium and subjected to a continuous flow of nitrogen gas for five hours.

According to Huang, the sample's SiO₂ layer appears to provide the oxygen source that facilitates the Ga₂O₃ nanowires' horizontal growth pattern. The team hopes to exploit this effect as a means of offering better directional coverage. In addition, the scientists plan to use a similar reaction scheme to explore the horizontal growth of other oxide nanowires.

The researchers presented their work in Nanotechnology.