Titanium nitride (TiN) is widely used in industry as a protective coating and a conducting layer due to its hardness, resistance to corrosion and conductivity. TiN can spontaneously form a thin oxide layer when exposed to air, which could modify the properties of the coating. With limited understanding of the TiO2–TiN interfacial system at present, this contribution presents a density functional theory (DFT) study of the the structural and electronic properties of oxidized TiN using the TiN(100)-rutile TiO2(110) interface as a model system. The small lattice mismatch gives good stability to the TiO2–TiN interface after depositing the oxide onto TiN through the formation of interfacial Ti–O bonds. Using DFT+U we show the presence of Ti3+cations in the TiO2 region, which are preferentially located next to the interface region as well as the rotation of the rutile TiO2 octahedra in the interface structure. The DFT+U TiO2 electronic density of states (EDOS) shows localized Ti3+ defect states forming in the midgap between the top edge of the valence and the bottom of the conduction band. We increase the complexity of our models by the introduction of nonstoichiometric compositions. The vacancy formation energies for Ti in TiN (Evac (Ti) ≥ 4.03 eV) are high but for oxygen removal of multiple interfacial oxygen sites is stable as a result of forming multiple interfacial Ti-O and Ti-N bonds. We further show that a structure with exchanged O and N can lie 0.82 eV higher in energy than the perfect system, suggesting the stability of structures with interdiffused O and N anions at ambient conditions. The presence of N in TiO2 introduces N 2p states localized between the top edge of the O 2p valence states and the midgap Ti3+ 3d states, thus reducing the band gap in the TiO2 region for the exchanged O/N interface EDOS. The outcomes of these simulations give us a most comprehensive insight on the atomic level structure and the electronic properties of oxidized TiN surfaces.

Structure and defects in the TiN-TiO2 rutile interface

255th National Meeting (2018)

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