As the need for data storage increases, memory devices are becoming ever smaller and single bits of data need to occupy less and less space. Now, a team of researchers led by Sander Otte has built a memory of 1 kilobyte (8000 bits) in which each bit is represented by the position of just one single chlorine atom vacancy.

Making use of the self-assembly of chlorine atoms on a copper surface, researchers can assemble arrays of atoms by positioning atoms or molecules evaporated onto a flat metal surface, such as the (111) crystal surface of copper. In their experiments, Otte and colleagues made use of the self-assembly of chlorine atoms on a copper surface. Here, chorine atoms form a flat, 2D lattice on the copper and the researchers are able to probe the atoms one by one using the sharp tip of a scanning tunnelling microscope (STM) probe. They are also able to drag the atoms around.

Like a "sliding puzzle"

The array looks like a sliding puzzle, explains Otte. Every bit consists of two positions on the surface of the copper atoms, and one chlorine atom that we can slide back and forth between these two positions. If the chlorine atom is in the top position, there is a hole beneath it and we call this position “1”. If the hole is in the top position and thr chlorine atom is therefore on the bottom, then the bit is a “0”.

Since other chlorine atoms surround the chlorine atoms, except near the holes, they hold each other in place, he adds. That is why our method with holes is much more stable than methods with loose atoms and more suitable for data storage.

As a proof of principle, the team encoded a section of Richard Feynman’s famous "There's plenty of room at the bottom" lecture on an area 100 nanometres wide (see figure).

Forming the vacancies

The team, reporting its work in Nature Nanotechnology doi:10.1038/nnano.2016.131, produced the chlorine vacancies by stopping the self-assembly process before a complete atomic layer of chlorine forms on the copper surface. In this way, they created a surface full of chlorine vacancies that can then be assembled into blocks – of 8 bytes (64 bits) in this case.

Although the new approach is promising, there is still a long way to go says Otte. For one, reading and writing speeds using the STM are slow – as long as two minutes for reading a block and about 10 minutes for writing one. And the memory only works at liquid nitrogen temperatures. Nevertheless it is important to recognize the significance of this accomplishment, says Steven Erwin in a related Nature News & Views article. For example, the areal density of about 500 terabits per square inch “is two to three orders of magnitude beyond current hard disk or flash technology. An advance of this size is remarkable to say the least.”