An international group of researchers from Spain, Portugal and the Netherlands has demonstrated an atomic-scale memory device with a storage density of 502 Terabits per square inch (Tbpsi), outperforming state-of-the-art hard disk drives by three orders of magnitude.

“In theory, this storage density would allow all books ever created by humans to be written on a single post stamp,” said team leader Dr. Sander Otte, from the Kavli Institute of Nanoscience at the Delft University of Technology.

Dr. Otte and co-authors used a scanning tunneling microscope (STM), in which a sharp needle probes the atoms of a surface, one by one. With these probes scientists cannot only see the atoms but they can also use them to push the atoms around.

“You could compare it to a sliding puzzle. Every bit consists of two positions on a surface of copper atoms, and one chlorine atom that we can slide back and forth between these two positions,” Dr. Otte explained.

“If the chlorine atom is in the top position, there is a hole beneath it — we call this a 1.”

“If the hole is in the top position and the chlorine atom is therefore on the bottom, then the bit is a 0.”

“Because the chlorine atoms are surrounded by other chlorine atoms, except near the holes, they keep each other in place. That is why this method with holes is much more stable than methods with loose atoms and more suitable for data storage.”

The researchers organized their memory in blocks of 8 bytes (64 bits).

Each block has a marker, made of the same type of ‘holes’ as the raster of chlorine atoms.

These markers work like miniature QR codes that carry information about the precise location of the block on the copper layer.

The code will also indicate if a block is damaged, for instance due to some local contaminant or an error in the surface.

This allows the memory to be scaled up easily to very big sizes, even if the copper surface is not entirely perfect.

“In its current form the memory can operate only in very clean vacuum conditions and at liquid nitrogen temperature (77 degrees Kelvin), so the actual storage of data on an atomic scale is still some way off,” Dr. Otte said.

“But through this achievement we have certainly moved a big step closer.”

The team’s results were published this week in the journal Nature Nanotechnology.

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F.E. Kalff et al. A kilobyte rewritable atomic memory. Nature Nanotechnology, published online July 18, 2016; doi: 10.1038/nnano.2016.131