Osonkie Adaeze, Lee Veronica, Oyelade Adeola, Mrozek-McCourt Maximillian, Chukwunenye Precious, Golden Teresa D, Cundari Thomas R, Kelber Jeffry A
Department of Chemistry, University of North Texas, Denton, TX 76203, USA.
Phys Chem Chem Phys. 2020 Nov 14;22(42):24640-24648. doi: 10.1039/d0cp04168h. Epub 2020 Oct 25.
The chemical structures of Co oxynitrides - in particular, interactions among N and O atoms bonded to the same cobalt - are of great importance for an array of catalytic and materials applications. X-ray diffraction (XRD), core and valence band X-ray photoelectron spectroscopy (XPS) and plane wave density functional theory (DFT) calculations are used to probe chemical and electronic interactions of nitrogen-rich CoON (x > 0.7) films deposited on Si(100) using NH or N plasma-based sputter deposition or surface nitridation. Total energy calculations indicate that the zinc blende (ZB) structure is energetically favored over the rocksalt (RS) structure for x > ∼0.2, with an energy minimum observed in the ZB structure for x∼ 0.8-0.9. This is in close agreement with XPS-derived film compositions when corrected for surface oxide/hydroxide layers. XRD data indicate that films deposited on Si(100) at room temperature display either a preferred (220) orientation or no diffraction pattern, and are consistent with either rocksalt (RS) or zinc blende (ZB) structure. Comparison between experimental and calculated X-ray excited valence band densities of states - also similar for all films synthesized herein - demonstrates a close agreement with a ZB, but not an RS structure. Core level XPS spectra exhibit systematic differences between films deposited in NH vs N plasma environments. Films deposited by N plasma magnetron sputtering exhibit greater O content as evidenced by systematic shifts in N 1s binding energies. Excellent agreement with experiment for core level binding energies is obtained for DFT calculations based on the ZB structure, but not for the RS structure. The agreement between theory and experiment demonstrates that these N-rich Co oxynitride films exhibit the ZB structure, and forms the basis of a predictive model for understanding how N and O interactions impact the electronic, magnetic and catalytic properties of these materials.
钴氮氧化物的化学结构——特别是与同一钴原子键合的氮原子和氧原子之间的相互作用——对于一系列催化和材料应用非常重要。利用X射线衍射（XRD）、芯能级和价带X射线光电子能谱（XPS）以及平面波密度泛函理论（DFT）计算，来探究使用基于NH或N等离子体的溅射沉积或表面氮化法在Si(100)上沉积的富氮CoON（x > 0.7）薄膜的化学和电子相互作用。总能量计算表明，当x > ∼0.2时，闪锌矿（ZB）结构在能量上比岩盐（RS）结构更有利，在x∼ 0.8 - 0.9时，ZB结构中观察到能量最小值。当对表面氧化物/氢氧化物层进行校正时，这与XPS得出的薄膜成分密切一致。XRD数据表明，在室温下沉积在Si(100)上的薄膜显示出择优的（220）取向或没有衍射图案，并且与岩盐（RS）或闪锌矿（ZB）结构一致。本文合成的所有薄膜的实验和计算得到的X射线激发价带态密度之间的比较——也都相似——表明与ZB结构密切一致，但与RS结构不一致。芯能级XPS光谱显示在NH等离子体环境和N等离子体环境中沉积的薄膜之间存在系统差异。通过N等离子体磁控溅射沉积的薄膜表现出更高的氧含量，这由N 1s结合能的系统偏移证明。基于ZB结构的DFT计算在芯能级结合能方面与实验结果非常吻合，但对于RS结构则不然。理论与实验之间的一致性表明，这些富氮钴氮氧化物薄膜呈现ZB结构，并构成了一个预测模型的基础，用于理解氮和氧的相互作用如何影响这些材料的电子、磁性和催化性能。
