  A series of density functional theory (DFT) simulations was performed to
investigate the approach, contact, and subsequent separation of two atomically
flat surfaces consisting of different materials. Aluminum (Al) and titanium
nitride (TiN) slabs were chosen as a model system representing a metal-ceramic
interface and the interaction between soft and hard materials. The approach and
separation were simulated by moving one slab in discrete steps normal to the
surfaces allowing for electronic and atomic relaxations after each step.
Various configurations were analyzed by considering (001), (011), and (111)
surfaces as well as several lateral arrangements of these surfaces at the
interface. Several tests were conducted on the computational setup, for
example, by changing the system size or using different approximations for the
exchange correlation functional. The performed simulations revealed the
influences of these aspects on adhesion, equilibrium distance, and material
transfer. These interfacial properties depend sensitively on the chosen
configuration due to distinct bond situations. Material transfer, in
particular, was observed if the absolute value of the adhesion energy for a
given configuration is larger than the energy cost to remove surface layers.
This result was found to be independent of the employed exchange correlation
functional. Furthermore, it was shown that a simple comparison of the surface
energies of the slabs is not sufficient to predict the occurrence of material
transfer.
