On the Unzipping Mechanisms of Carbon Nanotubes: Insights from Reactive Molecular Dynamics Simulations
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On the Unzipping Mechanisms of Carbon Nanotubes: Insights from Reactive Molecular Dynamics Simulations Ricardo P. dos Santos1, Pedro A. Autreto2, Eric Perim2, Gustavo Brunetto2, and Douglas S. Galvao2 1 Physics Department, IGCE, Universidade Estadual Paulista, UNESP, 13506-900, Rio Claro, SP, Brazil. 2 Applied Physics, State University of Campinas, 13083-970, Campinas, São Paulo, Brazil. ABSTRACT Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for the controlled and large-scale production of graphene nanoribbons (GNR). These structures are considered of great importance for the development of nanoelectronics because of its dimensions and intrinsic nonzero band gap value. Despite many years of investigations some details on the dynamics of the CNT fracture/unzipping processes remain unclear. In this work we have investigated some of these process through molecular dynamics simulations using reactive force fields (ReaxFF), as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. We considered multi-walled CNTs of different dimensions and chiralities and under induced mechanical stretching. Our preliminary results show that the unzipping mechanisms are highly dependent on CNT chirality. Well-defined and distinct fracture patterns were observed for the different chiralities. Armchair CNTs favor the creation of GNRs with well-defined armchair edges, while zigzag and chiral ones produce GNRs with less defined and defective edges. INTRODUCTION The unique and unusual electronic properties of graphene make it a very promising material for the creation of new nanodevices [1-3]. However, its zero band gap value hinders many possible technological applications making band gap engineering an important issue in order to overcome these limitations [4, 5]. Many different approaches have been tried to create, in a controllable way, a nonzero gap value in graphene-like structures. These approaches included hydrogenation [6], fluorination [7] and/or other chemical and physical functionalizations. These methods have achieved only limited successes. Another possibility it is to use the so-called graphene nanoribbons (GNRs). GNRs are basically long thin graphene strips [8]. Due to their small dimensions and active electronic edge states, GNRs can exhibit finite (nonzero) band gap values, which can be easily tuned depending on the their geometric features [8]. However, the controlled GNR synthesis remains a challenge up to the present. A new and very promising approach is to obtain GNRs from the unzipping of carbon nanotubes (CNTs), in which CNTs are fractured (unzipped) along their longitudinal axis in a way that the obtained fractured structures are the GNRs. This can be experimentally realized by chemical [9] or physical methods [10].
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Figure 1. Scheme of the atomistic model used in the molecular dynamics simulations. Defective external tube atoms (cyan) are free to move. Inner CNT atoms (purple) are held fixed. Red bands represent ''clamped'' atoms, which a
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