A hollow tube made from 42 atoms of gold has been added to chemists' list of curious target molecules to synthesize. Theoretical calculations show that the tube should be more stable than similar clusters of gold atoms, and could have important electrical and chemical properties.

Ying Liu and colleagues at Hebei Normal University, Shijiazhuang, China1 used a variety of different calculations to assess the stability and form of similar structures ranging from Au32 to Au72.

Their calculations included density functional theory, which relies on the principles of quantum mechanics to calculate the position and energy levels of atoms and electrons in the structure.

The structure with 42 gold atoms was the most stable of all the candidates tested, although Au47 showed similar characteristics. If inorganic chemists are able to synthesise the tube, it would measure just under a billionth of a metre across, the team say.

Fig. 1: Forty two gold atoms should form a stable tube, measuring just a billionth of a metre across.

Scientists have previously made hollow gold clusters containing around 20 atoms, but this is the first time that such relatively large hollow gold nanotubes have been theoretically predicted, says Liu.

“The huge nanotubes are expected to demonstrate some attractive features and applications in this field,” he says. Gold clusters have recently been found to catalyse the oxidation of carbon monoxide, an important industrial reaction, for example. The hollow gold tubes would present a relatively large surface area compared with a solid cluster of the same number of atoms, so the tubes could provide a way to make gold less expensive as an industrial catalyst.

The team's calculations suggest that the Au42 tubes should be semiconductors, which would make them potentially useful as components in spintronic devices, where the spins of electrons are used to carry information. Interestingly, they also found that it was not just the outermost electrons of each gold atom which determined their electrical and chemical properties— electrons closer to the atomic nucleus also play a significant role, Liu says.

The scientists plan to investigate the growth of clusters containing between 20 and 32 atoms, and explore how electrons are transported through gold nanotubes and nanowires.