Graphyne nanotubes: New Families of Carbon Nanotubes
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Graphyne nanotubes: New Families of Carbon Nanotubes Vitor R. Coluci1,2, Scheila F. Braga1, Sergio B. Legoas1, Douglas S. Galvão1 and Ray H. Baughman2 1 Instituto de Física, Universidade Estadual de Campinas, 13083-970,Campinas, SP,Brazil 2 NanoTech Institute and Department of Chemistry, University of Texas at Dallas, 830688, Richardson, Texas ABSTRACT Fundamentally new families of carbon single walled nanotubes are proposed. These nanotubes, called graphynes, result from the elongation of covalent interconnections of graphitebased nanotubes by the introduction of yne groups. Similarly to ordinary nanotubes, armchair, zig-zag, and chiral graphyne nanotubes are possible. We present here results for the electronic properties of graphyne based tubes obtained from tight-binding and ab initio density functional methods. INTRODUCTION The early report of carbon nanotubes (CNTs) by Iijima [1] generated an enormous amount of research activity. New and exciting phenomena have been observed [2], from field emission to thermal conductivity higher than diamond [3-6]. Depending upon structure, the nanotubes are either metallic or insulating, which is a feature intensively investigated and exploited in prototype devices [2]. Alternative nanotube structures containing heteroatoms (N, B, etc.), as well as various carbon free nanofibers, have been recently synthesized [2]. While previous works have focused on graphitic nanotubes, we believe that other types of pure carbon nanotubes are feasible using different accessible hybridization states of carbon. One possibility that has been overlooked in the literature is to use graphyne sheets as structural motif for carbon nanotubes. The γ-graphyne [Fig. 1(c)] is the lowest energy member of a family of carbon phases consisting of planar molecular sheets containing only sp and sp2 carbon atoms. It is an allotropic form of carbon proposed by Baughman, Eckhardt, and Kertesz [7] in 1987, and has recently become the focus of new investigations [8, 9]. The presence of acetylene groups in these structures introduces a rich variety of optical and electronic properties quite different that from ordinary carbon nanotubes [10]. CNTs can be considered as formed by rolling up graphite sheets [2,11]. In the same way we can imagine graphyne nanotubes (GNTs) as formed by rolling up graphyne sheets to form seamless cylinders (Figs. 1 and 2). Preserving the (n,m) nomenclature, we defined the chiral vector Ch as Ch= na1 + ma2 = (n,m). Zig-zag and armchair tubes were then generated from the vectors (n,0) and (n,m), respectively. As there are many members in the graphyne family [7] new families of pure carbon nanotubes can be generated with diverse electronic and structural characteristics. Because of space constraints, we describe here in details only the results for two families of graphynes nanotubes, the α-graphynes (α-GNTs) and γ-graphynes (γ-GNTs) [Fig. 1 and Fig.2]. This choice was based on the fact that α-graphyne is the graphyne most analogous to graphene and the one with the
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