ATOMISTIC CALCULATIONS OF COMPOSITE INTERFACES

The modified embedded atom method (MEAM), an empirical extension of th e embedded atom method (EAM) that includes angular forces, has been us ed to examine the interface between a silicon substrate and a thin ove rlayer of nickel. A brief review of the MEAM is given and parameters a re 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 reasona bly well with experiment and first-principles calculations. Planar def ect energies are also presented. Calculations of the relaxed energy an d geometry of a coherent 10 angstrom overlayer of Ni on Si(001) yield two similar structures, both of which were typified by a slightly ripp led Ni structure relative to perfect FCC Ni. The lower-energy interfac e also contained rows of slightly shifted Ni atoms. It is found that s ignificant differences occur between the energetics of a rigid or rela xed separation of the overlayer. Separation of the overlayer with a mo nolayer of Si atoms attached to the Ni yields a significantly lower-en ergy structure than separation exactly at the interface. The relaxed b rittle fracture energy of this interface is found to be 1.5 J m-2, whi ch is significantly lower than the unrelaxed fracture energy of 4.8 J m-2.