Writing the world’s smallest letters

Keeping with our theme of nanotechnology this week, researchers at Stanford University in the States have managed to write the smallest letters ever - assembled from subatomic particles just 0.3 nanometres in size. The researchers are particularly pleased with their achievement, because it was Stanford scientists that first created the world's smallest writing in 1985, but lost the record in 1990 to IBM, when they famously arranged xenon atoms to spell out the company's name. Now they have it back.

But how did they do it? The researchers encoded the letters "S" and "U" (standing for Stanford University) by using the interference pattern of electron waves on the surface of a film of copper. The technique actually projects a tiny hologram of the letters, which can only be seen using a very powerful microscope.

Writing about their work in the journalNature Nanotechnology, the Stanford team's letters are more than four times smaller than the IBM initials, and were created using a scanning tunnelling microscope, which can be used to push atoms around. The scientists used it to put individual molecules of carbon monoxide in a special pattern on a film of copper the size of a fingernail.

Electrons are constantly whizzing around on the copper, because it is a metal. And because electrons can act as waves, as well as the more traditional view that they are particles, the electron waves get shaped by the carbon monoxide, and interfere with each other like ripples in a pond. These interference patterns depend on the position of the carbon monoxide molecules on the copper surface. So eventually they create a consistent pattern that can be read, like a molecular hologram.

It all sounds quite nerdy, but the technique could be very important for the future of computing, as it would enable information to be stored at a very high density in small chips. For example, the researchers could create different holograms on the same chip by using different electron wavelengths, increasing the amount of information that can be stored, and pushing it beyond current boundaries.