If you dump a handful of coins on a table, the surface becomes bumpy. But add more coins, and they spread out into a flat layer on their own. Something similar happens when you deposit ultra-thin films of individual molecules onto a substrate.
At first, islands appear on the surface — molecules cluster together like people in a queue. The film gets rougher and rougher. But at some point, the islands start to merge with each other, and the roughness drops sharply. The film smooths itself out.
The scientists tested this effect with two very different molecules. One is buckminsterfullerene C60, a nearly perfect sphere of 60 carbon atoms. The other is HATCN, a flat molecule shaped like a disk. Despite their different shapes, both films grew the same way: first bumpy, then smooth.
This means the mechanism is universal. It doesn't depend on which molecules you deposit or how fast you do it. So you can predict in advance when the film will become smooth and control its quality in manufacturing.
This behavior of films opens the way to creating nanocoatings with a desired roughness — for example, for screens, sensors, or solar cells.
Buckminsterfullerene C60 is named after the architect Buckminster Fuller, whose geodesic domes resemble the shape of this molecule.
In Arthur C. Clarke's novel "The Fountains of Paradise," a space elevator is made of carbon nanotubes — close relatives of fullerenes.