Formation of Atomic Carbon Chains from Graphene Nanoribbons

📝 Abstract

The formation of one-dimensional carbon chains from graphene nanoribbons is investigated using it ab initio molecular dynamics. We show under what conditions it is possible to obtain a linear atomic chain via pulling of the graphene nanoribbons. The presence of dimers composed of two-coordinated carbon atoms at the edge of the ribbons is necessary for the formation of the linear chains, otherwise there is simply the full rupture of the structure. The presence of Stone-Wales defects close to these dimers may lead to the formation of longer chains. The local atomic configuration of the suspended atoms indicates the formation of single and triple bonds, which is a characteristic of polyynes.

💡 Analysis

The formation of one-dimensional carbon chains from graphene nanoribbons is investigated using it ab initio molecular dynamics. We show under what conditions it is possible to obtain a linear atomic chain via pulling of the graphene nanoribbons. The presence of dimers composed of two-coordinated carbon atoms at the edge of the ribbons is necessary for the formation of the linear chains, otherwise there is simply the full rupture of the structure. The presence of Stone-Wales defects close to these dimers may lead to the formation of longer chains. The local atomic configuration of the suspended atoms indicates the formation of single and triple bonds, which is a characteristic of polyynes.

📄 Content

Formation of Atomic Carbon Chains from Graphene Nanoribbons Edwin Hobi Jr.1,∗Renato B. Pontes1, A. Fazzio1,2, and Antˆonio J. R. da Silva1,3† 1Instituto de F´ısica, Universidade de S˜ao Paulo, CP 66318, 05315-970, S˜ao Paulo, SP, Brazil 2Centro de Ciˆencias Naturais e Humanas, Universidade Federal do ABC, Santo Andr´e, S˜ao Paulo,SP, Brazil 3Laborat´orio Nacional de Luz S´ıncrotron, Campinas, SP, Brazil (Dated: July 7, 2021) The formation of one-dimensional carbon chains from graphene nanoribbons is investigated using ab initio molecular dynamics. We show under what conditions it is possible to obtain a linear atomic chain via pulling of the graphene nanoribbons. The presence of dimers composed of two-coordinated carbon atoms at the edge of the ribbons is necessary for the formation of the linear chains, otherwise there is simply the full rupture of the structure. The presence of Stone-Wales defects close to these dimers may lead to the formation of longer chains. The local atomic configuration of the suspended atoms indicates the formation of single and triple bonds, which is a characteristic of polyynes. PACS numbers: 81.07.Gf, 61.46.Km, 62.25.-g, 71.15.Pd Nanoelectronics continuously searches for low dimen- sional systems which can be used either as nanocontacts or nanoconductors. Metallic nanowires, for example, are widely studied because they can present quantum con- ductance and the capacity to produce atomic chains[1, 2]. Carbon based-systems, such as carbon nanotubes[3] and more recently graphene and its derivatives[4], are another class of materials which have attracted strong interest. They present interesting mechanical and elec- tronic properties with great potential for applications in nanodevices. Useful properties, such as stability, flexibil- ity, charge carriers linear dispersion and high mobility, spin injection with long relaxation times and correlation lengths could lead to applications in spintronics. The possibility to join in the same system the fea- tures of one-dimensional wires and the properties of carbon based materials is a very exciting one. The electronic and transport properties of one dimensional carbon systems have already been studied by some groups[5, 6, 7, 8, 9, 10, 11]. However, the lack of re- liable and effective ways to produce 1D carbon chains have limited the studies of these systems. Recently, two groups[12, 13] employed a technique similar to the one used for the fabrication of metallic quantum wires[14] to obtain experimentally stable and rigid carbon atomic chains, which brought new attention to this subject and opened up a new avenue in the investigation of one- dimensional carbon-based systems. Even though this recent experimental work obtained these chains via removal of carbons atoms using the electron beam, one can envisage a situation where these chains could be obtained by stretching graphene nanoribbons[15, 16]. In the present work we theoretically address this question. We perform room temperature ab initio molecular dynamics (AIMD)[17] to investigate the formation of linear atomic carbon chains from graphene nanoribbons. We elucidate the mechanism of formation of these chains and show under what conditions it is pos- sible to form these wires. FIG. 1: Five representative geometries along the molecular dynamics simulations for structures (a) N1; (b) N2; and (c) N3. In (b) and (c), it is possible to see the transition from a graphene ribbon to a single carbon chain. We study graphene nanoribbons with a neck, as shown in Fig. 1. The electronic structure and forces were obtained via ab initio total energy density functional theory[18] calculations[19]. We have investigated three types of necks (Fig.1). In one of them the neck has only three-coordinated carbon atoms (Fig.1(a)), and this will be labeled from now on N1. In the other two systems there are additional carbon dimers at the neck, which have two-coordinated carbon atoms. In one of them only one dimer is added to one of the sides (Fig.1(b)), and in the other two dimers are symmetrically added to the two sides of the neck (Fig.1(c)). These systems will be labeled N2 and N3, respectively. In Fig.1 we present five representative geometries along the molecular dynamics for each one of these systems (see also movies S1-S3[20]). As can be seen, N1 did not form any one-dimensional car- bon chain whereas N2 and N3 formed one and two carbon arXiv:0912.2502v1 [cond-mat.mtrl-sci] 13 Dec 2009 2 chains, respectively. Thus, the important conclusion is that it seems necessary to have dimers of two-coordinated carbon atoms in order to form one-dimensional chains. In more detail, the system N1 evolved in such a way that the external carbon bonds in the neck broke al- most simultaneously, followed by a very rapid rupture of the central remaining bond. For N2, the rupture started at the opposite side from the two-coordinated car- bons dimer, and as a zipper mechanism the other three- coordinated carbon bonds subsequent

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