GNR band structure for armchair type. Tight binding calculations show that armchair type can be semiconducting or metallic depending on width (chirality).
Tiny nanoribbons of carbon could be used to make a magnetic field sensor for novel electronic devices
Researchers in Singapore have designed an electronic switch that responds to changes in a magnetic field. The device relies on graphene, a strong and flexible electricity-conducting layer of carbon atoms arranged in a honeycomb pattern.
Seng Ghee Tan of the A*STAR Data Storage Institute, along with colleagues at the National University of Singapore, used theoretical models to predict the properties of their proposed device, known as a magnetic field-effect transistor.
The transistor is based on two nanoribbons of graphene, each just a few tens of nanometers wide, which are joined end to end. The atoms along the edges of these nanoribbons are arranged in an ‘armchair’ configuration — a pattern that resembles the indented battlements of castle walls. If these edges were in a zigzag pattern, however, the material would have different electrical properties.
One of the nanoribbons in the team’s transistor acts as a metallic conductor that allows electrons to flow freely; the other, slightly wider, nanoribbon is a semiconductor. Under normal conditions, electrons cannot travel from one nanoribbon to the other because their quantum wavefunctions — the probability of where electrons are found within the materials — do not overlap.
A magnetic field, however, warps the distribution of electrons, changing their wavefunctions until they overlap and allowing current to flow from one nanoribbon to the other. Using an external field to change the electrical resistance of a conductor in this way is known as a magnetoresistance effect.
The team calculated how electrons would travel in the nanoribbons under the influence of a 10-tesla magnetic field — the rough equivalent of that produced by a large superconducting magnet — at a range of different temperatures.
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