Raised dots on a page can be carefully arranged to convey a message to a blind reader. Now scientists have borrowed the Braille strategy and applied it to molecules. Devices employing the technique, described in a paper published in the current issue of the journal Science, could store up to 100 gigabits of data per square inch.

Many molecular systems can store information because they have two different, yet equally stable configurations and can be reliably switched between the two. Magnifying these effects to larger systems, however, can be extremely difficult. In the new design, Massimiliano Cavallini of the Consiglio Nazionale delle Ricerche-ISMN in Bologna, Italy, and his colleagues exploited a class of compounds know as rotaxanes. These molecules are shaped like miniature barbells with rings surrounding thin handles. "Their architecture, analogous to an abacus, suggests that they could be used as switchable components for artificial machines that function through mechanical motion at the molecular level," the scientists note.

The team grew thin films of three types of molecules and examined their surfaces with the probe of an atomic force microscope. Initially, the surface remained smooth, but the researchers found that when they increased the applied pressure, the rings in each row formed a predictable pattern of dots that could encode data. According to the report, the number of dots was directly related to the length of microscope's scan, whereas the spacing between the dots was determined by the thickness of the film. "Our approach enables the writing of multiple dots simultaneously," the authors conclude. "This could make it suitable for scaling up to a lithography based on multiple sources of perturbation, such as a stamp."