The cutting edge of graphene edge cutting
Using a scanning tunnelling microscope, resolving at a sub-nanometre scale, researchers in the US have taken a detailed look at the edges of graphene nanoribbons (GNR). The researchers aim was to discover how the angle at which the GNR was cut affects the properties of the ribbon’s edges.
Since graphene was discovered, scientists have speculated about how the edges might behave; the properties they would bestow on nanoribbons of the material and how those might differ from sheet graphene. In particular, scientists predicted that GNR would have a band gap – a property missing in sheet graphene – which would allow transistors made from the material to be properly switched off.
Lead researcher Michael Crommie (of Berkeley Lab’s Materials Sciences Division (MSD) and UC Berkeley’s Physics Division) is quoted in the university’s press announcement that this is the first time anyone has been able to see the atomic-scale structure and at the same time measure its electronic properties within nanometres of the edge.
The first step is to get hold of a nicely edged nano ribbon, and to do that, the researchers turned to Hongjie Dai of Stanford University’s Department of Chemistry and Laboratory for Advanced Materials. He suggested unzipping a carbon nanotube.
A nanotube can be wrapped at any angle, providing various degrees of chirality, or handedness, the researchers say. By chemically unzipping the tubes straight down their length, the researchers could create a variety of chirality vectors, where the 'zip' cuts across the hexagons of carbon anything from vertically or horizontally. And in each case, the properties are very different.
Crommie adds: "The optimist says, 'Wow, look at all the ways we can control these states – this might allow a whole new technology!' The pessimist says, 'Uh-oh, look at all the things that can disturb a nanoribbon’s behavior – how are we ever going to achieve reproducibility on the atomic scale?'"
The work is published in Nature, Physics May 8th advance online edition here.