Atomic resolution imaging of ultra-thin oxide films

项目概述：我们正在研究一种新型的混合材料，这种材料非常薄，既是表面又是界面。这些是生长在金衬底上的氧化物薄膜，只有一个原子层厚，可以在扫描隧道显微镜（STM）中以原子分辨率成像。薄膜的结构是薄膜系统所特有的，不是本体终止，并且通过与衬底的相互作用来确定。迄今为止，我们已经探索了Au（111）晶体衬底上的TiOx、NbOx、VOx和FeOx薄膜。这些系统对于理解贵金属催化剂的高温包封的影响具有根本重要性。这一过程被称为强金属载体相互作用，形成载体的材料（通常是钛酸盐）原子级薄膜迁移到催化剂颗粒上，阻止其发挥作用。该领域的新项目将集中在三元氧化物薄膜（如FeCrOx和其他混合金属氧化物薄膜）上。我们旨在回答两个问题。第一个涉及混合金属膜的稳定性，其中存在许多可能性，包括不同金属的相分离和金属的有序混合。这些信息对我们的理论合作者也很有价值，他们可以检查他们的模型，并从理论上探索大量的混合金属选项。第二个目的是了解点和扩展的缺陷，发生在薄膜以及调查的性能和原子结构的优先分子吸附位置。我们的研究方法将主要使用STM，但我们也打算将其与其他表面科学技术相结合，如低能电子衍射（LEED）和X射线光电子能谱（XPS）。根据光束线应用的结果，我们还打算在金刚石光源的I07和I05光束线处使用表面X射线衍射和角分辨光电子能谱来研究我们的薄膜。我们打算使用的另一种技术是执行STM图像帧平均，这使得能够增加与被平均的图像数量的根相关的图像的信噪比。在过去，我们已经实现了亚皮米的高度分辨率使用这种方法，它将有利于区分不同的阳离子在混合金属薄膜。

Project summary:We are working on a new class of hybrid material that is so thin it is both a surface and an interface. These are oxide films that are grown on gold substrates and are one atomic layer thick and can be imaged in the scanning tunnelling microscope (STM) with atomic resolution. The structure of the films is unique to the thin film system, is not a bulk termination, and is determined through the interaction with the substrate. To date we have explored TiOx, NbOx, VOx, and FeOx films on Au(111) crystal substrates. These systems are of fundamental importance to understanding the effects of high temperature encapsulation of noble metal catalysts. This is the process known as the strong metal support interaction, where an atomically thin film of the material forming the support, often a titanate, migrates over the catalyst particle and prevents it from functioning.The new project in this area will concentrate on ternary oxide films such as FeCrOx and other mixed-metal oxide films. We aim to answer two questions. The first relates the stability of the mixed metal films, where there are a number of possibilities including phase separation of the different metals, and ordered intermixing of the metals. This information is also of value to our theoretical collaborators who can check their models and explore a vast number of mixed-metal options theoretically. The second aim is to learn about point and extended defects that occur in the films as well as investigating the properties and atomic structure of preferential molecular adsorption locations. These studies are being carried out in order to identify potentially catalytically active sites.Our research methodology will be mainly to use STM, but we also intend to combine this with other surface science techniques such as low energy electron diffraction (LEED), and X-ray photoelectron spectroscopy (XPS). Depending on the outcome of beamline applications, we also intend to investigate our films using surface X-ray diffraction and angle resolved photoemission spectroscopy at the I07 and I05 beamlines at the Diamond Light Source. A further technique that we intend to use is to carry out STM image frame averaging, which enables an increase in the signal to noise ratio of the images that is related to the root of the number of images being averaged. In the past we have achieved sub-picometre height resolution using this method, and it will be advantageous in distinguishing the different cations in the mixed-metal films.This project falls within the EPSRC Surface Science research area.