麻豆传媒

A nanoscale welding technique has been developed by sparking high-temperature chemical reactions inside 鈥渘anopores鈥�.

The technique could ultimately be used to weld together nanoscale components and could also lend itself to nanoscopic chemistry experiments, say the researchers.

By lacing a micrometre-thick film of aluminium with nanoscopic holes and filling the holes with iron oxide, the researchers produced a high-temperature 鈥渢hermite鈥� reaction.

This reaction is used every day in welding and fireworks, and as a simple but spectacular classroom chemistry demonstration. Thermite reactions are normally produced by heating a mixture of aluminium and iron oxide powders, and produce fiery sparks and molten iron.

Etching nanopores

鈥淚nstead of just making a wire or a tube like lots of nanotechnology projects, we wanted to actually try and do some chemistry,鈥� says Christiaan Richter of Northeastern University in Boston, US, who presented his research at the National Meeting of the American Chemical Society in Atlanta this week.

Richter and colleagues used electrochemical acid etching to create 鈥渘anopores鈥� 20 nanometres wide in the surface of aluminium film, at a density of more than a billion per square centimetre.

The pores were made by placing the aluminium film in a solution of weak acid with an electric current running through it. At first, random dimples appear in the aluminium鈥檚 surface, but if the right current is applied for long enough nanopores form in a regular hexagonal arrangement. This happens due to small differences in electric potential across the surface of the film, which affect the acid solution.

Using a similar electrochemical trick the researchers then filled the nanopores with iron oxide, triggering a reaction that produced temperatures up to 4000掳C.

Nano-receptacles

Richter says nanoscale thermite reactions could perhaps be used to 鈥渨eld鈥� together molecular machines. But the real value of the technique could be more wide-ranging, he believes. The holes filled with iron oxide could be used as nano-receptacles for other chemicals, giving chemists finer control of chemical reactions, he says.

鈥淭his is something we couldn鈥檛 do before 鈥� chemists have to rely on random processes to bring reactants together,鈥� Richter told 麻豆传媒. 鈥淏eing able to impose order on such a small scale could make a big difference.鈥�

For example, Richter suggests the technique might be used in manufacturing metal compounds. 鈥淭he strength of alloys depends on how many flaws they have, and the technique we developed could allow very ordered arrangement of different compounds to make sure no flaws form,鈥� he says.