Attempts with current nanofabrication standards such as lithography and plasma etching, however, have left rough edges to the nanoribbons that affect their performance. Until now, these structures have been impossible to achieve because the rough, non-crystalline edges of the graphene, resulting from current state-of-the-art nanolithography techniques, are considered the limiting factor to attaining useful performance from nanoscale graphene devices. Even atomic-scale flaws would derail electrical conductivity of any graphene transistors. Johnson's technique, employing hot iron nanoparticles to carve out patterns in graphene sheets, appears to be the first detailed example of such precise fabrication.
To create these ribbons, researchers deposited graphene onto a silicon substrate, coated them in iron nitrate and heated them to 900 C. At that temperature, the iron forms particles with diameters of about 15 nm, spreads across the surface of the substrate and etches away trenches in the graphene sheets.
By identifying areas where two iron nanoparticles carved parallel tracks like skis in fresh snow, researchers managed to isolate nanoribbons as narrow as 15 nm and as much as a few micrometers long. The nanoparticles travel predominantly along a single direction, although why this was so is a question for another study. However, scientists also observed the existence of other paths of nanoparticles, at angles of 30 and 60, suggesting possibly that the motion of the iron nanoparticles and hence the etching is related to the atomic structure of graphene, a honeycomb shape employing those measurements. This natural phenomena could be used in the future to fabricate devices and circuits with those required angles.
|Contact: Jordan Reese|
University of Pennsylvania