Credit: © 2006 National Academy of Sciences USA

The bottom-up fabrication of materials relies on the assembly of molecules into large, ordered structures. Although molecules can be designed to self-assemble into organized structures, achieving this in technologically relevant environments, such as on surfaces or in thin films, has been difficult.

Researchers at the Instituto per lo Studio dei Materiali Nanostrutturati in Italy and the University of Edinburgh in the UK can now trigger molecules to self-assemble on a surface, and form structures with long-range order, by using an atomic force microscope tip. Fabio Biscarini and colleagues1 deposited a thin film of rotaxanes — mechanically interlocked molecules in which a ring component is trapped on a dumbbell-shaped one — on a graphite surface and scanned an atomic force microscope tip across the film. The mechanical stimulus from the tip triggered the rotaxanes to self-organize into regularly spaced dots that could coalesce to form lines under the right conditions.

The researchers found that film thickness determined the size and spacing of the dots. Interestingly, this ability to self-assemble was not seen with other molecules and it worked only for certain types of rotaxanes. It was proposed that the mechanical perturbation from the tip provides energy for the molecules to reorganize themselves. This phenomenon could be exploited to produce dense arrays of organized dots for information storage applications.