Thermal atomic layer etching (ALE) of nickel (Ni) may be performed with a step of thin-layer oxidation of its surface and another step of its removal by gas-phase hexafluoroacetylacetone (hfacH) as an etchant. In this study, adsorption of hfacH and possible formation of volatile nickel hexafluoroacetylacetonate Ni(hfac)₂ on a NiO surface were investigated based on the density functional theory (DFT) with more realistic surface material models than those used in the previous study [A. H. Basher et al., J. Vac. Sci. Technol. A 38, 022610 (2020)]. It has been confirmed that an hfacH molecule approaching a NiO surface deprotonates without a potential barrier and adsorbs on the surface exothermically. In addition, stable adsorption of two deprotonated hfacH molecules on a NiO (100) surface was found to occur not on a single Ni atom but over a few Ni atoms instead, which makes the formation of a Ni(hfac)₂ complex on the flat surface very unlikely even at elevated temperature. However, if the surface is rough and a Ni atom protrudes from the surrounding atoms, two hexafluoroacetylacetonate anions (hfac⁻) can bond to the Ni atom stably, which suggests a possibility of desorption of a Ni(hfac)₂ complex from the surface at elevated temperature. Given the experimentally observed fact that desorption of Ni(hfac)₂ complexes typically takes place on a NiO surface at a temperature of ∼300–400 °C, our DFT calculations indicate that the surface roughness of an oxidized Ni surface facilitates the formation and desorption of organometallic complexes Ni(hfac)₂, and therefore, the resulting Ni surface after ALE can be smoother than the initial surface.

中文翻译：

---

原子层蚀刻工艺中六氟乙酰丙酮化镍Ni（hfac）2在氧化镍表面上的形成和脱附

镍（Ni）的热原子层蚀刻（ALE）可以通过其表面的薄层氧化步骤和通过气相六氟乙酰丙酮（hfacH）作为蚀刻剂去除其的另一步骤来进行。在这项研究中，基于密度泛函理论（DFT），研究了hfacH的吸附以及在NiO表面上形成挥发性六氟乙酰丙酮化镍Ni（hfac）_2的可能性，其表面材料模型比以前的研究更为实际[AH Basher等。，J。Vac。科学 技术。A 38，022610（2020）]。已经证实，接近NiO表面的hfacH分子在没有势垒的情况下去质子化并且放热地吸附在表面上。此外，两个去质子化的hfacH分子在NiO（100）表面上的稳定吸附不是在单个Ni原子上发生，而是在几个Ni原子上发生，这使得在平面上形成了Ni（hfac）₂络合物。即使在高温下，表面也不太可能。然而，如果表面是粗糙的，并从周边原子的镍原子突出，六氟乙酰丙酮2个阴离子（HFAC ^- ）可以结合在Ni原子稳定，这表明镍（HFAC）的解吸的可能性₂在高温下从表面形成复合物。根据实验观察到的事实，Ni（hfac）₂络合物的解吸通常在温度约为300-400°C的NiO表面上进行，我们的DFT计算表明氧化的Ni表面的表面粗糙度有助于形成和解吸由于有机金属配合物Ni（hfac）_2的存在，因此，ALE后所得的Ni表面可以比初始表面光滑。