Atomic force microscope can write and erase nanowires on a perovskite surface
Researchers have created an atomic-scale ’Etch A Sketch’ that can inscribe nanowires onto a surface - and rub them out again afterwards. The finding could eventually lead to a new generation of nano-scale electronic devices to rival silicon for the processing and storage of information.
Jeremy Levy of the University of Pittsburgh in the US, together with colleagues from the Naval Research Laboratory in Washington, DC and the University of Augsburg in Germany, exploited the fact that the interface between insulating layers of two different perovskite crystals (lanthanum aluminate and strontium titanate) conduct electricity when a positive voltage is passed across them but becomes insulating again if the voltage is reversed.
’It has been shown that if you put a very thin layer of lanthanum aluminate - 1.2nm deep - on a thicker layer of strontium titanate, the interface between the two layers can be made conducting,’ Levy told Chemistry World. ’Instead of applying the voltage to the entire surface, we used the extremely fine tip of an atomic force microscope to apply a voltage only to the region directly below the tip. We showed that in this way we could effectively write a conducting wire across the interface that was less than 4nm wide. The process is reversible - we can erase the wire by reversing the voltage.’
The wires can also behave as nanoscale transistors, with the tip of the AFM acting as the ’gate’, controlling the flow of electrons using an electric field. The researchers also ’wrote’ a series of isolated islands into the surface which could potentially store information at a density 100 times greater than with magnetic media.
The effect is thought to occur because a sufficiently high electric field pulls oxygen atoms from the surface of the lanthanum aluminate, which in turn affects the energies of the electronic state in the strontium layer, creating an ’electron gas’ at the interface of the two layers that can conduct electricity.
Commenting on the new work, Robert Bowman of the Centre for Nanostructured Media at Queen’s University Belfast in the UK said, ’Levy’s team elegantly point the way on how control and manipulation of oxygen on interfaces can lead to differing conductivity behaviour and rightly point out the enormous potential that oxides might provide for next generation information processing applications.’
C Cen et al, Nat. Mat., 2008, DOI: 10.1038/nmat2136