On the Formation of Carbon Nanotube Serpentines: Insights from Multi-Million Atom Molecular Dynamics Simulation
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On the Formation of Carbon Nanotube Serpentines: Insights from Multi-Million Atom Molecular Dynamics Simulation Leonardo D. Machado1, Sergio B. Legoas2, Jaqueline S. Soares3, Nitzan Shadmi4 , Ado Jorio3, Ernesto Joselevich4, and Douglas S. Galvao1 1 Applied Physics Department, State University of Campinas, Campinas-SP, 13083-459, Brazil. 2 Physics Department, Federal University of Roraima, Boa Vista-RR, 69304-000, Brazil. 3 Physics Department, Federal University of Minas Gerais, Belo Horizonte-MG, 30123-970, Brazil. 4 Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 76100, Israel. ABSTRACT In this work we present preliminary results from molecular dynamics simulations for carbon nanotubes serpentine dynamics formation. These S-like nanostructures consist of a series of parallel and straight nanotube segments connected by alternating U-turn shaped curves. Nanotube serpentines were experimentally synthesized and reported in recent years, but up to now no atomistic simulations have been carried out to address the dynamics of formation of these structures. We have carried out fully atomistic molecular dynamics simulations in the framework of classical mechanics with a standard molecular force field. Multi-million atoms structures formed by stepped substrates with a carbon nanotube (about 1 micron in length) placed on top of them have been considered in our simulations. A force is applied to the upper part of the tube during a short period of time and then turned off and the system set free to evolve in time. Our results showed that these conditions are sufficient to form robust serpentines and validate the general features of the ‘falling spaghetti mechanism’ previously proposed to explain their formation. INTRODUCTION Carbon nanotube serpentines (CNSs) are S-like nanostructures composed of regularly spaced and parallel straight segments, connected by alternating U-turn shaped curves. These remarkable structures have been experimentally obtained growing long carbon nanotubes on sapphire and quartz patterned substrates under the presence of a flow gas flux [1,2,3,4]. CNSs were firstly synthesized in 2008 by the Joselevich’s group [1]. Recently, other groups have reported similar results [2-5]. CNS formation has been qualitatively explained based on the “falling spaghetti mechanism” [1]. The serpentines would be formed in a two-step process, where the isolated nanotubes are first grown standing up from the stepped substrates, and at a second stage, the tube would fall down preferentially along the steps, creating the oscillatory patterns, like spaghetti falling on a tilted bamboo mat [1]. The force that would be primarily responsible for the tube fall is the strong nanotube-surface interactions (mainly van der Waals forces). In this case, the growing nanotube is buoyant over the substrate and is submitted to a tension by the action of a gas flow perpendicular to the steps. After starting to fall the nanotube initiates an oscillatory motion with the tube being adsorbed by the substrate in a s
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