Nanowires can emit, concentrate and absorb light and so are used to add optical functionalities to electronic chips. They can be used in solar panels to improve how sunlight is converted into electrical energy, as well as allowing lasers directly on silicon chips and to integrate single-photon emitters for coding purposes. However, up until now, growing nanowires reliably on silicon sunstrates has been a major challenge.
The tam at the lab, run by Anna Fontcuberta i Morral, together with colleagues from MIT and the IOFFE Institute, developed a new model of what happens at the onset of nanowire growth, which goes against currently accepted theories. Their work has been published in Nature Communications.
"We think that this discovery will make it possible to realistically integrate a series of nanowires on silicon substrates," said Fontcuberta i Morral. "Up to now, these nanowires had to be grown individually, and the process couldn't be reproduced."
The standard process for producing nanowires is to make tiny holes in silicon monoxide and fill them with a nanodrop of liquid gallium. This substance then solidifies when it comes into contact with arsenic. But with this process, the substance tends to harden at the corners of the nanoholes, which means that the angle at which the nanowires will grow can’t be predicted. The search was on for a way to produce homogeneous nanowires and control their position.
Research aimed at controlling the production process has tended to focus on the diameter of the hole. The EPFL team has shown that by altering the diameter-to-height ratio of the hole, they can perfectly control how the nanowires grow. At the right ratio, the substance will solidify in a ring around the edge of the hole, which prevents the nanowires from growing at a non-perpendicular angle. And the researchers’ process should work for all types of nanowires. This new production technique will be a boon for nanowire research, and further samples should soon be developed.