Electronic properties of CoO(100) surfaces: Defects and chemisorption.
Electronic properties of CoO(100) surfaces: Defects and chemisorption.
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DOI：
10.1103/physrevb.39.6156
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发表时间：
1989-03
期刊：
影响因子：
--
通讯作者：
Mackay;Henrich
中科院分区：
文献类型：
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作者：
Mackay;Henrich
紫外光电子能谱、俄歇电子能谱和低能电子衍射已被用来研究在超高真空中劈裂单晶获得的CoO(100)表面的电子结构。确定了 Ar+ 离子轰击可产生的两种不同类型的表面缺陷态。两种类型的缺陷都是由表面附近的氧空位引起的。第一类缺陷主要由表面氧空位组成；它是在表面发生任何程度的还原后形成的，并且即使在裂开的表面上也可能以很小的浓度存在。其电子结构根据 Co 离子在缺陷位点的交换和配体场分裂 d 轨道的占据来解释。第二种类型的缺陷仅在表面大量还原后出现，可能由相互作用的氧空位或钴原子簇组成。还研究了室温下 O 2 、CO 和 H 2 O 与近乎完美的表面以及与含有一种或两种类型缺陷的表面的相互作用。近乎完美的表面对于所研究的所有三种分子都相对惰性，仅在低于至少10 4 朗缪尔暴露的残留缺陷位点处表现出不反应或最小的化学吸附。 O 2 最初在两种类型的缺陷部位处解离吸附；高 O 2 暴露会产生分子吸附物质。暴露于 CO 会进一步减少主要包含第一类缺陷的表面，但不会减少包含两种类型缺陷的更严重的表面。 H 2 O 在严重还原的表面上解离吸附，导致吸附 OH− 离子。 CoO (100) 的结果与之前获得的 NiO (100) 和 MnO (100) 的结果进行了比较和对比。
Ultraviolet photoemission spectroscopy, Auger-electron spectroscopy, and low-energy electron diffraction have been used to study the electronic structure of CoO (100) surfaces obtained by cleaving single crystals in ultrahigh vacuum. Two distinct types of surface defect states that can be produced by Ar+-ion bombardment are identified. Both types of defects result from oxygen vacancies near the surface. The first type of defect consists primarily of surface oxygen vacancies; it forms after any degree of reduction of the surface and probably exists in small concentration even on cleaved surfaces. Its electronic structure is interpreted in terms of the occupation of exchange-and ligand-field–split d orbitals of Co ions at defect sites. The second type of defect appears only after heavy reduction of the surface and presumably consists of interacting oxygen vacancies or clusters of Co atoms. The interaction of O 2, CO, and H 2 O with the nearly perfect surface and with surfaces containing one or both types of defects at room temperature has also been investigated. The nearly perfect surface is relatively inert to all three molecules studied, exhibiting either no reaction or minimal chemisorption only at residual defect sites below at least 10 4 langmuir exposure. O 2 initially adsorbs dissociatively at both types of defect site; high O 2 exposures result in a molecularly adsorbed species. Exposure to CO further reduces surfaces that contain predominantly only the first type of defect, but not the more heavily reduced surfaces that contain both types of defects. H 2 O adsorbs dissociatively on the heavily reduced surface, resulting in adsorbed OH− ions. The results for CoO (100) are compared and contrasted with those obtained previously for NiO (100) and MnO (100).