Conventional photolithography, used to make chips, hits a fundamental limit: light cannot draw features smaller than its wavelength. Here, they took a different route. First, they made sparse vertical ridges of oxide, then deposited layers of aluminum oxide, each one atom thick, onto them. Each layer also grew on the sides of the ridges, narrowing the gaps between them — like snow piling up on branches, gradually closing the openings.
This produced a comb with teeth spaced 1.75 nanometers apart. For comparison, a DNA strand is about 2 nanometers thick. The gaps between the teeth act as tiny gates: if you place a sheet of graphene under the comb, these gates begin to control the movement of electrons within it. In the experiment, additional peaks appeared in the conductivity plot — a sign that electrons started to feel the periodicity of the lattice, like waves reflecting off a picket fence.
Such a fine comb is useful not only for electronics. Light with very short wavelengths, such as X-rays, also interacts with periodic structures. This means it could be used to make mirrors and lenses for hard radiation, which are nearly impossible to produce today. It could also control polaritons — hybrid particles of light and matter — which would be valuable for new lasers and sensors.
For now, this is just a proof of concept: the scientists showed the method works and tested it on graphene. But the very idea — turning layer-by-layer deposition into a tool for ultra-fine engraving — opens the way to mass production of nanostructures that previously existed only in calculations.
A gap of 1.75 nanometers is roughly 10 aluminum atoms laid out in a row.
In Neal Stephenson's novel 'The Diamond Age,' nanotechnology allows building things atom by atom — the new platform takes a step in the same direction, but from the top down, from a large workpiece to tiny features.