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DESIGNING efficient nanoelectronic devices could be more difficult than previous thought, as researchers from Monash University find nanoscale components are subject to severe electronic effects.
At the nanoscale, electronics components behave in very strange ways. As electronics continue to miniaturise, even a single atom can influence or disrupt the flow of electrons.
To investigate and reach a better understanding of how to control nanoscale dynamics, Agustin Schiffrin, a lecturer in physics at Monash University, teamed up with Katherine Cochrane, a PhD candidate in Atomic Imaging, and Sarah A. Burke, assistant professor in neuroscience from the University of British Columbia.
Of particular interest to the researchers were the interactions of electrons at the boundaries of materials, especially because as the size of components decreases, more electrons are likely to be close to an interface.
In solar cells, for example, the positive and negative charges are separated within a few nanometers at the boundary between electron donating and electron accepting materials.
Light-emitting diodes can work the other way around: they can generate light when positive and negative charges recombine at these boundaries.
The researchers looked at two-dimensional nano-clusters of different sizes and shapes, composed of organic semiconducting molecules on a thin insulator to see how electronic properties varied at different locations on them.
They examined the atomic-scale structure and electronic properties of these organic nano-clusters using a scanning tunnelling microscope.
They were able to create an image of the surface of the material to understand where atoms and electrons are located. Their experiments showed that the electrons of the molecules at the edge of the nano-islands behaved dramatically differently than those in the middle.
Importantly, these differences in electronic behaviour depended strongly on subtle variations of position and orientation of the molecules nearby.
When an electron is removed at a specific location in the centre of a nano-island, the electrons of the surrounding material react, moving towards the positive charge created by the electron removal.
Similarly, if an electron was added, the surrounding electrons moved away from the negative charge created by the electron addition. This collective motion of electrons polarises the surrounding environment and stabilises the created charge: the charge gets screened.
In contrast, when an electron is removed or added at the boundary of the nano-island – where transfer of electrons becomes important for technological applications – the created charge is screened a lot less efficiently.
The researchers found that the energies involved in this action are very large. Not only do subtle features of the nanoscale structure of components induce severe electronic effects at their interfaces, but also the influence of these effects becomes more important as the size of components shrink.
To ensure effective engineering of nanoscale electronics, it will be crucial to control the arrangement of atoms and molecules at the interfaces between these components, and do this with incredible precision.
Such small and precise tuning of atomic scale structure can be a challenge, but techniques like supramolecular self-assembly, where atoms and molecules arrange themselves in desirable patterns at the nanoscale, can be possible.