Still in development, nano-antennas built with atomic layer deposition hold promise for replacing semiconductor solar panels.

A novel fabrication technique developed by UConn engineering professor Brian Willis could provide the breakthrough technology scientists have been looking for to vastly improve today's solar energy systems.

The nano-antennas -- known as "rectennas" because of their ability to both absorb and rectify solar energy from alternating current to direct current -- must be capable of operating at the speed of visible light and be built in such a way that their core pair of electrodes is a mere 1 or 2 nanometers apart, a distance of approximately one millionth of a millimeter, or 30,000 times smaller than the diameter of human hair. The potential breakthrough lies in a novel fabrication process called selective area atomic layer deposition (ALD)...

It is through atomic layer deposition that scientists can finally fabricate a working rectenna device. In a rectenna device, one of the two interior electrodes must have a sharp tip, similar to the point of a triangle. The secret is getting the tip of that electrode within one or two nanometers of the opposite electrode, something similar to holding the point of a needle to the plane of a wall. Before the advent of ALD, existing lithographic fabrication techniques had been unable to create such a small space within a working electrical diode. Using sophisticated electronic equipment such as electron guns, the closest scientists could get was about 10 times the required separation. Through atomic layer deposition, Willis has shown he is able to precisely coat the tip of the rectenna with layers of individual copper atoms until a gap of about 1.5 nanometers is achieved. The process is self-limiting and stops at 1.5 nanometer separation.

The size of the gap is critical because it creates an ultra-fast tunnel junction between the rectenna's two electrodes, allowing a maximum transfer of electricity.

The rectenna devices don't rely on a band gap and may be tuned to harvest light over the whole solar spectrum, creating maximum efficiency.

Over the next year, Willis and his collaborators in Pennsylvania plan to build prototype rectennas and begin testing their efficiency."We've already made a first version of the device," says Willis. "Now we're looking for ways to modify the rectenna so it tunes into frequencies better.