Interfacial Structure of Ti2AlN Thin Films on MgO(111)

Single-crystalline Ti2AlN thin films have been grown on MgO(111) substrates at 750 C using DC magnetron sputtering from a Ti2Al alloy target in a mixed N-2/Ar plasma. X-ray diffraction and transmission electron microscopy confirm epitaxial layered growth of Ti2AlN (0001) on MgO(111). On the basis of the experimental results, ab initio calculations were carried out to study the geometry and electronic structure between Ti2AlN and oxygen/magnesium -terminated MgO polar surfaces. A total of eight interface structures were calculated, and results showed that the adhesion between Ti2AlN (0001) and O-terminated MgO(111) is stronger than that with Mg-terminated MgO(111) surfaces in general. In particular, the largest adhesion energy was found for the interfacial structure with N-Ti-Al-Ti/O-Mg configuration. The stronger adhesion is due to reactive nature of Ti2AlN surface with N-Ti-Al-Ti stacking sequence. In addition, electronic structure calculation results showed that there is charge transferring between Ti2AlN and MgO with directions from Ti2AlN to MgO for O termination and from MgO to Ti2AlN for Mg termination. Moreover, the adhesion energies and charge-transferring amount are independent of the layer thickness of Ti2AlN, indicating that the interaction between Ti2AlN and MgO is rather localized.