Structural and electronic properties of strained graphene nanoribbons modified by molecules
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Structural and electronic properties of strained graphene nanoribbons modified by molecules T. Urakawa and K. Shintani Department of Mechanical Engineering and Intelligent Systems, University of ElectroCommunications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan ABSTRACT The structural and electronic properties of graphene nanoribbons (GNRs) modified by H, CO, and NH3 molecules at their edges under uniaxial strain is investigated by means of first principles calculations. It is found the bond length of the reconstructed edge of a H-terminated GNR modified by CO is larger than those of a bare GNR, a H-terminated GNR, and a Hterminated GNR modified by NH3. It is also found the band gaps of a H-terminated GNR and a H-terminated GNR modified by CO are twice the gap of a bare GNR, and the band gaps of a bare GNR and a H-terminated GNR increase with the increase of imposed strain. INTRODUCTION Graphene has attracted much attention of researchers since its synthesis by Novoselov et al. [1]. It is expected graphene will overcome the limitations of conventional materials such as carbon nanotubes, silicon, etc. For example, it was shown experimentally that graphene can be excellent chemical sensors [2]. From graphene, GNRs were also fabricated via lithography [3]. GNRs are quasi-one-dimensional materials, and their long edges are so reactive that they can easily be modified by atoms and molecules. Accordingly, GNRs are more suited for sensing gas molecules than graphene itself. Adsorption of gas molecules such as CO, NO, NO2, O2, N2, CO2, and NH3 on GNRs was investigated by Huang et al. [4]. Using density functional theory (DFT) calculation, they showed the electronic and transport properties of GNRs with armchair edges are sensitive to adsorption of NH3 whereas the other gas molecules have little effect on their properties. Hence, it was suggested that NH3 molecules can be detected out of the other molecules via GNR-based sensors. Furthermore, Wu et al. [5] investigated zigzag edged GNRs modified by OH and F atoms. They concluded both the GNRs can be converted to be half-metals, and the electronic behavior of the chemically modified GNRs resembles that of not chemically but structurally modified GNRs. Stimulated by the study of Huang et al., we in this paper investigate whether gas molecules can be detected via armchair edged GNRs. DFT calculations using PHASE code [6] yield the optimized structures of GNRs after adsorption of gas molecules under imposed strain. The optimized structures, density of states (DOS), and charge density distributions are calculated. SIMULATION METHOD Figure 1 shows supercells of GNRs for calculation; (a) indicates the way of cutting a supercell out of, e.g., a H-terminated GNR, (b) is a supercell for a bare GNR, (c) for a Hterminated GNR, (d) for a H-terminated GNR modified by CO, and (e) for a H-terminated GNR modified by NH3. We cannot help adopting the minimum size of a supercell because of the limitation of the performance of our computers. This size is considerably smaller than
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