Effects of Ion Irradiation on Supported Carbon Nanotubes and Nanotube-Substrate Interfaces
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Effects of ion irradiation on supported carbon nanotubes and nanotube-substrate interfaces
A. V. Krasheninnikov, K. Nordlund, and J. Keinonen Accelerator Laboratory, P.O. Box 43, FIN-00014 University of Helsinki, Finland
ABSTRACT We employ molecular dynamics to study the effects of ion irradiation on carbon nanotubes lying on different substrates. We show that defect production depends on the type of the substrate and that the damage is higher for metallic heavy-atom substrates than for light-atom substrates, since in the former case sputtered metal atoms and backscattered recoils produce extra damage in the nanotube. We further study the behavior of defects and demonstrate that although ions may severely damage nanotubes in a local region, the nanotube carbon network can heal such a strong localized damage due to defect migration and dangling bond saturation. Finally, we predict the pinning of nanotubes to substrates by forming nanotube-substrate bonds which appear near irradiation-induced defects. INTRODUCTION Recent experiments [1–6] on the irradiation of carbon nanotubes (NTs) with energetic particles revealed many new interesting phenomena, e.g., the coalescence [1] and welding [2] of NTs under electron irradiation, ion irradiation-induced changes in electrical coupling between NTs [3], surface reconstructions [4, 5], and modifications of mechanical properties [6]. Experiments also provide evidence that ion irradiation of nanotubes may be employed for fabricating metal nanowires on insulating substrates using the carbon tubes as masks [7]. These examples illustrate the demand for microscopic understanding of defect formation mechanisms in supported NTs (i.e., nanotubes on different substrates). Note that apart from the fact that supported NTs can be used as mask for making nanowires, tubes may be utilized in various key experiments. This may include scanning tunneling microscopy probing of the irradiated NTs [8] to locate and characterize irradiation-induced defects, or electronic transport studies on quasi-one-dimensional systems with disorder [9–11]. The presence of a substrate may play a dominant role on the damage production in supported NTs since in that case the nanotubes can be damaged by backscattered impinging particles or by atoms sputtered from the substrate. In this work, we study the ion irradiation of single-walled NTs on different substrates. For qualitative understanding of the physical processes involved, we considered two limiting cases: a heavy-atom metallic substrate and a light-atom substrate with covalent bonds between atoms. The former was chosen to be a platinum (111) surface, the latter a Bernal graphite (0001) surface. Noble metals [12, 13] and graphite [13, 14] have repeatedly been used as substrates in experimental studies on carbon NTs.
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SIMULATION METHOD The method used in this study has been described in detail in other publications [8, 15] and so only a brief outline will be given here. We used classical molecular dynamics [16] to model defect production in NTs under
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