Modifying the band gap of an armchair graphene nanoribbon by edge bond relaxation

Abstract

The edge bond relaxation is an interesting techniques used to modify the band gap of an armchair graphene nanoribbon (AGNR) which is not possible for the case of a carbon nanotube. In this work, the modification of band gap of an AGNR by edge bond relaxation has been investigated via tight-binding calculation. When edge bond relaxation effects taken into account the carbon-carbon (CC) bond length at the left and right edges is slightly reduced as compared to the CC bond length in the middle of the AGNR as a result the electronic subbands found within their corresponding band structures shifts either upward or downward that leads to the change in their band gap due to the change in positions of both the conduction band minimum and the valence band maximum. The results show that without edge bond relaxation the AGNR exhibits direct band gap semiconductor behavior with a very small band gap of a u-v = 3 m + 2 family close to metallic property. The results further show that with edge bond relaxation the all AGNRs maintain their superior direct band gap semiconducting properties with band gap of the u-v = 3 m + 1 and u-v = 3 m + 2 families increases while the band gap of a u-v = 3 m family decreases as compared to the without edge bond relaxation for similar chirality values (u, v). Finally, it has been observed that the modification in band gap of an AGNR by edge bond relaxation opens up their availability for designing improved version of a good field-effect transistor and due to their direct band gap they are suitable nanostructured material for light-emitting diodes, lasers, and solar cells.