In many nano-materials or devices composed of multiplayer of thin films, it is accepted that their physical and chemical properties are governed by the interfacial structure and properties. Due to insufficient understandings on the atomic structure of the interface, however, the properties of the nano-materials sometimes exhibit large difference from the prediction based on the conventional theories and observations. There is thus considerable interest in the atomic structure of interface or the structure evolution during the initial stage of the thin film deposition.
In the present work, we investigated the formation of amorphous carbon by molecular dynamic simulation using Tersoff's empirical potential. For the deposition of amorphous carbon, we used the neutral carbon atoms of high kinetic energy, bombarded on the diamond (100) surface. This simulation is similar to the experimental condition to obtain tetrahedral amorphous carbon (ta-C) films using filtered catholic arc process. Because of high hardness and wear resistance with optical transparency, the film has been investigated for various applications such as protective coating for mechanical component, IR optics, or MEMS devices.
By comparing the calculated lattice parameter, surface energy, elastic modulus and thermal expansion coefficient of diamond with the respective experimental values, the validity of the potential was tested. With increasing kinetic energy of the carbon atoms, the deposited film exhibited increased density, residual stress and hardness. Maximum density, residual compressive stress and hardness could be obtained when the kinetic energy was about 50 eV. When the kinetic energy was larger than 100eV, however, the density and hardness decreased with the kinetic energy. This behavior is in good agreement with the experimental observations and the number of atoms in the metastable site at the interatomic distance of about 0.22nm. The physical properties will be discussed in terms of the atomic bond structure. ta-C/diamond interface shows that the intermixing became significant when the kinetic energy increased.
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