Osonkie A, Lee V, Chukwunenye P, Cundari T, Kelber J
Department of Chemistry, University of North Texas, Denton, Texas 76203, USA.
J Chem Phys. 2020 Oct 14;153(14):144709. doi: 10.1063/5.0027996.
Plasma modification of transition metal nitride/oxynitride (MON) surfaces for enhanced surface properties is highly desirable, given the scalability of such methods and limitations of thermal treatments. In situ x-ray excited photoelectron spectroscopy demonstrates that the O plasma oxidation of VON films generates non-lattice N1s surface features with binding energies near 396.5 eV, which are associated with the nitrogen reduction reaction activity but not observed upon thermal oxidation. The NH plasma generates N1s surface features near 400.5 eV binding energy. The O+NH plasma generates both types of N1s features. Annealing in UHV to <1000 K reverses plasma-induced changes to N1s spectra. Density functional theory (DFT) calculations integrated with the experiments indicate that the plasma-induced N1s features at ∼396.5 eV and 400.5 eV are V≡N: and V-NH sites, respectively, with significantly lower thermal stabilities than lattice N sites. These results provide practical insight regarding the plasma modification of MON surfaces for important applications.
鉴于此类方法的可扩展性以及热处理的局限性，通过等离子体对过渡金属氮化物/氮氧化物（MON）表面进行改性以增强表面性能是非常可取的。原位X射线激发光电子能谱表明，VON薄膜的O等离子体氧化会产生结合能接近396.5 eV的非晶格N1s表面特征，这些特征与氮还原反应活性相关，但在热氧化时未观察到。NH等离子体会产生结合能接近400.5 eV的N1s表面特征。O + NH等离子体会产生两种类型的N1s特征。在超高真空（UHV）中退火至<1000 K会逆转等离子体诱导的N1s光谱变化。与实验相结合的密度泛函理论（DFT）计算表明，等离子体诱导的约396.5 eV和400.5 eV处的N1s特征分别为V≡N:和V-NH位点，其热稳定性明显低于晶格N位点。这些结果为MON表面等离子体改性在重要应用中的实际应用提供了见解。
