Quick and easy nanoarrays

Materials World magazine
1 Aug 2008

A fast and simple technique for producing nanostructured arrays is claimed to have been developed by researchers at Oxford University, UK. The technology allows a variety of nanostructures to be produced – dots, needles, rings and rods – while purportedly avoiding the problems associated with focused ion beam (FIB) technologies. The arrays could be used for data storage in advanced optical, electronic or magnetic applications.

Traditionally, FIB methods require wet chemical etchants or templates, which have limited accuracy and achieve poor aspect ratios. The Oxford method uses lithographic patterning, followed by rastering with FIB to create a gallium arsenide or silicon array. The resulting effect of the ion beam on the top layer of the iron is small, says Dr Yizhong Huang of Oxford’s Department of Materials.

‘The amorphous layer resulting from ion beam irradiation on the iron surface was observed to be a few nanometers,’ says Huang. ‘In addition, the final quick scan of the pillar patterns using a relatively small beam current (around 100pA) significantly reduces any artefacts that were formed by the ion beam sputtering.’

The technique produces an array in less than three minutes. Its structure depends on the ion dose or exposure time. A lower dose creates the rounded dots, while a higher dose produces pointed needle shapes.

The precision of the nanoarrays is also good, adds Huang, with a ‘site specific area of a few nanometers as related to the resolution of the system’. He says the fabrication costs are ‘a small amount of the usage time of a FIB system’.

The votex state magnetisation exhibited by the resulting multilayer structures makes them ideal for data storage, as well as magnetic force microscopy (MFM). ‘The sharp tips of the nanoneedles can be used as a probe in MFM,’ says Huang. ‘The iron particles located on top of the needle are magnetic, so the interaction between [them] and magnetic samples would allow the spatial distribution of magnetism to be mapped.’ The arrays could also be used in photoluminescence, or as templates to trap biological materials such as cells or DNA.

Beyond gallium arsenide and silicon, Huang believes other semiconducting materials or even metals could be used.

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