Atomic hard disk could store every book ever written on postage stamp

A hard disk that uses individual chlorine atoms to store data could pave the way for miniature devices with significantly larger capacities than current technology allows.

A team at the Kavli Institute of Nanoscience at Delft University in the Netherlands developed a one kilobyte (8,000 bits) memory chip, where each bit is represented by the position of one single chlorine atom.

"In theory, this storage density would allow all books ever created by humans to be written on a single post stamp," says lead-scientist Sander Otte.

With modern society creating more than a billion gigabytes of new data every day, it is increasingly important that each bit occupies as little space as possible.

The atomic storage medium has reached a density of 500 Terabits per square inch (Tbpsi), 500 times better than the best commercial hard disk currently available.

The team 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," Otte explains. "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. 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. This makes the technique much more stable than methods with loose atoms and more suitable for data storage.

The researchers from Delft organised 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.

Inspired by the pixelated square barcodes (QR codes) often used to scan tickets for airplanes and concerts, these markers work like miniature QR codes that carry information about the precise location of the block on the copper layer.

The code also indicates if a block is damaged e.g. 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.

Although the new approach offers excellent stability and scalability, it is not expected to be used in data centres for some time.

"In its current form, the memory can operate only in very clean vacuum conditions and at liquid nitrogen temperature (77 K),” Otte said.

“So the actual storage of data on an atomic scale is still some way off. But through this achievement we have certainly come a big step closer."

In April, a magnet the size of a single atom was revealed by Swiss researchers that boasted unprecedented levels of stability and was heralded as a major milestone in the ongoing miniaturisation of data storage devices. 

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