金表面氧化和原子团簇的电子能谱研究

发布时间：2018-08-18 13:42

【摘要】：自纳米材料被发现以来,人们对它的探索就从未停歇,一直以来都是材料科学研究的热点。纳米材料表现出各种异于块体材料的新奇而迷人的特性,其在应用方面的巨大潜力令世人瞩目。探究其反常特性背后的物理机制是非常重要并极具价值的。然而将经典的理论模型直接应用于纳米材料均遇到了不同程度的阻碍,因此需要建立一个能够合理解释和预测纳米材料特性的全新的理论模型。我们以低配位原子作为切入点,在键弛豫理论的框架内对纳米材料进行探讨。低配位原子普遍的存在于任何材料中,但是在块体材料中低配原子所占比例极小,其对材料性能的影响微乎其微。而纳米材料中低配位原子占了很大的比例,其对材料的性能有着极大的影响。本文根据键弛豫理论和紧束缚近似,并结合X射线光电子能谱和选区标定光电子谱,对金表面、氧化和原子团簇的局部键弛豫和能级偏移进行分析,探讨其能级偏移的尺寸效应。具体工作和结果如下:1.键弛豫理论认为,低配位原子间的键将会变短变强,导致了电子和能量局域致密化,这将对晶体势产生微扰,使得表面的芯能级发生偏移。我们能够从理论上得到芯能级偏移与尺寸的对应关系。根据这个关系,可以对Au表面4f7/2芯能级的XPS进行解谱,得到孤立原子的结合能和块体能级的偏移等重要的定量信息,并对相关的物理量进行了预测。2.利用ZPS方法对Au表面发生氧化时4f7/2芯能级的偏移进行分析,结果显示强氧化性O原子的引入扰乱了表面的晶体结构和局部势场,引起表面形态的重构和芯能级的偏移。而表面重构对芯能级偏移亦有影响。3.对Au原子团簇芯带和价带进行ZPS分析,得到其各能级相对于块体材料的偏移量。原子团簇的能级均发生向深层的偏移,证实了BOLS理论的观点。此外,我们还发现芯带各能级的偏移量相同,而价带各能级偏移量大于芯带能级,并且价带顶端的能级要比底部的偏移量大。这意味着Au原子团簇的价带相比于块体材料来说变窄了,从而降低了价带电子发生跃迁所需的能量。此外,还得到芯能级尺寸效应的关系式,与实验数据有很好的一致性。理论分析与实验结果的一致性表明键弛豫理论-紧束缚近似方法在解释和预测低配位系统的能级偏移等方面是合理有效的,它能够为我们的科学研究和实际应用提供指导。
[Abstract]:Since the discovery of nanomaterials, it has been a hot topic in material science. Nanomaterials exhibit novel and attractive properties different from bulk materials, and their potential applications have attracted worldwide attention. It is very important and valuable to explore the physical mechanism behind its anomalous properties. However, the direct application of classical theoretical models to nanomaterials has encountered various obstacles, so it is necessary to establish a new theoretical model that can reasonably explain and predict the properties of nanomaterials. In the framework of bond relaxation theory, the nanocrystalline materials are investigated by using low coordination atoms as the starting point. Low coordination atoms generally exist in any material, but the proportion of low ligand atoms in bulk materials is very small, which has little effect on the properties of materials. However, low coordination atoms account for a large proportion of nanomaterials, which have a great impact on the properties of the materials. Based on bond relaxation theory and tight-binding approximation, combined with X-ray photoelectron spectroscopy and selective calibration photoelectron spectroscopy, the local bond relaxation and energy level migration of gold surface, oxidation and atomic clusters are analyzed. The size effect of energy level shift is discussed. The specific work and results are as follows: 1. The bond relaxation theory holds that the bond between the low coordination atoms will become shorter and stronger, resulting in the localized densification of electrons and energy, which will cause perturbation to the crystal potential and make the core energy levels on the surface offset. We can theoretically get the corresponding relation between the core energy level shift and the size. According to this relation, the XPS spectra of 4f7/2 core energy levels on au surface can be obtained, and some important quantitative information, such as the binding energy of isolated atoms and the shift of block physical level, can be obtained, and the related physical quantities are predicted. The ZPS method is used to analyze the migration of the 4f7/2 core energy level during the oxidation of au surface. The results show that the introduction of strongly oxidized O atoms disturbs the crystal structure and local potential field of the surface, resulting in the reconstruction of the surface morphology and the migration of the core energy level. The surface reconstruction also has an effect on the core energy level shift. The ZPS analysis of au cluster core band and valence band is carried out, and the migration of each energy level relative to the bulk material is obtained. The energy levels of the cluster are all shifted to the deep layer, which confirms the viewpoint of BOLS theory. In addition, we also find that the migration of each energy level in the core band is the same, while the shift of the valence band level is larger than that of the core band level, and the energy level at the top of the valence band is larger than that at the bottom. This means that the valence band of au clusters is narrower than that of bulk materials, thus reducing the energy required for the transition of valence band electrons. In addition, the relation of the size effect of the core energy level is obtained, which is in good agreement with the experimental data. The agreement between the theoretical analysis and the experimental results shows that the bond relaxation theory-tight-binding approximation method is reasonable and effective in explaining and predicting the energy level shift of low coordination system. It can provide guidance for our scientific research and practical application.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O614.123;TB383.1

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