Scientists have devised a method for ‘writing’ on a surface using molecular holograms and electron waves. The method is demonstrated online in Nature Nanotechnology this week.

Many experiments in nanotechnology involve placing individual atoms or molecules on a surface with a device called a scanning tunnelling microscope (STM). Indeed the power of the STM was famously demonstrated in 1990 when two researchers spelt out IBM with 35 xenon atoms on a nickel surface. It was thought that the need to have enough distance between the atoms or molecules to stop them reacting with each other would limit the amount of information that could be written on a surface.

Hari Manoharan and co-workers show that it is possible to exceed this limit by using the STM to position single molecules on a surface so they form a hologram, rather than using it to write directly on the surface. A conventional hologram uses light waves to store and project three-dimensional images that can be seen by the eye. The molecular hologram, on the other hand, relies on electronic wave functions to create images in two spatial dimensions and one energy dimension that can be 'read' with the STM. Using this hologram, the researchers were able to create and detect objects with features as small as ~0.3 nanometres, allowing them to write letters that occupy only half the area taken up by the smallest letters written directly onto the surface with metal atoms.