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首页> 外文期刊>The Journal of Chemical Physics >The atomic structure of low-index surfaces of the intermetallic compound InPd
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The atomic structure of low-index surfaces of the intermetallic compound InPd

机译：金属间化合物InPd的低折射率表面的原子结构

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The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to similar to 580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above similar to 660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (>= 750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and "global" measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature. (C) 2015 AIP Publishing LLC.
机译：金属间化合物InPd（具有宽组成范围的晶体结构的CsCl型）被认为是甲醇蒸汽重整的候选催化剂。该相的单晶已经生长，用于研究超高真空条件下的三个低折射率表面的结构，方法是使用低能电子衍射（LEED），X射线光电子能谱（XPS）和扫描隧道显微镜（STM） ）。在表面准备过程中，优先溅射会导致所有三个表面的顶部几层中的In耗尽。近表面区域保持少量Pd富集，直到退火至580 K为止。在580和660 K之间发生过渡，其中In向表面偏析，而近表面区域在类似于660 K上方变为In富集。如STM所观察到的，过渡过程伴随着LEED模式的锐化和平坦阶梯状形态的形成。已经为与此过程相关的不同表面确定了几个上层建筑。退火到较高温度（> = 750 K）会导致通过热蚀刻形成小平面，如（110）表面所示，其In组成接近立方相存在域的In-rich极限。如动态LEED分析所示，发现富Pd的InPd（111）与Pd端基的大体截断模型一致，而在较高温度下退火后，In富InPd（111）则与In端基一致体截断，与相对表面能的密度泛函理论（DFT）计算一致。对于（100）表面观察到更复杂的表面结构。另外，多晶样品的单个晶粒的特征在于微点XPS和LEED以及低能电子显微镜。基于与我们的单晶发现，DFT计算和先前文献的比较，解释了单个晶粒和“整体”测量的结果。 （C）2015 AIP Publishing LLC。

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