Ab initiostudy of Ti0.5Al0.5N(001)—residual and environmental gas interactions

We have explored surface processes on Ti 0.5 Al 0.5 N(001) interacting with residual and environmental gases, namely O 2 , H 2 O and CO 2 , using ab initio molecular dynamics. Dissociative adsorption of O 2 occurs on Ti sites, which are unusual sites, as Al 2 O 3 is more stable than TiO 2 . This may be understood based on the electronic structure. We suggest that an increased Ti–O bond strength relative to Al–O surface bond strength is the electronic origin for the early stages of TiO 2 formation on Ti 0.5 Al 0.5 N(001). Another unexpected atomic mechanism, identified as O covers the surface: Ti escapes from the Ti 0.5 Al 0.5 N(001)/O interface layer, generating vacancies, and hence enabling mobility at the interface. In the case of H 2 O and CO 2 , the dominating physical mechanism is dissociative adsorption, where O–H and N–H as well as C–O and Ti–O dipoles are formed, respectively. These fundamental surface processes are relevant for initial stages of oxidation, surface diffusion and nucleation of reaction layers upon exposure to residual and environmental gases.