Atomistic calculations of composite interfaces

The modified embedded atom method (MEAM), an empirical extension of the embedded atom method (EAM) that includes angular forces, has been used to examine the interface between a silicon substrate and a thin overlayer of nickel. A brief review of the MEAM is given and parameters are determined for the Si-Ni system. As verification of the reliability of the model, the geometry, energy and elastic constants of a number of ideal Si-Ni compounds are calculated and are found to agree reasonably well with experiment and first-principles calculations. Planar defect energies are also presented. Calculations of the relaxed energy and geometry of a coherent 10 AA overlayer of Ni on Si(001) yield two similar structures, both of which were typified by a slightly rippled Ni structure relative to perfect FCC Ni. The lower-energy interface also contained rows of slightly shifted Ni atoms. It is found that significant differences occur between the energetics of a rigid or relaxed separation of the overlayer. Separation of the overlayer with a monolayer of Si atoms attached to the Ni yields a significantly lower-energy structure than separation exactly at the interface. The relaxed brittle fracture energy of this interface is found to be 1.5 J m^-2, which is significantly lower than the unrelaxed fracture energy of 4.8 J m^-2.