Atomic-scale simulations of radiation effects in GaN and carbon nanotubes
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Atomic-scale simulations of radiation effects in GaN and carbon nanotubes
K. Nordlund , J. Nord , A. V. Krasheninnikov and K. Albe Accelerator Laboratory, P.O. Box 43, FIN-00014 University of Helsinki, Finland Institut f¨ur Materialwissenschaft, TU Darmstadt, D-64287 Darmstadt, Germany
ABSTRACT Gallium nitride and carbon nanotubes have received wide interest in the materials research community since the mid-1990’s. The former material is already in use in optoelectronics applications, while the latter is considered to be extremely promising in a wide range of materials. Common to both materials is that ion irradiation may be useful for modifying their properties. In this paper we overview our recent molecular dynamics simulations results on ion irradiation of these materials. We employ such potentials to study the basic physics of how ion irradiation affects these materials. In particular we discuss the reasons for the high radiation hardness of GaN, and the surprising nature of vacancies and interstitials in carbon nanotubes. INTRODUCTION Molecular dynamics (MD) computer simulations have become well established as the main tool for studying the primary state of radiation damage in materials. Interatomic potentials exist for almost all elements of broad application interest, and MD methods have indeed been used to examine issues such as point and extended defect production, phase changes and sputtering in a wide range of elemental materials. Studies of compounds and multicomponent systems, by contrast, have been hampered by a lack of interatomic potentials for compounds. If a mixed system containing elements A and B only has a few mixed A-B bonds (say e.g. in a multilayer system), and no mixing of the materials occurs, one can use any elemental model for A and B, and a simple pair potential may be good enough to handle the A-B interactions. If one is, however, interested in a true alloy of AB, where mixing or segregation of the elements may occur, the requirements placed on the potential are much more severe. One needs elemental models for A and B and a mixed interaction term A-B which describes the main mixed phases correctly in terms of heat of mixing and structure. We have recently developed mixed interactions for the systems GaAs, GaN and PtC which can describe well all the pure elements involved, as well as the mixed phase. In this paper we first briefly describe our potential construction approach, then proceed to present application of the models to study the high radiation hardness of GaN and irradiation of carbon nanotubes lying on a heavy metal (Pt) substrate. SIMULATION METHOD The bond-order potential formalism advocated by Abell [1] and made widely popular by the practical implementation for Si by Tersoff [2] has proven to be a good starting point
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for development of analytical potentials. The work by Abell gives a good physical motivation for why a single functional form can be applied to a wide range of materials, as well as a wide range of coordinations of the same material. The
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