Chiral graphene nanoribbon inside a carbon nanotube: ab initio study Irina V. Lebedeva, * ab Andrey M. Popov, c Andrey A. Knizhnik, ab Andrei N. Khlobystov d and Boris V. Potapkin ab Received 17th January 2012, Accepted 1st May 2012 DOI: 10.1039/c2nr30144j The dispersion-corrected density functional theory (DFT-D) is applied for investigation of structure and electronic properties of a sulfur-terminated graphene nanoribbon (S-GNR) encapsulated in a carbon nanotube. Two mechanisms of accommodation of the GNR in the carbon nanotube, distortion of the nanotube cross-section into an elliptic shape accompanied by bending of the GNR and transformation of the GNR to a helical conformation, are analyzed. Three types of elastic distortions of the nanotube and encapsulated GNR are revealed depending on the ratio of the diameter of the nanotube cavity to the GNR width. Helical states of the GNR are shown to be stabilized by the van der Waals attraction of sulfur atoms at neighbouring edges of adjacent turns of the GNR. The results of calculations are correlated with the experimental observations for the S-GNR synthesized recently inside the carbon nanotube. The hybrid DFT calculations of band structures of zigzag GNRs terminated with different atoms demonstrate that as opposed to O- and H-GNRs, the S-GNR is metallic even when deformed inside carbon nanotubes. Possible applications of GNRs encapsulated in carbon nanotubes are discussed. 1. Introduction The new carbon nanostructure, graphene, 1 is currently receiving significant attention because of the unique physical properties it exhibits. Nevertheless, the absence of an electronic band gap in this material remains one of the main obstacles hindering its application in electronic devices. One of the most effective solutions for introducing an energy gap between the conduction and valence bands of graphene is to shape it into strips of fixed width – graphene nanoribbons (GNRs). 2–8 Formation of GNRs with well-defined, atomically smooth edges is essential for controlling their electronic properties. However, as discovered very recently, this is possible only by assembly of these nano- structures inside carbon nanotubes (CNTs). 9 Electronic properties of GNRs are sensitive to their confor- mation. For example, it was demonstrated that twisting (Fig. 1a) induces changes in band gaps of GNRs. 10–12 Such a twisting was observed for hydrogen-terminated GNRs (H-GNRs) synthesized recently inside single-walled nanotubes (SWNTs) in the case when the GNRs are loose inside the nanotubes (for the ratio of the diameter D c of the nanotube cavity to the GNR width w in the range D c /w ¼ 1.7–4.0). 13 However, structures consisting of wide GNRs encapsulated in narrow CNTs, as in the experiment in ref. 9 (D c /w z 1.3), might be more interesting for practical applications. In this case, the GNR conformation is determined by the shape of the nanotube cavity and, therefore, the GNR conformation and electronic properties can be controlled by deformation of the nanotube walls. Nanotubes encapsulating GNRs with tunable electronic properties hold great promise for use in single-molecule nanoelectronic devices. The chemically inert nanotube walls make it possible to use such nanoelectronic devices under ambient conditions (e.g., in air) and even in aggressive environments. The knowledge of precise relationships Fig. 1 (a) Structure of the H-GNR twisted around its axis which was studied in ref. 10–12. Schematic representation of two mechanisms of accommodation of a S-ZGNR in a SWNT: (b) distortion of the SWNT cross-section into an elliptic shape and bending of the GNR and (c) transformation of the GNR to a helical conformation. Left: side views; right: on-end views. Sulfur, carbon and hydrogen atoms are coloured yellow, gray and blue, respectively. a National Research Centre ‘‘Kurchatov Institute’’, Kurchatov Square 1, Moscow 123182, Russia b Kintech Lab Ltd., Kurchatov Square 1, Moscow 123182, Russia. E-mail: lebedeva@kintechlab.com; knizhnik@kintechlab.com; Fax: +74991969992; Tel: +74991969992 c Institute of Spectroscopy of Russian Academy of Sciences, Fizicheskaya Street 5, Troitsk, Moscow Region 142190, Russia. E-mail: am-popov@ isan.troitsk.ru d School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK 4522 | Nanoscale, 2012, 4, 4522–4529 This journal is ª The Royal Society of Chemistry 2012 Dynamic Article Links C < Nanoscale Cite this: Nanoscale, 2012, 4, 4522 www.rsc.org/nanoscale PAPER