From Alloy to Oxide: Capturing the Early Stages of Oxidation on Ni-Cr(100) Alloys.
From Alloy to Oxide: Capturing the Early Stages of Oxidation on Ni-Cr(100) Alloys.
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DOI：
10.1021/acsami.8b15210
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发表时间：
2018-11
影响因子：
9.5
通讯作者：
William H. Blades;P. Reinke
中科院分区：
文献类型：
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作者：
William H. Blades;P. Reinke
用扫描隧道显微镜(STM)和能谱(STS)研究了氧与Ni-Cr(100)合金表面的相互作用，观察了合金-氧化物界面的初始氧化过程和形成过程。观察了原位生长在MgO(100)衬底上的Ni-8wt%Cr(100)和Ni-12wt%Cr(100)薄膜的氧化过程。这些表面在500℃下暴露在1到150的L O2中，并在500和600℃下进行额外的热处理步骤。每个氧化和退火步骤都用扫描隧道显微镜和扫描隧道显微镜进行研究，微分电导图提供了关于掺杂和带隙分布的空间分辨信息。NiO最初的形核和生长是沿着Ni-Cr合金的台阶边缘开始的，并伴随着阶梯上小颗粒氧化物的形成。镍铬合金表面没有Ni(100)氧化的孕育期，说明铬合金化引起了表面化学的显著变化。台阶边缘刻面是通过沿台阶边缘的氧化物装饰来启动的，并在STM图像中表示为莫尔图案。表面氧化物可以用NiONi(6×7)和NiO-Ni(7×8)符合晶格表征，它们具有立方对立方的外延关系。在退火过程中，NiO的小斑块容易被还原；然而，额外的氧化物覆盖稳定了NiO。NiO区域散布着以一种新的交叉型重建为主的区域，该区域暂时被解释为富铬、相分离的区域。统计分析了表面氧化物的几何特征，包括台阶边缘高度和NiO楔形角，说明了NiO在前Cabrera-Mott区的逐层生长模式，以及氧化过程中合金-氧化物界面的重构。这一实验方法提供了对镍铬薄膜中氧化物生长过程的更多洞察，并强调了合金化对前卡布雷拉-莫特制度下氧化过程的巨大影响。
The interaction of oxygen with Ni-Cr(100) alloy surfaces is studied using scanning tunneling microscopy (STM) and spectroscopy (STS) to observe the initial steps of oxidation and formation of the alloy-oxide interface. The progression of oxidation was observed for Ni(100) and Ni-Cr(100) thin films including Ni-8 wt % Cr(100) and Ni-12 wt % Cr(100), which were grown on MgO(100) in situ. These surfaces were exposed to between 1 and 150 L O2 at 500 °C, and additional annealing steps were performed at 500 and 600 °C. Each oxidation and annealing step was studied with STM and STS, and differential conductance maps delivered spatially resolved information on doping and band gap distributions. Initial NiO nucleation and growth begins along the step edges of the Ni-Cr alloy accompanied by the formation of small oxide particles on the terraces. The incubation period known in oxidation of Ni(100) is absent on Ni-Cr alloy surfaces illustrating the significant changes in surface chemistry triggered by Cr-alloying. Step edge faceting is initiated by oxide decoration along the step edges and is expressed as moiré patterns in the STM images. The surface oxide can be characterized by NiONi(6 × 7) and NiO-Ni(7 × 8) coincidence lattices, which have a cube-on-cube epitaxial relationship. Small patches of NiO are susceptible to reduction during annealing; however, additional oxide coverage stabilizes the NiO. NiO regions are interspersed with areas covered predominantly with a novel cross-type reconstruction, which is interpreted tentatively as a Cr-rich, phase-separated region. Statistical analysis of the geometric features of the surface oxide including step edge heights, and NiO wedge angles illustrates the layer-by-layer growth mode of NiO in this pre-Cabrera-Mott regime, and the restructuring of the alloy-oxide interface during the oxidation process. This experimental approach has offered greater insight into the progression of oxide growth in Ni-Cr thin films and underscores the dramatic impact of alloying on oxidation process in the pre-Cabrera-Mott regime.