Interface Structure and Stability in Ti/c Superlattices

We have performed a coordinated experimental and theoretical investigation of the structure and stability of Ti/C multilayers. The samples were prepared by conventional techniques and the lattice structure was characterized by X-ray diffraction. Electron Energy Loss and Auger spectroscopies (EELS,AS), in conjunction with Rutherford Backscattering (RBS) were employed to characterize the chemical composition of the samples. It was observed that the Ti/C interface is isolated by a thin titanium oxide layer. The center of the Ti layer gives a typical EELS spectrum of Ti metal. The carbon shows a graphitic character. We have used total energy calculations to study the crystallographic structure and electronic behavior at the interface in Ti-C superlattices. This involved examining a series of structures in the Ti-C system proceeding from the ground state NaCl structure to superlattices. In particular we performed total energy calculations for an arrangement of atoms designed to allow direct investigation of the competition between Ti-C bonds and C-C bonds. We conclude that the equilibrium structure is dominated by C-C bonding and so we find that the interface has a graphite like atomic arrangement rather than a carbide like arrangement. We than further explored the interactions in this graphitic arrangement and found that the interface does not have a significant Ti-C bonding and that the interface most likely consists of simply a layer of graphite adjoining a titanium surface. This carries important implications for the diffusion and bonding at the interface.