Molecular Dynamics Study of Electron Irradiation Damages in Carbon Nanomaterials
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1057-II10-28
Molecular Dynamics Study of Electron Irradiation Damages in Carbon Nanomaterials Masaaki Yasuda, Takashi Majima, Yoshihisa Kimoto, Kazuhiro Tada, Hiroaki Kawata, and Yoshihiko Hirai Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan ABSTRACT Molecular dynamics (MD) studies are carried out to investigate the electron irradiation damages in carbon nanomaterials. The interaction between an incident electron and a carbon atom is modeled based on the Monte Carlo method using the elastic scattering cross section. The electron irradiation damages in graphene, graphite, single-walled carbon nanotube (SWNT) and carbon nanopeapod are demonstrated. The cross-links in the nanostructures caused by the knockon effect are observed as typical structural damages. The dependence of the damages on the primary electron energy is shown for the SWNT. INTRODUCTION The study of the electron irradiation effects on nanomaterials takes on a growing importance in the resent progress of nanoscience. One of the motivations for this subject is the selection of the proper condition for a high resolution transmission electron microscope (TEM) observation. The high energy electron irradiation in TEM observation frequently causes serious damages in the nanomaterials. Furthermore, the properties obtained under TEM observation are more or less affected by electron irradiation. Another incentive for this subject is a modification of the nanomaterials by electron irradiation. Various attractive effects are demonstrated especially in carbon nanomaterials [1,2]. In our previous paper, we proposed a MD simulation including the electron-carbon atom interaction using the Monte Carlo method and reported the electron irradiation effects in SWNTs [3]. In the study, we demonstrated the deformation process of SWNT under the electron irradiation in nanosecond time scale. We also studied the dependences of the irradiation effects on the incident electron energy, tube diameter and tube temperature. In the present study, we demonstrate the electron irradiation effects in various carbon nanomaterials with the simulation. SIMULATION The scattering angle of the incident electron, ω, is determined by the following screened Rutherford cross section [4]:
dσ e 4 Z (Z + 1) = 2 4 , dΩ me v (1 − cos ω + 2 β )2
(1)
where me is the electron mass, v the electron velocity, e the electron charge, Z the atomic number and β the screening parameter. Once the scattering angle of incident electron is determined, the transferred energy from the electron to the carbon atom, Et, and the scattering angle of the carbon
atom from the incident axis,θ , are obtained based on the binary collision model as follows :
⎧ ⎛ m cos ω + mc2 − me2 sin 2 ω ⎪ Et = ⎨1 − ⎜ e ⎜ me + mc ⎪⎩ ⎝ cos θ =
(me + mc )2 4 m e mc
⋅
⎞ ⎟ ⎟ ⎠
2
⎫ ⎪ ⎬E0 , ⎪ ⎭
(2)
Et , E0
(3)
where mc is the mass of a carbon atom and E0 the incident electron energy. The scattering angle of the carbon atom around the axis, φ, is distributed uniformly. The collision atom
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