Graciani J, Fdez Sanz J, Asaki T, Nakamura K, Rodriguez J A
Departamento de Química Física, Universidad de Sevilla, E-41012 Sevilla, Spain.
J Chem Phys. 2007 Jun 28;126(24):244713. doi: 10.1063/1.2743418.
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 O2 on TiN(001) was investigated at temperatures between 250 and 450 K. At the lowest temperature, there was chemisorption of oxygen (O(2,gas)-->2O(ads)) without significant surface oxidation. In contrast, at 450 K the amount of O2 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 N2 and NO was detected. The DFT calculations show that the adsorption/dissociation of O2 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 (DeltaE=2.84 eV). However, the overall oxidation of the surface layer is thermodynamically favored due to the energy released by the dissociative adsorption of O2 and the formation of N2 or NO. Both experimental and theoretical results lead to conclude that a TiN+mO2 -->TiOx + NO reaction is an important exit channel for nitrogen in the oxidation process.
这项工作结合基于同步辐射的光电子能谱和密度泛函理论（DFT），对TiN(001)的氧化进行了详细的实验和理论研究。在实验方面，研究了在250至450 K温度范围内O₂在TiN(001)上的吸附情况。在最低温度下，存在氧的化学吸附（O(2,气体)→2O(吸附)），且无明显的表面氧化。相反，在450 K时，吸附的O₂量持续增加，没有证据表明存在氧饱和覆盖，Ti 2p芯能级谱中的清晰信号表明存在TiOx物种，并且检测到了N₂和NO的脱附。DFT计算表明，O₂在TiN(001)衬底上的吸附/解离是高度放热的，且主要由Ti中心进行。高氧覆盖率（大于0.5 ML）可能会诱导表面的一些结构重构。表面N原子被O吸附原子取代是一个高度吸热的过程（ΔE = 2.84 eV）。然而，由于O₂的解离吸附以及N₂或NO的形成所释放的能量，表面层的整体氧化在热力学上是有利的。实验和理论结果均得出结论，即TiN + mO₂→TiOx + NO反应是氧化过程中氮的一个重要逸出通道。
