Researchers from Delft University of Technology in the Netherlands have created a rewritable data-storage device capable of storing information at the level of single atoms representing single bits of information.
The technology, which is described in the current issue of Nature Nanotechnology, is capable of packing data as dense as 500 terabytes per square inch. Theoretically, the device could store the entire contents of the US Library of Congress within a 0.1-mm-wide cube—though the proof-of-concept demonstrated by the group topped out at 1 kilobyte.
Physicists have been capable of manipulating single atoms for 25 years, but there are several problems that preclude easily implementing atomic-scale memory. For one thing, atoms don't tend to sit still very well given the thermal perturbations found at most reasonable temperatures. And then there is the problem of finding a suitable material and process that allows for the detection and manipulation of the atoms.
Said manipulation is done here using a scanning tunneling microscope (STM), an invaluable tool for imaging and tweaking surfaces at atomic scales. In 1990, physicist Don Eigler famously spelled out the letters "IBM" with 35 xenon atoms via an STM (top), but the Delft group achieves their information storage in sort of an inverse manner. Rather than arranging atoms in various ways, their storage grid is based on atomic vacancies—spaces within a layer where atoms should be.
"The overall layout is a 12 × 12 array of rectangular blocks, each block consisting of a grid of dark spots whose positions vary like the beads on an eight-stringed abacus," explains Steven Erwin, a computational materials scientist at the Naval Research Laboratory, in a Nature commentary. "In contrast to the xenon atoms of 'IBM', these spots are not atoms but rather their absence—that is, vacancies in a layer of chlorine atoms deposited on a copper substrate. The vacancies can be easily and reproducibly manipulated by moving one of the four adjacent atoms using an STM tip."
The vacancy method has a couple of key advantages. One, because the vacancies are relatively stable, the storage device doesn't have to be kept quite as cold—rather than liquid helium (-210°C), we "only" need liquid nitrogen (-196°C). Two, by scooting around atomic vacancies rather than picking up individual atoms, the physicists were able to achieve better than 99 percent reliability. Moreover, the vacancies can be manipulated in a completely "hands-off" or automated fashion.
"After scanning the area, the positions of all vacancies are determined via image recognition," the Delft paper explains. "Next, a pathfinding algorithm is used to calculate the building sequence, guiding the vacancies to their respective final positions. The markers for adjacent blocks are built automatically as part of the construction, and leftover vacancies are swept to the side to be used in future blocks. Automated construction of a complete block takes on the order of 10 minutes."
Of course, data centers generally cruise at temperatures considerably higher than -196°C. The need for liquid nitrogen is a significant barrier, to say the least. There is also the issue of speed: reading a block of memory takes about 10 minutes. The Delft group notes, however, that given the maximum bandwidth of STM electronics, it should theoretically be possible to boost that to 1 megabit per second.