The 1 kilobyte device has an information storage density that is two to three orders of magnitude beyond current hard disk or flash technology. With each bit of data represented by the position of a single chlorine atom, the team was able to reach a density of 500 Terabits per square inch.
‘You would need just the area of a postage stamp to write out all books ever written,’ said study senior author Sander Otte, a physicist at the Delft University of Technology’s (TU Delft) Kavli Institute of Nanoscience in the Netherlands. Or, to take another measurement, the research team estimated that if they created a cube 100 microns wide – about the same diameter as the average human hair – it could store the entire contents of the US Library of Congress.
The scientists created their atomic memory device using a scanning tunnelling microscope (STM), which uses an extremely sharp needle to probe the atoms on the surface one by one. STM probes can not only detect atoms, but also nudge them around.
Computers represent data as 1s and 0s – binary digits known as bits that they express by flicking tiny, switch-like transistors either on or off. The new atomic memory device represents each bit as two possible locations on a copper surface; a chlorine atom can slide back and forth between these two positions, the researchers explained.
‘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,’ Otte commented. ‘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.’
The bits are separated from one another by rows of other chlorine atoms. These rows could keep the bits in place for more than 40 hours, the scientists found. This system of packing atoms together is far more stable and reliable than atomic memory strategies that employ loose atoms, the researchers said. As a result, it is far more suitable for practical data storage applications.
These atoms were organised into 127 blocks of 64 bits. Each block was labelled with a marker of holes. These markers are similar to the QR codes now often used in ads and tickets. These markers can label the precise location of each block on the copper surface. The markers can also label a block as damaged; perhaps this damage was caused by some contaminant or flaw in the copper surface — about 12 % of blocks are not suitable for data storage because of such problems, according to the researchers. All in all, this orderly system of markers could help atomic memory scale up to very large sizes, even if the copper surface the data is encoded on is not entirely perfect, they said.
As a proof of principle, the team encoded a section of a famous lecture called ‘There’s plenty of room at the bottom’ by the famous physicist Richard Feynman on an area 100 nanometres wide.
However, despite its future promise, the approach is not ready for full commercialisation yet. Stable information storage could only be demonstrated at a temperature of 77 Kelvin (-196C) and the speed of single write and read processes is still slow – on the scale of minutes.
Although a huge achievement, for Otte the great promise of atomic memory simply demonstrates how well scientists can now engineer devices on the level of atoms. ‘I cannot, at this point, foresee where this will lead, but I am convinced that it will be much more exciting than just data storage,’ he said.
The research has been published in the journal ‘Nature Nanotechnology’