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MM: Fachverband Metall- und Materialphysik

MM 26: Poster Session

MM 26.15: Poster

Dienstag, 23. März 2010, 14:45–16:30, Poster C

First-principles study of superhard SiN_x/TiN nanocomposites — •Pawel Rodziewicz and Bernd Meyer — Interdisziplinäres Zentrum für Molekulare Materialien ICMM and Computer-Chemie-Centrum CCC, Universität Erlangen–Nürnberg

Nanocomposite materials based on TiN nanocrystalites embedded in an amorphous silicon nitride matrix with thickness of only a few atomic layers and composition close to Si₃N₄ show a superhardness similar to that of diamond. To elucidate the chemical origin of the material hardness and the exceptional strength of the SiN_x/TiN interfaces we have used DFT calculations in combination with Car-Parrinello molecular dynamics (CPMD) simulations to create and to investigate model SiN_x/TiN interface structures. As the first step we studied the initial stages of SiN_x layer formation on TiN(001) by adding successively silicon and nitrogen atoms to the TiN surface to form up to two monolayer thick SiN_x films with different composition. For a selected set of configurations, chosen on the basis of thermodynamic stability, we then applied a stepwise procedure based on heating, quenching and final geometry optimization to search for stable and energetically favorable amorphous structures of SiN_x films and stacks of SiN_x/TiN multilayers. The relative stability of the different model interface structures is analyzed in terms of Ti, Si and N coordination numbers, and the mechanical strength of the interfaces is assessed by the calculation of stress–strain curves to determine the ideal decohesion strength.