Atomic resolution imaging of ultra-thin oxide films

项目总结：我们正在研究一种新型的混合材料，这种材料非常薄，它既是表面又是界面。这些是生长在金衬底上的氧化膜，厚度为一个原子层，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，不是一个体终止，而是通过与衬底的相互作用来确定的。迄今为止，我们已经在Au（111）晶体衬底上探索了TiOx、NbOx、VOx和FeOx薄膜。这些体系对于了解贵金属催化剂的高温包封效应具有重要意义。这是一个被称为强金属支撑相互作用的过程，在这个过程中，形成支撑的材料的原子薄膜，通常是钛酸盐，迁移到催化剂颗粒上，阻止它发挥作用。该领域的新项目将集中于三元氧化膜，如FeCrOx和其他混合金属氧化膜。我们打算回答两个问题。第一个与混合金属薄膜的稳定性有关，其中有许多可能性，包括不同金属的相分离，以及金属的有序混合。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，并在理论上探索大量的混合金属选项。第二个目的是了解发生在薄膜中的点缺陷和扩展缺陷，以及研究优先分子吸附位置的性质和原子结构。进行这些研究是为了确定潜在的催化活性位点。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光束线上使用表面x射线衍射和角度分辨光发射光谱来研究我们的薄膜。我们打算使用的另一种技术是进行STM图像帧平均，它可以增加图像的信噪比，这与被平均的图像数量的根有关。在过去，我们已经利用这种方法实现了亚皮米的高度分辨率，这将有利于区分混合金属薄膜中的不同阳离子。该项目属于EPSRC表面科学研究领域。

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.