Band gaps in jagged and straight graphene nanoribbons tunable by an external electric field.

PublishedJournal ArticleResearch Support, Non-U.S. Gov'tThis is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.Band gap control by an external field is useful in various optical, infrared and THz applications. However, widely tunable band gaps are still not practical due to a variety of reasons. Using the orthogonal tight-binding method for π-electrons, we have investigated the effect of the external electric field on a subclass of monolayer chevron-type graphene nanoribbons that can be referred to as jagged graphene nanoribbons. A classification of these ribbons was proposed and band gaps for applied fields up to the SiO2 breakdown strength (1 V nm(-1)) were calculated. According to the tight-binding model, band gap opening (or closing) takes place for some types of jagged graphene nanoribbons in the external electric field that lies on the plane of the structure and perpendicular to its longitudinal axis. Tunability of the band gap up to 0.6 eV is attainable for narrow ribbons. In the case of jagged ribbons with armchair edges larger jags forming a chevron pattern of the ribbon enhance the controllability of the band gap. For jagged ribbons with zigzag and armchair edges regions of linear and quadratic dependence of the band gap on the external electric field can be found that are useful in devices with controllable modulation of the band gap.Thisworkwas supported by EU FP7 ITNNOTEDEV (through Grant No. FP7-607521); IRSES projects CACOMEL (Grant No. FP7-247007), FAEMCAR (Grant No. FP7-318617) and CANTOR (Grant No. FP7-612285); Graphene Flagship (Grant No. 604391) and the Ministry of Education of the Republic of Belarus (Grant No. 20140773). The authors are very grateful to Prof P Lambin and Prof M Portnoi for their useful advice and Charles Downing for his careful reading of the manuscript

Ultrahard carbon film from epitaxial two-layer graphene

Atomically thin graphene exhibits fascinating mechanical properties, although its hardness and transverse stiffness are inferior to those of diamond. To date, there hasn't been any practical demonstration of the transformation of multi-layer graphene into diamond-like ultra-hard structures. Here we show that at room temperature and after nano-indentation, two-layer graphene on SiC(0001) exhibits a transverse stiffness and hardness comparable to diamond, resisting to perforation with a diamond indenter, and showing a reversible drop in electrical conductivity upon indentation. Density functional theory calculations suggest that upon compression, the two-layer graphene film transforms into a diamond-like film, producing both elastic deformations and sp2-to-sp3 chemical changes. Experiments and calculations show that this reversible phase change is not observed for a single buffer layer on SiC or graphene films thicker than 3 to 5 layers. Indeed, calculations show that whereas in two-layer graphene layer-stacking configuration controls the conformation of the diamond-like film, in a multilayer film it hinders the phase transformation.Comment: Published online on Nature Nanotechnology on December 18, 201

Calling all chemists

Graphene has potentially useful electronic properties but it is difficult to produce and process on large scales. Working with chemically modified forms of graphene-such as graphene oxide-may provide an alternative