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Graphene nanoribbon

Graphene has no gap between its valence and conduction bands which is essential for electronics applications because it allows a material to switch the flow of electrons on and off. But a band gap can be introduced into graphene by making extremely narrow ribbons. For example, dense arrays of 10 nm wide graphene nanoribbons can have a band gap of about 0.2 eV. Graphene nanoribbons (GNRs), are strips of graphene with ultra-thin width (<50 b="b">
By using small molecule precursors, scientists have found a way to precisely build graphene nanoribbons and make them in different shapes. Most routes to make nano-graphene are top-down - starting from a bulk material and breaking it up which has been tricky to make nano-sized ribbons of graphene with a defined structure of a size that would be useful in nanoelectronics. Width controlled GNRs can be produced via graphite nanotomy process shown by Berry group, where sharp diamond knife application on graphite produces graphite nanoblocks, which are exfoliated to produce GNRs. GNRs can also be produced by unzipping or cutting open nanotubes. In one such method by Tour group multi-walled carbon nanotubes were unzipped in solution by action of potassium permanganate and sulfuric acid. In another method GNRs were produced by plasma etching of nanotubes partly embedded in a polymer film. Depending on the precursor used, the scientists can make either linear ribbons or zig-zags. Because the ribbons are made by building them from the bottom up, they are all identical in size and shape. More recently, graphene nanoribbons have been grown onto silicon carbide (SiC) substrates using ion implantation followed by vacuum or laser annealing.
Narrowest nanoribbon
Researchers at IBM and the University of California-Riverside have succeeded in making the narrowest ever nanoribbon arrays of epitaxial graphene on a silicon carbide wafer. Each nanoribbon has a width of just 10 nm, size which is almost impossible to achieve using conventional top-down lithography alone.
Researchers make a large number of GNRs in parallel covering about 50% of the finished device channel area to get integrated circuits based on GNRs with the required high current densities.
The researchers claim that GNRs can be produced with well controlled dimensions having smooth edges to get exceptional electronic transport properties. The process developed by the researchers to make the GNR arrays is a hybrid one consisting of a top-down e-beam lithography step that can also be performed using standard photolithography with an appropriate mask and a bottom-up self-assembly step involving a block copolymer template comprising alternating lamellae of the polymers PS and PMMA which is Poly methyl methacrylate, a transparent thermoplastic.

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