Tuesday, July 19, 2016

Atomic Level Data Storage.

This brief commentary will appear in the next issue of the journal Science Progress of which I am an editor. Meanwhile here is a preview of a fascinating development in computing technology.

There is a growing trend to store more of our data in large data centres using cloud computing resources. Indeed, the amount of data produced by humans increases by more than one billion gigabytes per day. Thus, it is necessary to construct continually more data centres, the running of which consumes large amounts of energy. In order to maintain the capacity of storage media in pace with demand, it is necessary to reduce the amount of space that each piece of information occupies. However, there are limits to how small we can go, due to the roughness of the materials used for data storage, meaning that thousands of atoms are necessary to specify each piece of information. However, if the smoothness of the material could be honed down to the level of individual atoms, it might be possible for each data element to consist of just a single atom. Researchers at Delft University of Technology have achieved precisely this, by placing chlorine atoms on a copper surface, which form a perfect square grid. At particular locations on the grid, there is a chlorine atom missing, leaving a hole. Using the tip of a scanning tunnelling electron microscope (STEM), it is possible to move another chlorine atom into the hole from elsewhere in the grid. A good analogy is with a sliding puzzle, in which small square elements are moved around with a finger, so that the hole is effectively moved around the grid.

Multiple holes can be moved around in precise arrangements to form “bits” (101010, etc), “letters” (ABC, etc), then “words”, to describe
eventually an entire text. The Delft researchers have managed to construct an entire one kilobyte, containing 8,000 atomic bits, where each bit is represented by the position of a single chlorine atom. Although there have been previous reports of simple logos, e.g. “IBM” and “2000”, being “written” by towing around atoms molecules on surfaces, this is by far the largest atomically assembled architecture so constructed to date. In addition, the memory also contains atomic-scale markers which render it possible to steer the STM tip through the large array of bits. These markers are of particular importance, since they both mark the start and end of each line, and can furthermore identify the presence of contamination or a crystal defect in a sector of the grid which impede its facility for data storage. Such features are essential if the technology is to be scaled-up further.

The areal storage density of the memory is 502 Terabits per square inch, which exceeds existing state-of-the-art hard-disk drives by a factor of three orders of magnitude. To place this storage density in context, the text of all the books ever written by humans could be written on the surface the area of a postage stamp. In its present form, the memory needs to be kept in an ultra-clean, vacuum-environment and at low temperatures (< 77 K). It is hoped that the relative robustness of the material will enable it to be used outside the laboratory and in practical applications.

Kalff, F.E. et al. (2016) Nature Nanotechnology,
Published online 18 July 2016.  doi:10.1038/nnano.2016.131

1 comment:

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