Atomic resolution imaging of ultra-thin oxide films

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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.