Interaction volume of electron beam in carbon nanomaterials: A molecular dynamics study
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Interaction volume of electron beam in carbon nanomaterials: A molecular dynamics study Masaaki Yasuda, Shinya Wakuda, Yoshiki Asayama, Hiroaki Kawata and Yoshihiko Hirai Osaka Prefecture University, Sakai, Osaka 599-8531, Japan ABSTRACT A molecular dynamics (MD) simulation was performed to study the interaction volume of electron beam in carbon nanomaterials. The interaction between incident electron and carbon atom in the target materials during electron irradiation is introduced by the relativistic binary collision theory. The motion of each atom in the material under electron irradiation is calculated with the MD simulation. The primary energy dependence of the interaction volume in the carbon nanotube and the multi-layered graphene are studied. The secondary damages caused by the knock-on atoms are also discussed. INTRODUCTION Irradiating carbon nanomaterials with energetic electrons is expected to become a technique to tailor the structure with desirable properties [1-3]. Cutting [4], bending [5] and welding [6] of carbon nanotubes by electron beam irradiation has been demonstrated. Graphene nanostructures sculpted by electron beam irradiation have been reported [7]. Pill shaped capsules were produced by coalescing C60 molecules under electron irradiation [8]. However, such structural modifications of carbon nanomaterials with electron beams are not well established at present. Understanding the atomic level behavior of the materials under electron irradiation becomes important. Molecular dynamics (MD) simulation is suitable to understand the atomic level behavior of the materials. Several MD simulations have been used to study irradiation-induced defects in carbon nanomaterials [9, 10] and have demonstrated the structural modification of nanomaterials with electron beam [11]. In those studies, a continuous random atom extraction [9] or atom ejection with constant velocity [10, 11] has been introduced as the electron irradiation effects. Electron knock-on cross section [12] and the displacement energy [13] of carbon atoms in singlewalled carbon nanotubes (SWCNTs) have been also precisely calculated from the MD simulation. However, an electron bombardment process has not been explicitly included into a simulation of the deformation of carbon nanomaterials. In our previous studies, we presented MD simulations including electron irradiation effects based on a Monte Carlo method to study the deformation process of carbon nanostructures under electron irradiation. We investigated the structural changes of SWCNTs [14, 15] and graphene [16] caused by electron irradiation. We have reported the changes of the mechanical properties of electron-irradiated SWCNTs [17]. We also studied the correlation between electron irradiation defects and applied stress in SWCNTs [18]. In order to achieve precise modifications of the nanostructures, the control of the interaction volume of electron irradiation becomes important. Because the mean free path of the high energy electron in the carbon nanostructure is enough long, the multip
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