Credit: © 2007 ACS

Recording nanoscale information on organic thin films may be a route to ultrahigh-density information storage. However, even the best writers could use an easy way to correct their mistakes.

Now, Hongjun Gao and co-workers1 at the Chinese Academy of Science in Beijing have synthesized a new molecule (which they called 'H2 rotaxane') for making erasable and rewritable organic thin films. By applying positive and then negative voltage pulses to the films with a scanning tunnelling microscope tip, the conductivity of the film below the tip can be changed from high (write) to low (erase). The appearance and erasure of 'written' dots can be seen in atomic force microscope images, which are sensitive to the surface conductivity. However, topographic images show that there is no change in the height of the surface, suggesting that the changes are purely electronic.

The rotaxane in this study has a dumbbell-shaped axle component encircled by an electron-deficient ring-shaped molecule. The ring can move between two different electron-rich recognition sites, which correspond to distinct conductance states of the molecule. It is suggested that, because of its structure, this molecule is able to move back to its ground state more readily than a similar compound previously studied by Gao and co-workers, which makes it easier to 'erase' old information and 'rewrite' something new.