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The many faces of a single molecule
02 December 2009
Scientists in Japan show that the electronic properties of simple molecules are different when they change shape.
Single molecule based electronic circuits are anticipated to be a crucial technology in the computers of the future. But the molecular components need to have predictable electronic properties, which may not be as easy as thought say Anirban Bandyopadhyay and Satyajit Sahu, at the National Institute for Materials Science, Tsukuba.
Bandyopadhyay and Sahu have discovered that simple distortions in molecules, which leave them chemically identical but a different shape (or conformation) can change the electronic properties. Previously, an average result was calculated from a repeated experiment but this neglect's the influence of the molecule's conformation.
A different electronic response was measured for different conformations
The researchers deposited a dye molecule called Rose-Bengal onto a gold surface with a hydroxyl group pointing upwards to act as a tip for an atomically small scanning tunneling microscope (STM). The tip 'picked up' a single molecule and pulled it away from the surface, where the conductance between the tip and the gold surface was measured. At the same time, an electric field applied to the tip region oriented the molecule. Bandyopadhyay and Sahu could then determine which orientations and conformations corresponded to the different recorded conductivities by comparison with values derived from calculations.
'We have explicitly shown that a molecule could be a transistor, a switch, an op-amp circuit, or a diode-like-rectifier at any one time. It settles into one feature depending on the environment it is in when we take the measurement,' says Bandyopadhyay.
Single molecule electronics still seem a long way from providing reliable technology for continuation of the famous 'Moore's law' which predicts that the computing power of standard computer chips will double every two years. These new findings offer an alternative perspective on the field, reminding scientists that molecules do not display absolute properties independent of their environment, and that they cannot necessarily be considered simply as analogues of currently available macroscopic electronic components indicates Bandyopadhyay.
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Link to journal article
A new approach to extract multiple distinct conformers and co-existing distinct electronic properties of a single molecule by point-contact method
Anirban Bandyopadhyay, Satyajit Sahu, Daisuke Fujita and Yutaka Wakayama, Phys. Chem. Chem. Phys., 2010, 12, 2198
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