Atomic-scale imaging on metal oxide surfaces with a chemically selective scanning probe tip

Basic data for this project

Description

The atomic structure of metal oxide surfaces largely determines their properties, which are important for a variety of applications ranging from energy conversion and oxide electronics, to data storage, heterogeneous catalysis and biomedical sciences. While scanning probe microscopy (SPM) techniques are powerful in accessing the local atomic structure, elemental discrimination in SPM data is a major challenge. Especially due to the often-unknown chemical identity of the probe-tip terminating atom, which decisively determines the SPM contrast. As a consequence, elemental recognition on the atomic-scale usually relies on indirect structural considerations, which are prone to errors and require extensive theoretical modelling. In the past decade, tip functionalization with single CO molecules at the apex have advanced to a standard tool for noncontact atomic force microscopy (NC-AFM) for studies on organic nano-materials allowing for a drastically increased resolution. In our previous work, we established oxygen-terminated Cu-tips (CuOx-tips), as an attractive alternative, which due to their higher rigidity allow reducing imaging artefacts. Recently, we furthermore demonstrated a remarkable chemical selectivity of CuOx-tips in NC-AFM experiments on metal oxide surfaces. The present project sets out to systematically investigate if this finding can be generalized to the class of metal oxide materials. To achieve this goal, a variety of different surfaces of the most important metal oxide systems will be investigated by CuOx-tip NC-AFM imaging and force spectroscopy. The experiments will be performed on surfaces with an increasing complexity and disorder to critically explore the potential of this methodology. They will be complemented by ab-initio modelling to relate structural models and related defects with the charge distributions and site selective force interaction. To benchmark theoretical modelling, we will initially focus on oxygen-induced surface reconstructions on different metal substrates, which show both, largely well-known structures, but also highly complex reconstructions with a high degree of disorder. The next steps of the project will focus on the binary bulk metal oxides hematite, magnetite, and titanium dioxide. Finally, we will turn to different facets of the ternary perovskites SrTiO3 and KTaO3, which will serve as ultimate test cases. In general, we will usually start with the prototypical surfaces of the various materials serving as benchmarks before we increase the complexity step-by-step toward the more complex and unknown facets and reconstructions. Establishing CuOx-tips as standardized probe tips for chemical imaging on the investigated highly relevant surface terminations will allow to reach a completely new level in metal-oxide surface- and defect characterization.