Carbon-ceramic (AlN) interfaces from liquid quench ab initio molecular dynamics simulations

We report on the structure of carbon-ceramic interface models obtained by quenching a carbon liquid in between two identical crystalline surfaces of aluminium nitride using ab initio molecular dynamics simulations. Two kinds of neutral and non-polar surfaces [(11 (2) over bar0) and (10 (1) over bar0)] were studied. The models obtained in both cases show typical disordered graphitic carbon domains with well-defined anisotropic nanotextures, while a bulk carbon system quenched in the same conditions leads to a nearly isotropic amorphous solid. The graphene layers of the nanocomposite with (11 (2) over bar0) surfaces develop parallel to the latter, showing weak interface bonding. On the contrary, they develop normally to the (10 (1) over bar0) surfaces, with many covalent bonds connecting each graphene layer to both surfaces. Finally, by looking at the mobility of carbon atoms during the quench simulations, we show that carbon actually gets bonded to (10 (1) over bar0) surfaces much before the temperature reaches its melting point. This indicates that the solidification of the carbon phase is strongly catalysed by the presence of surfaces. It does not happen when (11 (2) over bar0) surfaces are used. In this case, no clear distinction can be observed between the self-diffusivity coefficients of carbon in the nanocomposite and those in the bulk carbon system, whatever the temperature.