Electron energy loss spectroscopic investigation of Co metal, CoO, and Co3O4 before and after Ar+ bombardment
Electron energy loss spectroscopic investigation of Co metal, CoO, and Co3O4 before and after Ar+ bombardment
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DOI：
10.1016/j.apsusc.2004.02.062
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发表时间：
2004-08-31
影响因子：
6.7
通讯作者：
Salaita, GN
中科院分区：
文献类型：
--
作者：
Hagelin-Weaver, HAE;Hoflund, GB;Salaita, GN
用X射线光电子能谱(XPS)和电子能量损失谱(ELS)研究了离子轰击前后溅射清洗的多晶钴金属箔和CoO+Co3O4粉末。ELS数据是使用100至1150 eV的主束能量收集的，以便区分表面特征和整体特征，并便于确定峰位置。结果表明，这些标准物质的ELS光谱有很大的不同，因此，应该可以在未来的催化剂表征研究中进行物种鉴定。从Co金属获得的主要表面特征出现在3.7和7.0 eV处，而主要的体能损失出现在8.2、9.8、23.1、25.7和28.1 eV处。尽管已经收集了关于Co EL和Co金属的电子结构的数据，但明确的峰分配是困难的。能量损耗区的带间跃迁来源于相对局域的Co3d倾斜态，但导带中空态的有限信息使得对Co ELS谱中能量损失特征的具体赋值具有挑战性。XPS分析表明，这两个样品主要由Co3O4组成，与Co3O4封端的CoO表面一致。经过长时间的Ar+溅射后，根据Co2p结合能区的高分辨谱，两种氧化物都是类CoO的。与XPS数据相一致的是，从输入的CoO和Co3O4得到的ELS光谱非常相似。相比之下，延长Ar+溅射时间后，CoO和Co3O4的ELS光谱有很大的不同。溅射对CoO的ELS谱没有明显的影响，表明用Ar+轰击不能去除Co3O4层。相反，溅射的Co3O4产生了看起来类似CoO的ELS光谱。从Co3O4获得的主要ELS特征位于2.5、6.7、22.1和25.0 eV，而Ar+溅射Co3O4(CoO)获得的主要ELS特征位于7.0、8.6、18.3、21.9和36.1 eV。Co3O4在6.7 eV和25.0 eV处的峰强度比明显高于CoO的7.0-21.9 eV峰强度比。尽管两个光谱中的几个能量损失重叠，使得识别困难，尽管强度差异很大，但每个化合物都有特定的峰，即Co3O4在2.5和28.5 eV处的能量损失，以及CoO在36.1 eV处的能量损失。因此，ELS可以用于区分这两种钴氧化物，并且可以从ELS数据中获得补充XPS数据的信息。(C)2004爱思唯尔B.V.保留所有权利。
X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (ELS) have been used to study a sputter-cleaned polycrystalline Co metal foil and CoO plus Co3O4 powders before and after ion bombardment. The ELS data have been collected using primary beam energies ranging from 100 to 1150 eV in order to distinguish between surface and bulk features and to facilitate determination of peak locations. It is shown that ELS spectra from these reference materials are considerably different and should, consequently, allow species identification in future catalyst characterization studies. The main surface features obtained from Co metal are observed at 3.7 and 7.0 eV, while the major bulk energy losses are located at 8.2, 9.8, 23.1, 25.7, and 28.1 eV. Despite the collected data on Co ELS and the electronic structure of Co metal, unambiguous peak assignments are difficult. Interband transitions in the energy loss region under investigation originate from the relatively localized Co 3d tilled states, but the limited information about the empty states in the conduction band make specific assignments of the energy loss features in the Co ELS spectra challenging. XPS analysis of as-entered CoO and Co3O4 reveals that both samples consist mainly of Co3O4, in agreement with a Co3O4-terminated CoO surface. After prolonged Ar+ sputtering both oxides are CoO-like according to high-resolution spectra of the Co 2p binding energy region. In agreement with the XPS data the ELS spectra obtained from as-entered CoO and Co3O4 are very similar. In contrast, ELS spectra obtained from CoO and Co3O4 after prolonged Ar+ sputtering are considerably different. The ELS spectra obtained from CoO are not altered significantly with sputtering suggesting that the Co3O4 layer cannot be removed using Ar+ bombardment. The sputtered Co3O4 instead gives rise to ELS spectra that appear CoO-like. The major ELS features in the spectra obtained from Co3O4 are located at 2.5, 6.7, 22.1, and 25.0 eV, while those obtained from Ar+-sputtered Co3O4 (CoO) are observed at 7.0, 8.6, 18.3, 21.9, and 36.1 eV The relative intensities of the features at 6-8 eV and 22-25 eV are considerably different in the two sets of spectra. The intensity ratio of the peaks at 6.7 and 25.0 eV in Co3O4 is significantly higher than the 7.0 to 21.9 eV peak intensity ratio of CoO. Although several of the energy losses in the two spectra overlap and make identification difficult despite the large intensity difference, there are peaks that are specific for each compound, i.e. energy losses at 2.5 and 28.5 eV in Co3O4 and at 36.1 eV in CoO. Consequently, ELS can be used to differentiate the two cobalt oxides and information complementary to XPS data can be obtained from the ELS data. (C) 2004 Elsevier B.V. All rights reserved.