Narayan and colleagues used a novel vapor deposition technique to grow precisely aligned nanodots out of nickel. The technique, called domain-matching epitaxy, involves depositing a very thin layer of titanium nitride onto a substrate that serves as a template for the nanodots. The titanium nitride forms single crystal lattices upon which the nanodots are grown. The size of the dots and the spacing between the nanodots can be controlled by varying the growth conditions, such as the temperature.
Finding the right material was crucial, says Narayan. “We needed a metallic material that was nonmagnetic,” he says. This ensures that the templates don’t interfere with the magnetic properties of the nanodots. The technique could be used to create regular arrays of billions of nanodots.
“There is a difficulty in controlling both the size and position of the nanodots,” says Russell Cowburn a professor of nanotetchnology at Imperial College London. “Controlling this would be a huge advantage,” he says.
But Cowburn adds that growing nanodots is only part of the challenge. Making them thermally stable and finding ways to read and write magnetic information are significant challenges, he says.
For nanodot memory to be competitive, it will have to be cheap as well as dense, says Cowburn. In terms of bits per dollar, magnetic hard drives are still the cheapest form of computer memory–about 50 times cheaper than flash.
Currently, the nickel nanodots require low temperatures to function, but Narayan is working on making them out of iron-platinum, which should let them operate at room temperature.