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. Over the next year, Willis and his collaborators in Pennsylvania plan to build prototype rectennas and begin testing their efficiency.
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For years, scientists have studied the potential benefits of a new branch of solar energy technology that relies on incredibly small nanosized antenna arrays that are theoretically capable of harvesting more than 70 percent of the sun’s electromagnetic radiation and simultaneously converting it into usable electric power.
The potential breakthrough lies in a novel fabrication process called selective area atomic layer deposition (ALD) that was developed by Willis, an associate professor of chemical and biomolecular engineering and the previous director of UConn’s Chemical Engineering Program.
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 nanosized gap gives energized electrons on the rectenna just enough time to tunnel to the opposite electrode before their electrical current reverses and they try to go back. The triangular tip of the rectenna makes it hard for the electrons to reverse direction, thus capturing the energy and rectifying it to a unidirectional current.