Interaction of oxygen with TiN(001):N⇆O exchange and oxidation process

This work presents a detailed experimental and theoretical study of the oxidation of TiN(001) using a combination of synchrotron-based photoemission and density functional theory (DFT). Experimentally, the adsorption of O-2 on TiN(001) was investigated at temperatures between 250 and 450 K. At the lowest temperature, there was chemisorption of oxygen (O-2,O-gas -> 2O(ads)) without significant surface oxidation. In contrast, at 450 K the amount of O-2 adsorbed increased continuously, there was no evidence for an oxygen saturation coverage, a clear signal in the Ti 2p core level spectra denoted the presence of TiOx species, and desorption of both N-2 and NO was detected. The DFT calculations show that the adsorption/dissociation of O-2 is highly exothermic on a TiN(001) substrate and is carried out mainly by the Ti centers. A high oxygen coverage (larger than 0.5 ML) may induce some structural reconstructions of the surface. The exchange of a surface N atom by an O adatom is a highly endothermic process (Delta E=2.84 eV). However, the overall oxidation of the surface layer is thermodynamically favored due to the energy released by the dissociative adsorption of O-2 and the formation of N-2 or NO. Both experimental and theoretical results lead to conclude that a TiN+mO(2)-> TiOx+NO reaction is an important exit channel for nitrogen in the oxidation process. (c) 2007 American Institute of Physics.